Known Issues (Pending Validation)

Below is a list of known issues with STIPS that are pending validation. Items will be removed from this list as they are addressed in future STIPS updates.

  • The orientation of the image is non-standard, with east pointing to the right of the image. The relative position of sources is not affected.

  • There exists a function to place extended sources given a set of Sersic parameters, but its validity and functionality have not been tested.

  • The flux measurements of sources are only validated in the absence of noise/background. As such, the net flux of the image may be inaccurate.

  • STIPS interpolates nine PSFs generated by STPSF across the detector to the location of the source being placed. However, there is currently a known offset of 20 pixels (in both the X and Y directions) between the location at which the PSF is interpolated, and the location at which the target is displayed. The header of the output image lists both of these locations: ‘x’ and ‘y’ for the location at which the PSF is interpolated and ‘x_input’ and ‘y_input’ for the location at which the target is displayed.

    Note

    This does not affect the target position or center on the detector. It only means that, if a point source is created with a position of (x, y), it will be placed at location (x, y) but the interpolated PSF shape will be the shape of the PSF at location (x+20, y+20). Because the WFI PSF shape does not vary strongly over this distance, the effect is minimal and should not be a concern for most science cases. If ultra-precise PSF models are required, the user should generate them directly with STPSF at the desired pixel location.

  • Bright sources will have large diffraction spikes that are visible beyond 22 pixels away from the center of the source. A psf_bright_limit and psf_xbright_limit (extra-bright limit) magnitude can be specified –– objects brighter than this threshold will be computed out to a radius of 44 (bright) and 88 (extra-bright) pixels, respectively. Note that, because point source flux is computed for every pixel, bright targets will take roughly four times as long (and extra-bright sources 16 times as long) to compute as standard sources, so these limits should only be set when it matters.

  • The STIPS star generation sub-module (stips.star_generator) depends on the esutil Python module. This module can currently be installed as part of a Conda environment, but can’t be installed in a working state from a pip/setup environment. As such, if you are installing STIPS without using Conda, and you need to use the star generation sub-module, you will have to make an additional step. After installing STIPS, but before using it, install esutil using pip without using a local cache (i.e. run pip install esutil --no-cache-dir).

If you encounter any issues not listed here, please see the help page.