[raster] document ST_PixelWidth and ST_PixelHeight

[dzwarg]

These are in trunk, need documentation.

[bnordgren]

It would be very helpful to include a figure.

Depending on how in depth you want to go, there are images of typeset equations (justifying this picture) on DevWikiRealParameters.

• Width : "Pixel size in the i direction"
• Height: "Pixel size in the j direction"

Note that the terms "width" and "height" may or may not be clear. After all, rotate 90 degrees (perfectly legal) and "width" becomes "height".

[bnordgren]

Source of the illustration (openoffice drawing document)

[robe]

done at r8301 and I incorporated the image in ST_PixelWidth.

Ideally we should have a chapter on raster fundamentals and best practices that covers these things in more detail and that is linked back to from the reference functions.

Something similar to  http://www.postgis.org/documentation/manual-svn/using_postgis_dbmanagement.html (primary importance)

and -  http://www.postgis.org/documentation/manual-svn/ch05.html (secondary).

Where we would stuff raster concepts / best practices etc. I was thinking about putting it in those existing sections, but I think that may just confuse people not using raster and force people looking for raster information to sift through stuff that is only useful if you are doing strictly geometry. Raster is dfferent enough that it deserves its own chapters and we rename the existing Data Management for Geometry/Geography? etc. Granted there is some overlap, but that overlap is probably better served in a raster section with reference to it from the geometry section.

[robe]

feel free to reopen if you think further changes are required