## Summary

This document describes the geometry of regions available for spatial filtering in IRAF/PROS analysis.

## Geometric shapes

Several geometric shapes are used to describe regions. The valid shapes are:

```  shape:        arguments:
-----         ----------------------------------------
BOX           xcenter ycenter xwidth yheight (angle)
ELLIPSE       xcenter ycenter xwidth yheight (angle)
FIELD         none
LINE          x1 y1 x2 y2
PIE           xcenter ycenter angle1 angle2
POINT         x1 y1
POLYGON       x1 y1 x2 y2 ... xn yn
```
All arguments are real values; integer values are automatically converted to real where necessary. All angles are in degrees and specify angles that run counter-clockwise from the positive y-axis.

Shapes can be specified using "command" syntax:

```  [shape] arg1 arg2 ...
```
or using "routine" syntax:
```  [shape](arg1, arg2, ...)
```
or by any combination of the these. (Of course, the parentheses must balance and there cannot be more commas than necessary.) The shape keywords are case-insensitive. Furthermore, any shape can be specified by a three-character unique abbreviation. For example, one can specify three circular regions as:
```  "foo.fits[CIRCLE 512 512 50;CIR(128 128, 10);cir(650,650,20)]"
```
(Quotes generally are required to protect the region descriptor from being processed by the Unix shell.)

The annulus shape specifies annuli, centered at xcenter, ycenter, with inner and outer radii (r1, r2). For example,

```  ANNULUS 25 25 5 10
```
specifies an annulus centered at 25.0 25.0 with an inner radius of 5.0 and an outer radius of 10. Assuming (as will be done for all examples in this document, unless otherwise noted) this shape is used in a mask of size 40x40, it will look like this:
```	1234567890123456789012345678901234567890
----------------------------------------
40:........................................
39:........................................
38:........................................
37:........................................
36:........................................
35:........................................
34:....................111111111...........
33:...................11111111111..........
32:.................111111111111111........
31:.................111111111111111........
30:................11111111111111111.......
29:...............1111111.....1111111......
28:...............111111.......111111......
27:...............11111.........11111......
26:...............11111.........11111......
25:...............11111.........11111......
24:...............11111.........11111......
23:...............11111.........11111......
22:...............111111.......111111......
21:...............1111111.....1111111......
20:................11111111111111111.......
19:.................111111111111111........
18:.................111111111111111........
17:...................11111111111..........
16:....................111111111...........
15:........................................
14:........................................
13:........................................
12:........................................
11:........................................
10:........................................
9:........................................
8:........................................
7:........................................
6:........................................
5:........................................
4:........................................
3:........................................
2:........................................
1:........................................
```

The box shape specifies an orthogonally oriented box, centered at xcenter, ycenter, of size xwidth, yheight. It requires four arguments and accepts an optional fifth argument to specify a rotation angle. When the rotation angle is specified (in degrees), the box is rotated by an angle that runs counter-clockwise from the positive y-axis.

The box shape specifies a rotated box, centered at xcenter, ycenter, of size xwidth, yheight. The box is rotated by an angle specified in degrees that runs counter-clockwise from the positive y-axis. If the angle argument is omitted, it defaults to 0.

The circle shape specifies a circle, centered at xcenter, ycenter, of radius r. It requires three arguments.

The ellipse shape specifies an ellipse, centered at xcenter, ycenter, with y-axis width a and the y-axis length b defined such that:

```  x**2/a**2 + y**2/b**2 = 1
```
Note that a can be less than, equal to, or greater than b. The ellipse is rotated the specified number of degrees. The rotation is done according to astronomical convention, counter-clockwise from the positive y-axis. An ellipse defined by:
```  ELLIPSE 20 20 5 10 45
```
will look like this:
```         1234567890123456789012345678901234567890
----------------------------------------
40:........................................
39:........................................
38:........................................
37:........................................
36:........................................
35:........................................
34:........................................
33:........................................
32:........................................
31:........................................
30:........................................
29:........................................
28:........................................
27:............111111......................
26:............11111111....................
25:............111111111...................
24:............11111111111.................
23:............111111111111................
22:............111111111111................
21:.............111111111111...............
20:.............1111111111111..............
19:..............111111111111..............
18:...............111111111111.............
17:...............111111111111.............
16:................11111111111.............
15:..................111111111.............
14:...................11111111.............
13:.....................111111.............
12:........................................
11:........................................
10:........................................
9:........................................
8:........................................
7:........................................
6:........................................
5:........................................
4:........................................
3:........................................
2:........................................
1:........................................
```

