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May 18, 2018, 2:46:41 AM5/18/18
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If I upload a black and white image with stars replaces with single white pixels nova.astrometry.net returns an axy.fits (Stars detected in your images x,y table) that looks something like this:
...
...
265.9551 79.0449 9.0074 0
101.9551 159.9551 9.0074 0
247.0449 225.0449 9.0074 0
121.0449 259.0449 9.0074 0
...
I expected all pixel coordinates (columns 1,2) to all end with *.5,*.5 or all end with *.0,*.0.
It looks like they are all close to *.0,*.0 but +-0.05, which is a bit unusual and perhaps sometimes significant.
Personally I prefer the coordinate system, that has image pixel corners falling on round integers and pixel centres ending with 0.5,0.5 because that coordinate system has a lot of natural advantages, but that's another story....
However it may be useful to let users know when they upload their own x,y tables that they must assume that the [left,top] image pixel centre falls on [1,1] and the [left,top] corner of that pixel at [0.5,0.5].
Perhaps it is already mentioned and I am blind... if so my apologies.
I know that I can simply upload my own x,y table, but I wanted to test is source extractor behaves sensibly on simple data.
Here is the full table:I expected all pixel coordinates (columns 1,2) to all end with *.5,*.5 or all end with *.0,*.0.
It looks like they are all close to *.0,*.0 but +-0.05, which is a bit unusual and perhaps sometimes significant.
Personally I prefer the coordinate system, that has image pixel corners falling on round integers and pixel centres ending with 0.5,0.5 because that coordinate system has a lot of natural advantages, but that's another story....
However it may be useful to let users know when they upload their own x,y tables that they must assume that the [left,top] image pixel centre falls on [1,1] and the [left,top] corner of that pixel at [0.5,0.5].
Perhaps it is already mentioned and I am blind... if so my apologies.
I know that I can simply upload my own x,y table, but I wanted to test is source extractor behaves sensibly on simple data.
168.7822 285.7421 9.0089 0
164.1106 279.2492 9.0089 0
343.9551 3.2671 9.0074 0
233.0449 19.9551 9.0074 0
119.9551 87.0449 9.0074 0
459.9551 227.0449 9.0074 0
145.9551 431.0449 9.0074 0
301.9551 439.9551 9.0074 0
265.9551 79.0449 9.0074 0
101.9551 159.9551 9.0074 0
247.0449 225.0449 9.0074 0
121.0449 259.0449 9.0074 0
411.0449 391.9551 9.0074 0
221.0291 477.9392 9.0074 0
57.0449 471.0449 9.0074 0
197.0449 115.0449 9.0074 0
29.0449 179.0449 9.0074 0
241.0449 245.9551 9.0074 0
137.0449 291.0449 9.0074 0
215.9633 467.9674 9.0074 0
119.0449 543.9551 9.0074 0
257.0449 141.0449 9.0074 0
177.9551 305.9551 9.0074 0
187.0449 513.0449 9.0074 0
21.0449 565.9551 9.0074 0
175.9551 169.9551 9.0074 0
209.0449 381.9551 9.0074 0
289.0449 533.9551 9.0074 0
91.0449 603.0449 9.0074 0
201.9551 173.0449 9.0074 0
265.0429 579.9526 9.0074 0
261.0458 567.9569 9.0074 0
Best regards and thank you,
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