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)

Header

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