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 Pixel scale in mkobjects
   
suma99
 08/24/2015 07:41PM (Read 1105 times)  
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Registered: 08/24/2015
Posts: 4
Hello,

I am wondering how to find the pixel scale from a simulated image of galaxies made on "gallist" and "mkobjects". I had done:
artdata\$this->_split2($m[0]) gallist galaxy.dat
Number of galaxies in the output list (30): 30
artdata\$this->_split2($m[0]) mkobjects galaxy obj=galaxy.dat ncols=1000 nlines=1000

However, I do not see that the header of the fits image that is created specifies what is the pixel scale of the image. How do I find this? Perhaps there a formula I can use to find the pixel scale using the values given in the header of the simulated image?

I have found previously an archive that mentions a little about how to make an image with a pixel scale of 1 arcsec/pixel: https://iraf.net/forum/viewtopic.php?showtopic=127136

It was said that: "For a detector with a pixel scale of 0.1"/pixel and an object
that covers x" on the detector, you should determine how many pixels the
object will cover, and determine the radius from that. This will be the
value you put into the objects file."

However it is not very clear to me and I cannot ask for a clarification since it is a closed thread.


 
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fitz
 08/24/2015 10:27PM  
AAAAA
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Registered: 09/30/2005
Posts: 4040
GALLIST and MKOBJECTS are meant to create images with a specified spatial distribution of galaxies/stars within an image, not necessarily to simulate a telescope/camera configuration which is what defines the plate scale. So, although the sizes and positions are specified in terms of pixels within the image, you can make the scale whatever you like by creating the appropriate WCS in the header. The 'header' parameter can be used to insert a pre-defined header including the WCS (e.g a header such as for the dev$ypix test image).

 
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