The field shape specifies the entire field as a region. It is not usually specified explicitly, but is used implicitly in the case where no regions are specified, that is, in cases where either a null string or some abbreviation of the string "none" is input. Field takes no arguments.

The pie shape specifies an angular wedge of the entire field, centered at xcenter, ycenter. The wedge runs between the two specified angles. The angles are given in degrees, running counter-clockwise from the positive x-axis. For example,

```  PIE 20 20 90 180
```
defines a region from 90 degrees to 180 degrees, i.e., quadrant 2 of the Cartesian plane. The display of such a region looks like this:
```	1234567890123456789012345678901234567890
----------------------------------------
40:11111111111111111111....................
39:11111111111111111111....................
38:11111111111111111111....................
37:11111111111111111111....................
36:11111111111111111111....................
35:11111111111111111111....................
34:11111111111111111111....................
33:11111111111111111111....................
32:11111111111111111111....................
31:11111111111111111111....................
30:11111111111111111111....................
29:11111111111111111111....................
28:11111111111111111111....................
27:11111111111111111111....................
26:11111111111111111111....................
25:11111111111111111111....................
24:11111111111111111111....................
23:11111111111111111111....................
22:11111111111111111111....................
21:11111111111111111111....................
20:........................................
19:........................................
18:........................................
17:........................................
16:........................................
15:........................................
14:........................................
13:........................................
12:........................................
11:........................................
10:........................................
9:........................................
8:........................................
7:........................................
6:........................................
5:........................................
4:........................................
3:........................................
2:........................................
1:........................................
```
The pie slice specified is always a counter-clockwise sweep between the angles, starting at the first angle and ending at the second. Thus:
```  PIE 10 15 30 60
```
describes a 30 degree sweep from 2 o'clock to 1 o'clock, while:
```  PIE 10 15 60 30
```
describes a 330 degree counter-clockwise sweep from 1 o'clock to 2 o'clock passing through 12 o'clock (0 degrees). Note in both of these examples that the center of the slice can be anywhere on the plane. The second mask looks like this:
```	1234567890123456789012345678901234567890
----------------------------------------
40:111111111111111111111111................
39:11111111111111111111111.................
38:11111111111111111111111.................
37:1111111111111111111111..................
36:1111111111111111111111..................
35:111111111111111111111...................
34:11111111111111111111....................
33:11111111111111111111....................
32:1111111111111111111....................1
31:1111111111111111111..................111
30:111111111111111111.................11111
29:111111111111111111................111111
28:11111111111111111...............11111111
27:1111111111111111..............1111111111
26:1111111111111111.............11111111111
25:111111111111111............1111111111111
24:111111111111111..........111111111111111
23:11111111111111.........11111111111111111
22:11111111111111........111111111111111111
21:1111111111111.......11111111111111111111
20:111111111111......1111111111111111111111
19:111111111111....111111111111111111111111
18:11111111111....1111111111111111111111111
17:11111111111..111111111111111111111111111
16:1111111111.11111111111111111111111111111
15:1111111111111111111111111111111111111111
14:1111111111111111111111111111111111111111
13:1111111111111111111111111111111111111111
12:1111111111111111111111111111111111111111
11:1111111111111111111111111111111111111111
10:1111111111111111111111111111111111111111
9:1111111111111111111111111111111111111111
8:1111111111111111111111111111111111111111
7:1111111111111111111111111111111111111111
6:1111111111111111111111111111111111111111
5:1111111111111111111111111111111111111111
4:1111111111111111111111111111111111111111
3:1111111111111111111111111111111111111111
2:1111111111111111111111111111111111111111
1:1111111111111111111111111111111111111111
```
The pie slice goes to the edge of the field. To limit its scope, pie usually is is combined with other shapes, such as circles and annuli, using boolean operations. (See below and in "help regalgebra").

