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NRAO Home > CASA > CASA Toolkit Reference Manual |
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regionmanager.difference - Function
1.1.2 Create the difference of two world regions
Description
This function (short-hand name diff) creates a region which is the difference
of two world regions. The order of the regions is important.
The difference consists of all pixels masked-on in the first region and not masked-on in the second region.
Arguments
Inputs |
| ||
region1 |
| The first world region
| |
| allowed: | record | |
| Default: | ||
region2 |
| The second world region
| |
| allowed: | record |
|
| Default: | Region tool |
|
comment |
| A comment stored with the region
| |
| allowed: | string |
|
| Default: | String |
|
record
Example
- ia.open(’hcn’)
- csys = ia.coordsys()
- rg.setcoordinates(csys.torecord())
-
- blc = "10pix 10pix"
- trc = "60pix 60pix"
- r1 = rg.wbox(blc,trc,[0,1])
-
- blc = "50pix 50pix"
- trc = "80pix 80pix"
- r2 = rg.wbox(blc, trc, [0,1])
-
- r3 = rg.difference(r1, r2) # r1 - r2
-
- ia.statistics(region=r1) # Some output discarded
Selected bounding box [10, 10] to [60, 60]
No pts = 2601
-
- ia.statistics(region=r3) # Some output discarded
Selected bounding box [10, 10] to [60, 60]
No pts = 2480
-
-
- r4 = rg.difference(r2, r1) # r2 - r1
-
- ia.statistics(region=r2) # Some output discarded
Selected bounding box [50, 50] to [80, 80]
No pts = 961
-
- ia.statistics(region=r4) # Some output discarded
Selected bounding box [50, 50, 1] to [80, 80, 64]
No pts = 840
We use pixel units and boxes in this example to make it clear what is
happening. The two regions overlap in the top right corner area of
region {\stf r1} by an area of $11\times11=121$~pixels. Therefore, the
difference region {\stf r3} has $2601-121=2480$~pixels in it. For
difference region {\stf r4}, the region of overlap is the bottom left
corner area of region {\stf r2} and still contains 121~pixels. We expect
$961-121=840$~pixels in the differnce region.
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