[Gdal-dev] Affine Transformation and Calibration Equation for Maptech/BSB format

[Christopher Barker]

Frank Warmerdam wrote:
> Internally GDAL can compute 2nd order polynomial warp
> equations from the reference points and this is what I
> generally encourage people to use (via gdalwarp) to
> convert the images to a nice "north up" image.


> But, in
> fact, I presume the files are actually normally in a mercator
> projection and that we would be even better off to work out
> the details of that and then use proper reprojection to get
> to other coordinate systems.

Hi Frank,

This is what I was referring to last week when I said goodbye. Yes, 
almost all NOAA charts are Mercator (they may be a few that aren't near 
the poles). It appears to be a limitation in the BSB drivers that the 
projection info isn't picked up. Everything needed is in the text header 
of the BSB files, so it shouldn't be hard to do.

That being said, a 2nd order polynomial fit to the GRPs is probably good 
enough for most uses -- but I'm a purist.

I've been hoping for a while to dig into this and try to fix it, but 
haven't had a chance yet. If anyone else does, I'd be glad to do a lot 
of testing -- I should be able to get ALL the NOAA charts here, and run 
tests against them.

-Chris


-- 
Christopher Barker, Ph.D.
Oceanographer

Emergency Response Division
NOAA/NOS/OR&R            (206) 526-6959   voice
7600 Sand Point Way NE   (206) 526-6329   fax
Seattle, WA  98115       (206) 526-6317   main reception

Chris.Barker at noaa.gov