how to plot a surface map with rectangular pixels ?
nelly wrote on Feb 18, 2009
I am trying to plot a radiance map, with a pixel size of 0.5" by 0.33".
Is there any option where to give the size of the pixel?
When I create the .imh image, and then convert it to .fits, it is directly generated with a square pixel. I didn't find anyway to do it otherwise.
I tried 'imlintran', which is supposed to do a certain scaling, but the pixel stays a square no matter what.
If you have any hint, please let me know.
Thanks
Nelly
Is there any option where to give the size of the pixel?
When I create the .imh image, and then convert it to .fits, it is directly generated with a square pixel. I didn't find anyway to do it otherwise.
I tried 'imlintran', which is supposed to do a certain scaling, but the pixel stays a square no matter what.
If you have any hint, please let me know.
Thanks
Nelly
Mike Fitzpatrick wrote on Feb 18, 2009
Sorry, but there is no concept of physical pixel size in the image. The best you could do would be to create a plot with an aspect ratio representing the physical area on the sky being plottted. For example, if your image were 1000x1000 then you could use the MAGNIFY task to scale it to 660x1000 (with flux conservation enabled) and the image would represent a 330" square area on the sky.
It is also possible to create a graphcap entry so a plot window or hardcopy device has a specific aspect ratio and you wouldn't need to modify the image directly, but note this won't help with analysis. If what you're really trying to do is compute the flux/area on the sky you'll need to scale. Hope this helps, perhaps others will have suggestions as well.
Cheers,
-Mike
It is also possible to create a graphcap entry so a plot window or hardcopy device has a specific aspect ratio and you wouldn't need to modify the image directly, but note this won't help with analysis. If what you're really trying to do is compute the flux/area on the sky you'll need to scale. Hope this helps, perhaps others will have suggestions as well.
Cheers,
-Mike
nelly wrote on Feb 18, 2009
Hi Mike,
Thanks for your answer, it definitely helps to know it is not possible to have rectangular pixels with iraf.
Thanks for your tip. I tried MAGNIFY quickly, and it might be the only option to use for scaling, however the pixel size doesn't get scaled itelf unfortunately.
I only need the scaling for the plot itself and not the flux.
I look into this tool more carefully, and will let you know how it works.
I might end up using another tool for plotting, but I still haven't found an adequate one. MATLAB might be an option ...
Nelly
Thanks for your answer, it definitely helps to know it is not possible to have rectangular pixels with iraf.
Thanks for your tip. I tried MAGNIFY quickly, and it might be the only option to use for scaling, however the pixel size doesn't get scaled itelf unfortunately.
I only need the scaling for the plot itself and not the flux.
I look into this tool more carefully, and will let you know how it works.
I might end up using another tool for plotting, but I still haven't found an adequate one. MATLAB might be an option ...
Nelly
Last post on Feb 18, 2009