wiki:WKTRaster/RFC/RFC2_V0WKBFormat

RFC2: Well Known Binary format for RASTER type

Author: Sandro Santilli <strk@…>
Date: 2009-01-29
Status: Adopted

Revisions
2011-01-24 by Jorge Arévalo
  • Adds isNodataValue bit to band flags

The WKB format for RASTER is meant for transport. Takes into account endiannes and avoids any padding. Still, beside padding and endiannes, it matches the internal serialized format (see RFC1), for quick input/output.

Basic Type definitions

  • byte: 1 byte
  • uint16: 16 bit unsigned integer (2 bytes)
  • uint32: 32 bit unsigned integer (4 bytes)
  • float64: double precision floating point number (8 bytes)
name type meaning
endiannes byte 1:ndr/little endian 0:xdr/big endian
version uint16 format version (0 for this structure)
nBands uint16 Number of bands
scaleX float64 pixel width in geographical units
scaleY float64 pixel height in geographical units
ipX float64 X ordinate of upper-left pixel's upper-left corner in geographical units
ipY float64 Y ordinate of upper-left pixel's upper-left corner in geographical units
skewX float64 rotation about Y-axis
skewY float64 rotation about X-axis
srid int32 Spatial reference id
width uint16 number of pixel columns
height uint16 number of pixel rows
bands[nBands] RASTERBAND Bands data

Band

name type meaning
isOffline 1bit If true, data is to be found on the filesystem, trought the path specified in RASTERDATA
hasNodataValue 1bit If true, stored nodata value is a true nodata value. Otherwise the value stored as a nodata value should be ignored.
isNodataValue 1bit If true, all the values of the band are expected to be nodata values. This is a dirty flag. To set the flag to its real value the function st_bandisnodata must must be called for the band with 'TRUE' as last argument.
reserved 1bit unused in this version
pixtype 4bits 0: 1-bit boolean 1: 2-bit unsigned integer 2: 4-bit unsigned integer 3: 8-bit signed integer 4: 8-bit unsigned integer 5: 16-bit signed integer 6: 16-bit unsigned signed integer 7: 32-bit signed integer 8: 32-bit unsigned signed integer 9: 32-bit float 10: 64-bit float
nodata 1 to 8 bytes depending on pixtype [1] Nodata value
data RASTERDATA Raster band data (see below)

Band data (in-db)

name type meaning
pix[w*h] 1 to 8 bytes depending on pixtype [1]

Pixels values, row after row, so pix[0] is upper-left, pix[w-1] is upper-right.

As for endiannes, it is specified at the start of WKB, and implicit up to 8bits (bit-order is most significant first)

[1] 1,2 and 4 bit pixtypes are still encoded as 1-byte per value

Band data (out-db)

name type meaning
bandNumber int8 0-based band number to use from the set available in the external file
path string null-terminated path to data file
Last modified 7 years ago Last modified on Jan 25, 2015, 10:57:31 AM