Pie Performance Notes:

Pie region processing time is proportional to the size of the image, and not the size of the region. This is because the pie shape is the only infinite length shape, and we essentially must check all y rows for inclusion (unlike other regions, where the y limits can be calculated beforehand). Thus, pie can run very slowly on large images. In particular, it will run MUCH more slowly than the panda shape in image-based region operations (such as funcnts). We recommend use of panda over pie where ever possible.

If you must use pie, always try to put it last in a boolean && expression. The reason for this is that the filter code is optimized to exit as soon as the result is know. Since pie is the slowest region, it is better to avoid executing it if another region can decide the result. Consider, for example, the difference in time required to process a Chandra ACIS file when a pie and circle are combined in two different orders:

```  time ./funcnts nacis.fits "circle 4096 4096 100 && pie 4096 4096 10 78"
2.87u 0.38s 0:35.08 9.2%

time ./funcnts nacis.fits "pie 4096 4096 10 78 && circle 4096 4096 100 "
89.73u 0.36s 1:03.50 141.8%
```

Black-magic performance note:

Panda region processing uses a quick test pie region instead of the normal pie region when combining its annulus and pie shapes. This qtpie shape differs from the normal pie in that it utilizes the y limits from the previous region with which it is combined. In a panda shape, which is a series of annuli combined with pies, the processing time is thus reduced to that of the annuli.

You can use the qtpie shape instead of pie in cases where you are combining pie with another shape using the && operator. This will cause the pie limits to be set using limits from the other shape, and will speed up the processing considerably. For example, the above execution of funcnts can be improved considerably using this technique:

```  time ./funcnts nacis.fits "circle 4096 4096 100 && qtpie 4096 4096 10 78"
4.66u 0.33s 0:05.87 85.0%
```

We emphasize that this is a quasi-documented feature and might change in the future. The qtpie shape is not recognized by ds9 or other programs.

