MAPFILES

(Compiled by TC)

Description

MAPFILES is the directory that contains all of the maplets and bigmaps that have been created. Mapfiles contain a short header (below) that outlines basic information about the maplet (half-size, scale, central vector, coordinate frame) as well as the height and albedo values for each maplet pixel.

The mapfile is made up of 72 byte records. The first record contains information describing the size, scale, orientation and position of the map:

• bytes 1-6 Unused
  bytes 7-10 Scale in km/pixel (real*4 msb)
  bytes 11-12 qsz where map is 2*qsz+1 x 2*qsz+1 pixels (unsigned short lsb)
  bytes 16-27 map center body fixed position vector in km 3 x (real*4 msb)
  bytes 28-39 Ux body fixed unit map axis vector 3 x (real*4 msb)
  bytes 40-51 Uy body fixed unit map axis vector 3 x (real*4 msb)
  bytes 52-63 Uz body fixed unit map normal vector 3 x (real*4 msb)
  bytes 64-67 Hscale = maximum abs(height)/30000 (real*4 msb)*
  byte 13255* X position uncertainty unit vector component (byte) +
  byte 14255* Y position uncertainty unit vector component (byte) +
  byte 15255* Z position uncertainty unit vector component (byte) +
  bytes 68-71 magnitude of position uncertainty (real*4 msb) +
  byte 72 Unused
  

* heights are in units of map scale + these are pretty much unused as far as I can see.

The remaining records are made up of 3 byte chunks:

• bytes 1-2 height/hscale (integer*2 msb)
  byte 3 relative "albedo" (1-199) (byte)

If there is missing data at any point, both height and albedo are set to zero.

Example of a MAPFILE Header

 # Qsize           49
 # Scale    9.9999997473787516E-006
 # Vector   -2.6262991130352020E-002  0.26271706819534302       -3.1600955873727798E-002
 # Ux    6.2937657348811626E-003 -0.13774713873863220      -0.99044746160507202     
 # Uy  -0.99829435348510742       -5.8354031294584274E-002   1.7719966126605868E-003
 # Uz   -5.8040685951709747E-002  0.98874694108963013      -0.13787946105003357