How accurate is the pointing information?
CDS uses its offset pointing system (OPS) to move to any location within range. This pointing has an rms of 5″ or better . When a dataset is read in using readcdsfits the pointing values in the QLDS are updated according to current knowledge of the spacecraft pointing – see Software Note #48 ( PostScript 87 Kb ) The reliability of the pointing has been checked from the year 2000 synoptic North limb rasters. The distribution of residuals of the observed limb from the calculated one is shown here . In the upper plot some large negative residuals are present, but checking the raw data reveals that these result from corruption of the OV limb data by filaments. The lower distribution ignores those values and confirms that there has been no degradation in the pointing which in one dimension has an rms of less than 3″. The extent of the CDS pointing capability (its Field Of View – FOV) can be seen using • IDL> cdsfov, x, y where x and y can be arrays of Solar (X,Y) locations (arcsecs from dis