The line shape allows single pixels in a line between (x1,y1) and (x2,y2) to be included or excluded. For example:

```  LINE (5,6, 24,25)
displays as:
1234567890123456789012345678901234567890
----------------------------------------
40:........................................
39:........................................
38:........................................
37:........................................
36:........................................
35:........................................
34:........................................
33:........................................
32:........................................
31:........................................
30:........................................
29:........................................
28:........................................
27:........................................
26:........................................
25:.......................1................
24:......................1.................
23:.....................1..................
22:....................1...................
21:...................1....................
20:..................1.....................
19:.................1......................
18:................1.......................
17:...............1........................
16:..............1.........................
15:.............1..........................
14:............1...........................
13:...........1............................
12:..........1.............................
11:.........1..............................
10:........1...............................
9:.......1................................
8:......1.................................
7:.....1..................................
6:....1...................................
5:........................................
4:........................................
3:........................................
2:........................................
1:........................................

The point shape allows single pixels to be included or
excluded.  Although the (x,y) values are real numbers, they are truncated
to integer and the corresponding pixel is included or excluded, as specified.

Several points can be put in one region declaration; unlike the
original IRAF implementation, each now is given a different region mask value.
This makes it easier, for example, for funcnts to determine the number of
photons in the individual pixels. For example,
POINT (5,6,  10,11,  20,20,  35,30)

will give the different region mask values to all four points, as shown below:

1234567890123456789012345678901234567890
----------------------------------------
40:........................................
39:........................................
38:........................................
37:........................................
36:........................................
35:........................................
34:........................................
33:........................................
32:........................................
31:........................................
30:..................................4.....
29:........................................
28:........................................
27:........................................
26:........................................
25:........................................
24:........................................
23:........................................
22:........................................
21:........................................
20:...................3....................
19:........................................
18:........................................
17:........................................
16:........................................
15:........................................
14:........................................
13:........................................
12:........................................
11:.........2..............................
10:........................................
9:........................................
8:........................................
7:........................................
6:....1...................................
5:........................................
4:........................................
3:........................................
2:........................................
1:........................................

The polygon shape specifies a polygon with vertices
(x1, y1) ... (xn, yn). The polygon is closed automatically: one should
not specify the last vertex to be the same as the first.  Any number of
vertices are allowed.  For example, the following polygon defines a
right triangle as shown below:
POLYGON (10,10,  10,30,  30,30)

looks like this:

1234567890123456789012345678901234567890
----------------------------------------
40:........................................
39:........................................
38:........................................
37:........................................
36:........................................
35:........................................
34:........................................
33:........................................
32:........................................
31:........................................
30:..........11111111111111111111..........
29:..........1111111111111111111...........
28:..........111111111111111111............
27:..........11111111111111111.............
26:..........1111111111111111..............
25:..........111111111111111...............
24:..........11111111111111................
23:..........1111111111111.................
22:..........111111111111..................
21:..........11111111111...................
20:..........1111111111....................
