CCSD3ZF0000100000001NJPL3IF0PDS200000001 = SFDU_LABEL RECORD_TYPE = STREAM PRODUCT_CREATION_TIME = 1992-08-01 OBJECT = TEXT NOTE = "Notes on using the geometry tables." END_OBJECT = TEXT END NOTES ON USING THE GEOMETRY TABLES The table and label files located in the GEOMETRY directory contain information describing the primary viewing geometry elements (SPICE) of the Viking EDR frames that make up the Mars color MDIM image files. They were derived photogrammetrically as a by-product of color MDIM compilation, and supercede data originally provided by the Mission Test and Imaging System (MTIS) during active flight operations. All geometry elements are in the EME1950 coordinate system, the coordinate system originally used by the Viking Project. Each row (record) in the tables correspond to an EDR image, the columns (fields) in each row give the primary geometry elements as four vectors: Camera-Angles (declination, right-ascension, twist), Planet-Angles (declination, right-ascension, and spin), Spacecraft Vector, and Sun Vector. Each record consists of 196 bytes, with a carriage return/line feed sequence in bytes 195 and 196. All fields (columns) are separated by commas, and character and time fields are enclosed in double quotation marks. This format allows the table to be treated as a fixed-length record file on hosts that support this file type and as a normal text file on other hosts. The MDIMGEOM.TAB gives the EDR images uses in the MDIM compilation. The format of the tables are given below. FORMAT OF GEOMETRY FILES ------------------------ Byte Positions Description --------------------------------------------------------------------- 2 - 7 IMAGE_ID: this field is a six-character string to identify a Viking Orbiter image. The first three characters represent the orbit number. The fourth character is either an A for Viking Orbiter 1, a B for Viking Orbiter 2, or an S for the Viking Orbiter 1 Survey Mission. The letters C and D is used for images acquired by Viking Orbiter 1 and 2, respectively, before orbit insertion. The letter X is used for Viking Orbiter 1 images when more than 100 images were taken in one orbit. The last two characters represent the sequence number of the image within that orbit. 10 - 19 IMAGE_NUMBER: The image number is a value derived from the spacecraft clock start count. It is also known as the FSC (frame start count), and is a commonly used identifier for a Viking Orbiter image. 21 - 32 Camera angle - declination in (degrees) EME1950 34 - 44 Camera angle - right ascension (degrees) EME1950 46 - 56 Camera angel - twist (degrees) EME1950 58 - 65 Spacecraft to target X-component vector EME1950 67 - 74 Spacecraft to target Y-component vector EME1950 76 - 83 Spacecraft to target Z-component vector EME1950 85 - 93 Planet angles - declination (degrees) EME1950 95 -103 Planet angles - right ascension (degrees) EME1950 105 -113 Planet angles - spin EME1950 115 -126 Sun to target X-component vector (EME1950) 128 -139 Sun to target Y-component vector (EME1950) 141 -152 Sun to target Z-component vector (EME1950) 154 -168 Julian day when the image was acquired. 171 -193 The time when the image was acquired, in the format yyyy-mm-ddThh:mm:ss.ssZ. 'yyyy' = year, 'mm' = month, 'dd' = day of month, 'hh' = hour, 'mm' = minute, 'ss.ss' = seconds. The time system is Universal Time (UTC).