noquintic_interp

Non-visibility image algorithms generate the image first in annular sector coordinates and then convert the image to xy coordinates before returning it to the user. The IDL routine TRIGRID is used for the intepolation to the new coordinate system. Quintic polynomial interpolation (the default) sometimes computes negative values for some pixels. Set noquintic_interp to 1, to disable quintic interpolation and use linear interpolation.