19:..........111111111.....................
18:..........11111111......................
17:..........1111111.......................
16:..........111111........................
15:..........11111.........................
14:..........1111..........................
13:..........111...........................
12:..........11............................
11:..........1.............................
10:........................................
9:........................................
8:........................................
7:........................................
6:........................................
5:........................................
4:........................................
3:........................................
2:........................................
1:........................................

Note that polygons can get twisted upon themselves if edge lines
cross.  Thus:
POL (10,10,  20,20,  20,10,  10,20)

will produce an area which is two triangles, like butterfly wings, as shown
below:

1234567890123456789012345678901234567890
----------------------------------------
40:........................................
39:........................................
38:........................................
37:........................................
36:........................................
35:........................................
34:........................................
33:........................................
32:........................................
31:........................................
30:........................................
29:........................................
28:........................................
27:........................................
26:........................................
25:........................................
24:........................................
23:........................................
22:........................................
21:........................................
20:........................................
19:..........1........1....................
18:..........11......11....................
17:..........111....111....................
16:..........1111..1111....................
15:..........1111111111....................
14:..........1111..1111....................
13:..........111....111....................
12:..........11......11....................
11:..........1........1....................
10:........................................
9:........................................
8:........................................
7:........................................
6:........................................
5:........................................
4:........................................
3:........................................
2:........................................
1:........................................

The following are combinations of pie with different shapes
(called "panda" for "Pie AND Annulus") allow for easy specification of
shape:   arguments:
-----    ---------
BPANDA   xcen ycen ang1 ang2 nang xwlo yhlo xwhi yhhi nrad (ang) # box
EPANDA   xcen ycen ang1 ang2 nang xwlo yhlo xwhi yhhi nrad (ang) # ellipse

The panda (Pies AND Annuli) shape can be
used to create combinations of pie and annuli markers. It is analogous
to a Cartesian product on those shapes, i.e., the result is several
shapes generated by performing a boolean AND between pies and
annuli. Thus, the panda and cpanda specify combinations of annulus and
circle with pie, respectively and give identical results. The bpanda
combines box and pie, while epanda combines ellipse and pie.

Consider the example shown below:
PANDA(20,20, 0,360,3, 0,15,4)

Here, 3 pie slices centered at 20, 20 are combined with 4 annuli, also
centered at 20, 20. The result is a mask with 12 regions (displayed in
base 16 to save characters):
1234567890123456789012345678901234567890
----------------------------------------
40:........................................
39:........................................
38:........................................
37:........................................
36:........................................
35:........................................
34:..............44444444444...............
33:............444444444444444.............
32:...........88444444444444444............
31:.........888844443333344444444..........
30:........88888833333333333444444.........
29:........88888733333333333344444.........
28:.......8888877733333333333344444........
27:......888887777332222233333344444.......
26:......888877777622222222333334444.......
25:.....88887777766622222222333334444......
24:.....88887777666622222222233334444......
23:.....88887777666651111222233334444......
22:.....88877776666551111122223333444......
21:.....88877776666555111122223333444......
20:.....888777766665559999aaaabbbbccc......
19:.....888777766665559999aaaabbbbccc......
18:.....888777766665599999aaaabbbbccc......
17:.....88887777666659999aaaabbbbcccc......
16:.....888877776666aaaaaaaaabbbbcccc......
15:.....888877777666aaaaaaaabbbbbcccc......
14:......8888777776aaaaaaaabbbbbcccc.......
13:......888887777bbaaaaabbbbbbccccc.......
12:.......88888777bbbbbbbbbbbbccccc........
11:........888887bbbbbbbbbbbbccccc.........
10:........888888bbbbbbbbbbbcccccc.........
9:.........8888ccccbbbbbcccccccc..........
8:...........88ccccccccccccccc............
7:............ccccccccccccccc.............
6:..............ccccccccccc...............
5:........................................
4:........................................
3:........................................
2:........................................
1:........................................

Several regions with different mask values can be combined in the
