quickfit -- Fit an ellipse to the limb for a full disk scan
- Name of image to be fit.
- threshold = 4
- Squibby brightness threshold to use in determining limb points.
- xguess = 1024
- X coordinate of center of first guess circle.
- yguess = 1024
- Y coordinate of center of first guess circle.
- halfwidth = 50
- Halfwidth of window centered on previous limb point to search through for a limb point on the current line.
- rowspace = 20
- Number of rows to skip between limbpoints near center in y.
- rejectcoeff = .02
- Least squares rejection coefficient. If radius of a limbpoint is more than this far from the limb, where limbradius = 1.0, it is not used in the fit.
Quickfit finds the least squares best fit ellipse to the limb in a full disk scan. Quickfit returns the ellipse parameters (x,y coordinates of the ellipse center and the x and y semidiameters), the number of limbpoints found, the number of limbpoints rejected, and the fraction of limb points rejected by the least squares routine. This fraction rejected allows the user to determine to some extent the goodness of the data and allows him or her to rerun Quickfit with different parameters to take this goodness into account. Quickfit also returns the sub-earth latitude and longitude when in verbose mode. The ellipse and ephemeris parameters are stored in the image header for future reference.
1. To find the best fit ellipse for the limb in an image called "image1" and to see verbose output, one would use the following command:
vt> quickfit image1 v+
This will also use the default values of rowspace, halfwidth, and rejectcoeff.