WFPC2 Image Display FAQs

Q: How do I make a mosaic of all four WFPC2 chips?

A: The 'wmosaic' task in STSDAS can be used to make mosaics of both WFPC2 and WF/PC-1 data. The task takes into account chip distortions and rotations, and also scales the PC to the same resolution as the WF chips for WFPC2 images. Note that the 'wmosaic' task in earlier versions of STSDAS will only work for WF/PC-1 images, and should NOT be used on WFPC2 images.

Q: How do I convert pixel coordinates to RA and DEC?

A: The 'metric' task in STSDAS can be used to get RA and DEC values from pixel coordinates. This task takes into account chip distortions and rotations when calculating RA and DEC, and will work for both WFPC2 and WF/PC-1 images. Note that the 'metric' task in earlier versions of STSDAS will only work for WF/PC-1 images, and should NOT be used on WFPC2 images.

Q: How do I find out the orientation of my WFPC2 image on the sky?

A: Two tasks in STSDAS can accomplish this. The task 'north' in the 'stsdas.hst_calib.ctools' package will print the position angle of the image. The task 'compass' in the package 'stsdas.graphics.sdisplay' will draw north and east arrows on your image.

Q: Is it possible to overplot a coordinate grid on my image?

A: Yes, the task 'disconlab' in the 'stsdas.graphics.sdisplay' package allows you to do this.

Q: How do I overplot the WFPC2 field of view on a non-WFPC2 image?

A: The the task 'siaper' in the 'stsdas.graphics.stplot' package allows you to plot a given HST aperture on a display on top of an arbitrary image. The DSS web page will allow you to overplot the HST FOV on a GIF image of a DSS image. See http://archive.stsci.edu/dss/. This can also be done via the DSS search screen in xstarview. From the main screen click on "Non-HST Data Searches".