[Gdal-dev] +proj=ob_tran equivalent, rotation

[Kovacs Baldvin]

Hi!

I tried to warp a raster image being in latlong representation
into some projected systems like Aitoff, but the world being
rotated, the poles being not at the center of the top of the
projection.

In proj4 you can use +ob_tran +o_lon_p=0 +o_lat_p=0 +proj=anything
to achieve this.

However, since OGRSpatialReference reimplements (a subset of)
the proj parameter parsing, +ob_tran is not available.

My questions:

- is my goal somehow simply achievable, just I can't figure how?
  If so, please show me how!

- if it is not:

  Basically what happens is that when I give gdalwarp a proj4
  projection definition, it parses it, then it stores it in
  a tree similar to the strukture of WKB. It gives the
  WKB to a function which in turn converts it back to proj4,
  and then initializes the proj4 projection objects with that
  string.

  I tried to manually intervene into the last step, and I
  succeded, I achieved my goal.

  Now I am planning to create a patch that makes OGRSpatialReference
  similar to a Perl scalar variable: When it is initialized with
  a proj4 definition, it keeps that definition, and uses that if
  only that is needed. However, when something else is also needed,
  OGRSpatialReference automatically coerces itself into the 
  tree representation.

  The goal is to achieve that through a simple gdalwarp session
  OGRSpatialReference should be happy with either representation,
  which makes it possible to use any proj4 projections. (I
  beleive it is always a design flaw to reimplement an interface
  of a library, sync keeping in sync the features is not a possible
  task to do.)

  I am curious about your views on these things.

Best regards,
Baldvin Kovacs