Table of Contents
RA_ERR and DEC_ERR values near poles
The RA_ERR and DEC_ERR values are approximations and become increasing inaccurate the closer to the poles, DEC=+/-90.
Users may also see incorrect values for these errors for RA values very near 0|360 such that the error bar crosses the boundary and wraps around.
The X_ERR and Y_ERR values in physical pixels is correct. Users can use these together with the known plate scale to compute their own error estimates.
vtpdetect with negative coordinates (16 May 2007)
Running vtpdetect on a level 1 event file may fail with an error that all the events are at the same location and the tool cannot tessellate. This is related to the (normal) bad coordinates at the beginning of the ObsID where there is no aspect data.
If you must work with the evt1.fits file, apply a time filter before running vtpdetect.