The calibrated magnetogram images (the mag product) input to MAGMAP are processed into Carrington coordinates by first running EPHEMINTERP to calculate the value of L0, the center of the image in heliographic coordinates. The images are then processed through CAMOFFSET to calculate the camera offset angle and are then processed through HGREMAP with the proper plm_trim file to produce images registered in heliographic coordinates with a size of 256x256 pixels. The images produced by HGREMAP are registered in heliographic coordinates and represent the surface of the sun from -90° to 90°. A template image with a size of 512x256 is created. The template image is zeroed and the image produced by HGREMAP is placed in the center of the grid. The image is then shifted using SHIFTLINES and the value of L0 to the proper place in the template image.
A maq FITS image file consists of 512x256 16-bit integer pixels containing magnetic field strength in arbitrary units.
The heliographic longitude is (ix-1)*359.0/511.0 + 0.5 where ix is the one-indexed pixel address. The sin of the heliographic latitude is (iy-1)*2.0/255.0 - 1.0 where iy is the one-indexed pixel address.MAGMAP adds the following parameters to the FITS header: B0, L0, P_ANGLE, SEMIDIAM, OFFSET.
If the polarity of the magnetogram is inverted, a line similar to
GHIST018= 'ctmag960427t1541 , *, -1, ctmag960427t1541'appears near the end of the header.
From the start of network operations until the present (9801120), the magnetograms from the Cerro Tololo, Udaipur, and Mauna Loa sites are being corrected for a polarity difference. The images are inspected using a movie tool and the bad images are logged and then deleted. The images from the Mauna Loa site that were acquired before the replacement of the pre-filter in February 1996 were completely removed.