[daip] aips question

[Eric Greisen]

Ashley King wrote:
> Hi,
> 
> I am having a problem where I'm finding it difficult to convert the X 
> axis pixel scale from an IMAGR output to the correct RA. The Y axis 
> pixel scale appears to be fine.
> 
> I find in my images, that the distance between two knots in RA is about 
> 2e-4 seconds, which I convert to arcsecs to 3e-3''. However the distance 
> between the knots in the X-direction is 30 pixels which the pixel scale 
> i used to make the image is 4e-5 arcsecs, which corresponds to 1.2e-3. 
> It seems that I am off by almost a factor of pi. Is this a  known 
> problem with aips or am I converting between RA and arcsec wrong.

The increment in RA is the increment in arc seconds divided by 
cos(declination).  Try TVLOD and then point at the two objects in the 
verb IMXY.

ERic Greisen