reswcs - reset the WCS keywords in an image header to a TAN projection
reswcs image
- image = "" [file name]
- The name of an input image file which is to have its header updated in situ.
This task exists to transform the headers of images, typically created by the EIS drizzling software, so that they have conventional and convenient WCS (world coordinate systems) in their headers. This eases the use of such images in other external packages.The input images must have either TAN (tangent plane) or COE (conic equal are) projection types. This task uses the existing WCS to find the position on the sky of the centre of the frame. It sets the new CRPIX1/CRPIX2 to be this centre point and writes the appropriate CRVAL1/CRVAL2. It then finds the increments in X and Y on the sky caused by shifting a pixel in X or Y on the input away from the centre. These values are then used to update the CD matrix in the output. The output image is in TAN projection with the reference pixel at the centre.
The original WCS (CRVAL1/2, CRPIX1/2, CD1/2_1/2, CTYPE1/2) are copied to header keywords with names OCRVAL1,OCRVAL2 etc.
If the image "test.hhh" has been produced by the EIS drizzle and has a COE WCS with reference point far outside the frame. The WCS can be reset to a more convenient representation of a TAN projection with the reference pixel at the centre with the command:The header update will be done in situ.reswcs test.hhh
It only takes a very short time.
drizzle,parapredriz,coe2eq,eq2coe