same mask.  This supports comparing data from the different regions.
(For information on how to combine different shapes into a single
region, see "help regalgebra".)  For example, consider the following
set of regions:
ANNULUS 25 25 5 10
ELLIPSE 20 20 5 10 315
BOX 15 15 5 10

The resulting mask will look as follows:

1234567890123456789012345678901234567890
----------------------------------------
40:........................................
39:........................................
38:........................................
37:........................................
36:........................................
35:........................................
34:....................111111111...........
33:...................11111111111..........
32:.................111111111111111........
31:.................111111111111111........
30:................11111111111111111.......
29:...............1111111.....1111111......
28:...............111111.......111111......
27:...............11111.222222..11111......
26:...............111112222222..11111......
25:...............111112222222..11111......
24:...............111112222222..11111......
23:...............111112222222..11111......
22:...............111111222222.111111......
21:..............211111112222.1111111......
20:............322211111111111111111.......
19:............32222111111111111111........
18:............22222111111111111111........
17:............222222211111111111..........
16:............22222222111111111...........
15:............222222222...................
14:............22222222....................
13:............222222......................
12:............33333.......................
11:............33333.......................
10:........................................
9:........................................
8:........................................
7:........................................
6:........................................
5:........................................
4:........................................
3:........................................
2:........................................
1:........................................

Note that when a pixel is in 2 or more regions, it is arbitrarily
assigned to a one of the regions in question (often based on how a
give C compiler optimizes boolean expressions).

Region accelerators

Two types of \fBaccelerators, to simplify region specification,
are provided as natural extensions to the ways shapes are described.
These are: extended lists of parameters, specifying multiple regions,
valid for annulus, box, circle, ellipse, pie, and points; and
n=, valid for annulus, box, circle, ellipse, and pie (not
point).  In both cases, one specification is used to define several
different regions, that is, to define shapes with different mask

The following regions accept accelerator syntax:
shape      arguments
-----      ------------------------------------------
BOX        xcenter ycenter xw1 yh1 xw2 yh2 ... xwn yhn (angle)
BOX        xcenter ycenter xwlo yhlo xwhi yhhi n=[number] (angle)
CIRCLE     xcenter ycenter r1 r2 ... rn              # same as annulus
CIRCLE     xcenter ycenter rinner router n=[number]  # same as annulus
ELLIPSE    xcenter ycenter xw1 yh1 xw2 yh2 ... xwn yhn (angle)
ELLIPSE    xcenter ycenter xwlo yhlo xwhi yhhi n=[number] (angle)
PIE        xcenter ycenter angle1 angle2 (angle3) (angle4) (angle5) ...
PIE        xcenter ycenter angle1 angle2 (n=[number])
POINT      x1 y1 x2 y2 ... xn yn

Note that the circle accelerators are simply aliases for the annulus
accelerators.

For example, several annuli at the same center can be specified in one
region expression by specifying more than two radii.  If N
radii are specified, then N-1 annuli result, with the outer
succeeding annulus.  Each annulus is considered a separate region, and
is given a separate mask value. For example,
ANNULUS 20 20 0 2 5 10 15 20

specifies five different annuli centered at 20 20, and is equivalent to:
ANNULUS 20.0 20.0  0  2
ANNULUS 20.0 20.0  2  5
ANNULUS 20.0 20.0  5 10
ANNULUS 20.0 20.0 10 15
ANNULUS 20.0 20.0 15 20

1234567890123456789012345678901234567890
----------------------------------------
40:........................................
39:.............5555555555555..............
38:...........55555555555555555............
37:.........555555555555555555555..........
36:........55555555555555555555555.........
35:......555555555555555555555555555.......
34:.....55555555544444444444555555555......
33:....5555555544444444444444455555555.....
32:....5555555444444444444444445555555.....
31:...555555444444444444444444444555555....
30:..55555544444444444444444444444555555...
29:..55555544444443333333334444444555555...
28:.5555554444444333333333334444444555555..
27:.5555544444433333333333333344444455555..
26:555555444444333333333333333444444555555.
25:555554444443333333333333333344444455555.
24:555554444433333332222233333334444455555.
23:555554444433333322222223333334444455555.
22:555554444433333222222222333334444455555.
21:555554444433333222111222333334444455555.
20:555554444433333222111222333334444455555.
19:555554444433333222111222333334444455555.
18:555554444433333222222222333334444455555.
17:555554444433333322222223333334444455555.
16:555554444433333332222233333334444455555.
15:555554444443333333333333333344444455555.
14:555555444444333333333333333444444555555.
13:.5555544444433333333333333344444455555..
12:.5555554444444333333333334444444555555..
11:..55555544444443333333334444444555555...
10:..55555544444444444444444444444555555...
9:...555555444444444444444444444555555....
8:....5555555444444444444444445555555.....
7:....5555555544444444444444455555555.....
6:.....55555555544444444444555555555......
