Programme: ELLFIT Purpose: Programme fits an ellipse to an user defined bunch of points. Category: ANALYSIS, FITTING, TABLES File: ellfit.c Author: K.G. Begeman Description: ELLFIT will fit an ellipse to an user defined bunch of points. The data set currently displayed will be used. The user can define his points by choosing two contourlevels, in between lying points are taken as points belonging to an arbitrary ellipse (five parameters). The user can remove points with the cursor. Next a least squares fit to these points X(i), Y(i) is done, with an error calculation. If the fit was successfull, the fitted ellipse will be displayed. The results of the ellipse fit are stored in table ELLFIT. Keywords: ** DISPLAY= Display device [DEFAULT_DISPLAY]. ** COLOUR1= RGB intensities for graphics plane which defines the region of interest; only coordinates inside this region will be used for fitting the ellipse [1.0, 1.0, 1.0]. ** COLOUR2= RGB intensities for graphics plane which defines the coordinates which have data values in the range specified with the RANGE= keyword [1.0, 0.0, 0.0]. ** COLOUR3= RGB intensities for graphics plane which allows the user to undefine points selected with the RANGE= keyword [0.0, 1.0, 0.0]. ** COLOUR4= RGB intensities for graphics plane which displays the fitted ellipse [0.0, 0.0, 1.0]. ** PLOT= Plot fitted ellipse [Y]? --------------------------------------------------------- The user can now define the search area, that is the region of interest. Coordinates on the ellipse can only be taken from this region. Next the programme goes into a loop which allows the user to fit as many ellipses as he wants. --------------------------------------------------------- RANGE= Two data values in between which the points on the ellipse are defined. After these have been supplied, the points inside this range are shown on the display. EDIT= Edit points on ellipse? [Y]. The user can remove some of the unwanted points with the cursor. The user can draw polygons on the screen in a similar way as in defining the search area. Any point selected by RANGE= inside a polygon is unselected. ** AUTO= Automatic initial estimates or user supplied [Y]. If AUTO=N, ELLFIT prompts for the initial estimates with the following keyword: INIPAR= Enter initial estimates for RADIUS, INCL, XPOS, YPOS and PA. Next the program will load the positions and do the least squares fitting. In case you want to keep some parameters fixed for your owm special purpose, you should type the appropriate keyword with the desired value (see keyword list below). When you want to free a parameter again, just type the corresponding keyword without any value. ** RADIUS= Semi Major axis of ellipse (arcsec/pixels). ** INCL= Inclination angle of ellipse (degrees). ** XPOS= X position of centre of ellipse (grids). ** YPOS= Y position of centre of ellipse (grids). ** PA= Position of major axis (degrees). --------------------------------------------------------- After the fit the programme will display the results with the corresponding errors and prompt the user whether is should stop or continue. --------------------------------------------------------- CONTINUE= Continue fitting ellipses? [Y]. FILE= Name of file to save fitted results [ellfit.dat]. Updates: Jan 28, 1991: KGB Document created. Jun 23, 1993: KGB Results in GDS table. May 23, 2002: JPT Increased maximum set name length.