I1RAY, I2RAY, I3RAY are the returned vertices for each triangle in anticlockwise order. NTRI is the returned number of triangles. The Watson algorithm is used for calculating the Delaunay triangulation. The routine CIRC3P calculates a circle specified by three points. XM, YM are the calculated coordinates of the centre point.
R is the calculated radius of the circle.
This routine is necessary for plotting date labels and data containing date coordinates. IDAY is the day number of the date between 1 and 31. 3 N is the number of days. IDAY is the returned day number. IDAY is the day number of the date between 1 and 31.