I am trying to plot horizontal scans taken from an aerosol lidar system. The raw data is composed of range resolved aerosol density collected at a particular azimuth angle. The range and azimuth data I convert into values of Northing and Easting against which I plot the aerosol data.

If I use the contour plot procedure the data is plotted correctly, but if I use the contour function the same data will generate a qhull error. Is there a difference in how the qhull procedure is called in each routine.