Mars Global Surveyor (MGS) Derived RSS Maps Definitions RSS - Radio Science Subsystem PDS3 DATA_SET_ID = MGS-M-RSS-5-SDP-V1.0 MAP_PROJECTION_TYPE = SIMPLE CYLINDRICAL START_TIME = 1997-09-12T00:00:00 STOP_TIME = 2002-05-27T23:59:59 ==================================================================== PDS4 Collections: ================= data-maps (urn:nasa:pds:mgs-rss:data-maps) Map Projection Information ========================== In the simple cylindrical projection Map Projections - A Working Manual, parallels of latitude and meridians of longitude are straight lines that intersect one another at right angles. Images in this projection are centered on the equator. Map resolution is constant throughout the image, thus increasing distortion away from the poles. The transformation from latitude and longitude (LAT, LON) in degrees to LINE and SAMPLE is given by the following equations. SCALE = MAP_RESOLUTION SAMPLE = SAMPLE_PROJECTION_OFFSET+SCALE*(LON-CENTER_LONGITUDE)+1 LINE = LINE_PROJECTION_OFFSET-SCALE*(LAT-CENTER_LATITUDE)+1 In the above definitions, integral values of LINE and SAMPLE correspond to the center of a pixel, and the top left image pixel has LINE=1 and SAMPLE=1. LAT and LON are the latitude and longitude of a given spot on the surface in degrees. LINE_PROJECTION_OFFSET is the image line number minus one on which the map projection origin occurs. The map projection origin is the intersection of the equator and the projection longitude CENTER_LONGITUDE. SAMPLE_PROJECTION_OFFSET is the sample number minus one on which the map projection origin occurs. CENTER_LATITUDE is the value of the projection latitude in degrees, which is typically the latitude that passes through the center of the projection. CENTER_LONGITUDE is the value of the projection longitude in degrees, which is typically the longitude that passes through the center of the projection. MAP_RESOLUTION number of pixels per degree at the projection origin. The following four keywords are defined in the PDS Data Dictionary, but their usage in Mars Global Surveyor Radio Science image products may be non-standard. In more conventional usage these keywords define the limits of the area covered by the image or map. In Radio Science products, their values are the extremes at the pixel centers. EASTERNMOST_LONGITUDE longitude of the easternmost pixel (center coordinates) in the map or image. WESTERNMOST_LONGITUDE longitude of the westernmost pixel (center coordinates) in the map or image; numerically, always less than EASTERNMOST_LONGITUDE. MINIMUM_LATITUDE latitude of the southernmost pixel (center coordinates) in the map or image. MAXIMUM_LATITUDE latitude of the northernmost pixel (center coordinates) in the map or image; numerically always greater than MINIMUM_LATITUDE. References ========== Davies, M. E., V. K. Abalakin, A. Brahic, M. Bursa, B. H. Chovitz, J. H. Lieske, P. K. Seidelmann, A. T. Sinclair, and Y. S. Tjuflin, Report of the IAU/IAG/COSPAR working group on Cartographic Coordinates and Rotational Elements of the Planets and Satellites: 1991, Celestial Mechanics and Dynamical Astronomy, 53, 377-397, 1992. Snyder, John P., Map Projections -- A Working Manual, U. S. Geol. Surv. Professional Paper 1395, 383p., 1987.