[postgis-devel] [WKT Raster] Regular blocking and null extent

[Mateusz Loskot]

Hi,

Would like to clarify the regular blocking parts of the specification [1].

[1] http://trac.osgeo.org/postgis/wiki/WKTRaster/SpecificationWorking01

The extent field of RASTER_COLUMNS table is specified as:

"a polygon geometry containing all raster tiles, or NULL if predefined
bounds are not known. For "regular_blocking" cases this geometry will be
a simple rectangle. In other cases it might be an irregular polygon."

Shouldn't "will be" read "must be"?

Later in the specification:

"If the regular_blocking field is true
...
5. The extent field must be a simple rectangle (non-rotated)."

So, point 5 defines following assumptions:
* for regular_blocking, non-NULL extent must be specified
and
* specified extent must be non-rotated rectangle.

Certainly, if regular blocking coverage is empty, dimensions of extent
rectangle are equal to Zero. 0

Is that correct?

Shall we allow generation of regular blocking tables
from non-georeferenced datasets reported by GDAL as follows:

$ gdalinfo chessboard-64x64.tif 
Driver: GTiff/GeoTIFF
Files: chessboard-64x64.tif
Size is 64, 64
Coordinate System is `'
Metadata:
  TIFFTAG_DOCUMENTNAME=/home/mloskot/data/test/sample/chessboard-64x64.tif
  TIFFTAG_IMAGEDESCRIPTION=Sample 4-fields greyscale chessboard
  TIFFTAG_XRESOLUTION=72
  TIFFTAG_YRESOLUTION=72
  TIFFTAG_RESOLUTIONUNIT=2 (pixels/inch)
Image Structure Metadata:
  INTERLEAVE=BAND
Corner Coordinates:
Upper Left  (    0.0,    0.0)
Lower Left  (    0.0,   64.0)
Upper Right (   64.0,    0.0)
Lower Right (   64.0,   64.0)
Center      (   32.0,   32.0)
Band 1 Block=64x64 Type=Byte, ColorInterp=Gray

and assume pixelsize_x = 1 and pixelsize_y = -1 ?


Best regards,
--
Mateusz Loskot
Senior Programmer, Cadcorp
http://www.cadcorp.com