urn:nasa:pds:magellan_gvdr:data_gvdr:gvtidx_sinu 1.0 1.23.0.0 Product_Observational Magellan Mission urn:nasa:pds:context:investigation:mission.magellan data_to_investigation The Magellan Spacecraft Host urn:nasa:pds:context:instrument_host:spacecraft.mgn is_instrument_host Magellan Spacecraft Radar System Instrument urn:nasa:pds:context:instrument:mgn.rdrs is_instrument Venus Planet urn:nasa:pds:context:target:planet.venus data_to_target GVDR 376 5747 Stanford Center for Radar Astronomy gvdr_0001 Table cartography_parameters_to_image_object 0.00 360.00 90.00 -90.00 Sinusoidal 0 Coordinate Pair 18.225 18.225 5.79478 5.79478 -9.1125 9504.3375 Planetocentric 6051.0 6051.0 6051.0 Positive East urn:nasa:pds:magellan_gvdr:document:gvdrsis data_to_document urn:nasa:pds:magellan_arcdr::1.0 data_to_derived_source_product MGN-V-RDRS-5-SCVDR-V1.0 data_to_derived_source_product 10.17189/1522514 GEO gvtidx.tab 1994-05-10T23:12:00.000 Table 0 2178 This file is the tile index, the starting point of all pixel lookup operations. The description below includes a discussion of the organization of an entire GVDR image as well as instructions for use of this file. The GVDR is a pixel-based map product containing scattering properties of the surface of the planet Venus. Each pixel contains a summary of all Magellan observations of surface scattering properties. Since some pixels were observed more than once or in several modes, the amount and type of information available for each pixel is variable. The information for each pixel is stored in four separate files -- one for each unique data type. Each table has a fixed structure. Pixels observed more than once may have multiple entries in some tables; pixels never observed will not appear at all. This arrangement results in efficient storage of pixel data. In addition, solely in the interest of efficient physical access, the pixels are further organized into rectangular tiles. Within each of the four tables, all the pixels from a given tile are stored in consecutive rows. The storage order of both pixels within tiles and tiles within the entire image is row-major, or scanline format. All the pixels in the upper left tile are stored first, then all the pixels in the tile to its right, and so on. This scheme ensures that pixels located near one another on the planet are stored together in the data file. Two index files provide the row numbers of the observations corresponding to a given pixel. The GVTIDX, or tile index file, tells the rows at which each tile begins in the other files, and the GVPIDX, or pixel index file, tells where each pixel begins relative to the start of its tile. The procedure for finding all observations associated with a given pixel is the following: 1. Determine which tile the pixel belongs to using the tiling information in the GVHDR file. 2. Look up the tile in the GVTIDX file (the two-dimensional array of tiles is stored in row-major, or scanline, order). Obtain the starting rows of this tile in the other five files: GVPIDX, GVXIF, GVRDF, GVADF, and GVANF. 3. Look up the pixel in the GVPIDX file, using the row number just found in the GVTIDX file as the address of the first pixel within the tile. Within each tile, the pixels are also stored in row-major, or scanline, order. 4. The entries in the row of the GVPIDX table are the starting rows and number of rows in the four data files: GVXIF, GVRDF, GVADF and GVANF. The starting rows in the GVPIDX file are relative to the tile starting rows obtained from the GVTIDX file, so add these two numbers together. 5. Look up the rows within the data files themselves. All of this is done automatically by the software provided in the SOFTWARE directory. 9 0 36 Pixel Tile Start 1 1 UnsignedMSB4 4 The row in the GVPIDX file containing the first pixel in this tile, with the first row numbered as 0. This will be a multiple of the number of pixels in a tile, since tiles are either written in their entirety to the pixel index file or not written at all. XIF Tile Start 2 5 UnsignedMSB4 4 The row in the GVXIF table containing the first sample of the first pixel in this tile, with the first row numbered as 0. RDF Tile Start 3 9 UnsignedMSB4 4 The row in the GVRDF table containing the first sample of the first pixel in this tile, with the first row numbered as 0. ADF Tile Start 4 13 UnsignedMSB4 4 The row in the GVADF table containing the first sample of the first pixel in this tile, with the first row numbered as 0. ANF Tile Start 5 17 UnsignedMSB4 4 The row in the GVANF table containing the first sample of the first pixel in this tile, with the first row numbered as 0. XIF Tile Samples 6 21 UnsignedMSB4 4 The number of rows in the GVXIF table that correspond to pixels within this tile. The first such row is numbered 'XIF Tile Start', and the last such row is numbered 'XIF Tile Start' + 'XIF Tile Samples' - 1. RDF Tile Samples 7 25 UnsignedMSB4 4 The number of rows in the GVRDF table that correspond to pixels within this tile. The first such row is numbered 'RDF Tile Start', and the last such row is numbered 'RDF Tile Start' + 'RDF Tile Samples' - 1. ADF Tile Samples 8 29 UnsignedMSB4 4 The number of rows in the GVADF table that correspond to pixels within this tile. The first such row is numbered 'ADF Tile Start', and the last such row is numbered 'ADF Tile Start' + 'ADF Tile Samples' - 1. ANF Tile Samples 9 33 UnsignedMSB4 4 The number of rows in the GVANF table that correspond to pixels within this tile. The first such row is numbered 'ANF Tile Start', and the last such row is numbered 'ANF Tile Start' + 'ANF Tile Samples' - 1. gvtidx.lbl 0 PDS3 Original PDS3 label Carriage-Return Line-Feed gvtidx.fmt 0 PDS3 Original PDS3 format file Carriage-Return Line-Feed