5:......555555555555555555555555555.......
4:........55555555555555555555555.........
3:.........555555555555555555555..........
2:...........55555555555555555............
1:.............5555555555555..............

For boxes and ellipses, if an odd number of arguments is specified,
then the last argument is assumed to be an angle. Otherwise, the
angle is assumed to be zero. For example:
ellipse 20 20 3 5 6 10 9 15 12 20 45

specifies an 3 ellipses at a 45 degree angle:
1234567890123456789012345678901234567890
----------------------------------------
40:........................................
39:........................................
38:........................................
37:........................................
36:........33333333........................
35:......333333333333......................
34:.....3333333333333333...................
33:....333333333333333333..................
32:....33333332222233333333................
31:...3333332222222222333333...............
30:...33333222222222222233333..............
29:...333332222222222222223333.............
28:...3333222222211112222223333............
27:...33332222211111111222223333...........
26:...333322222111111111122223333..........
25:...3333222211111111111122223333.........
24:....3332222111111..1111122223333........
23:....333322211111.....11112222333........
22:....33332222111.......11112223333.......
21:.....33322221111.......11122223333......
20:.....33332221111.......11112223333......
19:.....33332222111.......11112222333......
18:......33332221111.......11122223333.....
17:.......33322221111.....111112223333.....
16:.......3333222211111..1111112222333.....
15:........3333222211111111111122223333....
14:.........333322221111111111222223333....
13:..........33332222211111111222223333....
12:...........3333222222111122222223333....
11:............333322222222222222233333....
10:.............33333222222222222233333....
9:..............3333332222222222333333....
8:...............33333333222223333333.....
7:.................333333333333333333.....
6:..................3333333333333333......
5:.....................333333333333.......
4:.......................33333333.........
3:........................................
2:........................................
1:........................................

Note in the above example that the lower limit is not part of the
region for boxes, circles, and ellipses. This makes circles and annuli
equivalent, i.e.:
circle  20 20 5 10 15 20
annulus 20 20 5 10 15 20

both give the following region mask:
1234567890123456789012345678901234567890
----------------------------------------
40:........................................
39:.............3333333333333..............
38:...........33333333333333333............
37:.........333333333333333333333..........
36:........33333333333333333333333.........
35:......333333333333333333333333333.......
34:.....33333333322222222222333333333......
33:....3333333322222222222222233333333.....
32:....3333333222222222222222223333333.....
31:...333333222222222222222222222333333....
30:..33333322222222222222222222222333333...
29:..33333322222221111111112222222333333...
28:.3333332222222111111111112222222333333..
27:.3333322222211111111111111122222233333..
26:333333222222111111111111111222222333333.
25:333332222221111111111111111122222233333.
24:33333222221111111.....11111112222233333.
23:3333322222111111.......1111112222233333.
22:333332222211111.........111112222233333.
21:333332222211111.........111112222233333.
20:333332222211111.........111112222233333.
19:333332222211111.........111112222233333.
18:333332222211111.........111112222233333.
17:3333322222111111.......1111112222233333.
16:33333222221111111.....11111112222233333.
15:333332222221111111111111111122222233333.
14:333333222222111111111111111222222333333.
13:.3333322222211111111111111122222233333..
12:.3333332222222111111111112222222333333..
11:..33333322222221111111112222222333333...
10:..33333322222222222222222222222333333...
9:...333333222222222222222222222333333....
8:....3333333222222222222222223333333.....
7:....3333333322222222222222233333333.....
6:.....33333333322222222222333333333......
5:......333333333333333333333333333.......
4:........33333333333333333333333.........
3:.........333333333333333333333..........
2:...........33333333333333333............
1:.............3333333333333..............

As a final example, specifying several angles in one pie slice
expression is equivalent to specifying several separate slices with
the same center.  As with the annulus, if N angles are
specified, then N-1 slices result, with the ending angle of
each preceding slice being the starting angle of the succeeding slice.
Each slice is considered a separate region, and is given a separate
PIE 12 12 315 45 115 270

specifies three regions as shown below:
1234567890123456789012345678901234567890
----------------------------------------
40:2222222222222222222222222222222222222222
39:2222222222222222222222222222222222222221
38:2222222222222222222222222222222222222211
37:2222222222222222222222222222222222222111
36:2222222222222222222222222222222222221111
35:3222222222222222222222222222222222211111
34:3222222222222222222222222222222222111111
33:3322222222222222222222222222222221111111
32:3322222222222222222222222222222211111111
31:3332222222222222222222222222222111111111
30:3332222222222222222222222222221111111111
29:3333222222222222222222222222211111111111
28:3333222222222222222222222222111111111111
27:3333322222222222222222222221111111111111
26:3333322222222222222222222211111111111111
25:3333322222222222222222222111111111111111
24:3333332222222222222222221111111111111111
23:3333332222222222222222211111111111111111
22:3333333222222222222222111111111111111111
21:3333333222222222222221111111111111111111
20:3333333322222222222211111111111111111111
19:3333333322222222222111111111111111111111
18:3333333332222222221111111111111111111111
17:3333333332222222211111111111111111111111
16:3333333333222222111111111111111111111111
15:3333333333222221111111111111111111111111
14:3333333333322211111111111111111111111111
13:3333333333322111111111111111111111111111
12:33333333333.1111111111111111111111111111
11:3333333333331111111111111111111111111111
10:333333333333.111111111111111111111111111
9:333333333333..11111111111111111111111111
8:333333333333...1111111111111111111111111
7:333333333333....111111111111111111111111
6:333333333333.....11111111111111111111111
5:333333333333......1111111111111111111111
4:333333333333.......111111111111111111111
3:333333333333........11111111111111111111
2:333333333333.........1111111111111111111
1:333333333333..........111111111111111111

The annulus, box, circle, ellipse, and pie shapes also accept an
n=[int] syntax for specifying multiple regions. The
n=[int]syntax interprets the previous (shape-dependent)
arguments as lower and upper limits for the region and creates n
shapes with evenly spaced boundaries.  For example, if n=[int]
is specified in an annulus, the two immediately preceding radii
(rn and rm) are divided into int annuli, such
that the inner radius of the first is rn and the outer radius
of the last is rm. For example,
ANNULUS 20 20 5 20 n=3

is equivalent to:
ANNULUS 20 20 5 10 15 20

If this syntax is used with an ellipse or box, then the two preceding
pairs of values are taken to be lower and upper limits for a set of
ellipses or boxes. A circle uses the two preceding arguments for upper
and lower radii.  For pie, the two preceding angles are divided into n
wedges such that the starting angle of the first is the lower bound
and the ending angle of the last is the upper bound.  In all cases,
the n=[int] syntax allows any single alphabetic character
before the "=", i.e, i=3, z=3, etc. are all equivalent.

Also note that for boxes and ellipses, the optional angle argument is
always specified after the n=[int] syntax. For example:
ellipse 20 20 4 6 16 24 n=3 45
specifies 3 elliptical regions at an angle of 45 degrees:

1234567890123456789012345678901234567890
----------------------------------------
40:........33333333........................
39:.....33333333333333.....................
38:....33333333333333333...................
37:...33333333333333333333.................
36:..33333333333333333333333...............
35:.3333333333222223333333333..............
34:3333333322222222222233333333............
33:33333332222222222222223333333...........
32:333333222222222222222222333333..........
31:3333322222222222222222222333333.........
30:33333222222222111122222222333333........
29:333332222222111111112222222333333.......
28:3333222222211111111111222222333333......
27:3333222222111111111111112222233333......
26:33332222221111111111111112222233333.....
25:33332222211111111.111111112222233333....
24:333322222111111......111111222223333....
23:333322222111111.......111112222233333...
22:33333222221111.........11111222223333...
21:333332222211111.........11112222233333..
20:.33332222211111.........11111222223333..
19:.33333222221111.........111112222233333.
18:..33332222211111.........11112222233333.
17:..333332222211111.......111111222233333.
16:...333322222111111......111111222223333.
15:...333332222211111111.111111112222233333
14:....333332222211111111111111122222233333
13:.....33333222221111111111111122222233333
12:.....33333322222211111111111222222233333
11:......3333332222222111111112222222333333
10:.......333333222222221111222222222333333
9:........33333322222222222222222222333333
8:.........333333222222222222222222333333.
7:..........33333332222222222222223333333.
6:...........3333333322222222222233333333.
5:.............3333333333222223333333333..
4:..............33333333333333333333333...
3:................33333333333333333333....
2:..................33333333333333333.....
1:....................33333333333333......

Both the variable argument syntax and the n=[int] syntax must
occur alone in a region descriptor (aside from the optional angle for
boxes and ellipses).  They cannot be combined. Thus, it is not valid
to precede or follow an n=[int] accelerator with more angles or
# INVALID -- one too many angles before a=5 ...
# and no angles are allowed after a=5
PIE 12 12 10 25 50 a=5 85 135

Instead, use three separate specifications, such as:
PIE 12 12 10 25
PIE 12 12 25 50 a=5
PIE 12 12 85 135

The original (IRAF) implementation of region filtering permitted this
looser syntax, but we found it caused more confusion than it was worth
and therefore removed it.

NB: Accelerators may be combined with other shapes in a boolean
expression in any order. (This is a change starting with funtools
v1.1.1. Prior to this release, the accelerator shape had to be
specified last).  The actual region mask id values returned depend on the
order in which the shapes are specified, although the total number of
pixels or rows that pass the filter will be consistent. For this
reason, use of accelerators in boolean expressions is discouraged in
programs such as funcnts, where region mask id values are used
to count events or image pixels.

[All region masks displayed in this document were generated using the
fundisp routine and the undocumented "mask=all" argument (with
spaced removed using sed ):
fundisp "funtools/funtest/test40.fits[ANNULUS 25 25 5 10]" mask=all |\
sed 's/ //g'

Note that you must supply an image of the appropriate size -- in this case,
a FITS image of dimension 40x40 is used.]

Go to Funtools Help Index

Last updated: March 12, 2007

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