[Gdal-dev] Newbie question

s duclos sylvain_duclos at yahoo.com
Fri Mar 21 10:47:39 EST 2003

--- Frank Warmerdam <warmerdam at pobox.com> wrote:
> Charlie Van Dusen wrote:


> Most (all?) BSB charts uses a set of control points,
> and often they don't
> desribe a perfect north up coordinate system.  I
> don't know if this is because
> they are produced by scaning charts or what.

I'm maybe late on this ... 

If the BSB chart is a mercator then the convention
is north up.

I'm not mutch into BSB so maybe when you say
"don't desribe a perfect north up" 
you mean that in a mathematical sens.

But if you mean that the error is greater then
what should be expected then a think there is

I think that CHS paper chart are printed from NTX
data format. Don't know how this data is translated
to BSB thought.


> The solution is to resample the charts into a north
> up coordinate system.
> The simpliest way to do this is something like:
> gdalwarp 999501.KAP 999501.tif
> This basically warps the chart based on it's control
> points.  The
> transformation in minimal in most cases, but the
> result is a perfectly
> north-up image that ArcExplorer can hopefully
> process.
> The caveat is this, the gdalwarp program (till this
> afternoon) did not
> copy a color table to the output file.  I have
> corrected this in CVS.
> If you are up to building GDAL yourself, you should
> be able to grab
> the CVS snapshot tomorrow, build from source, and
> then use gdalwarp.
> Otherwise you will have to wait for the next binary
> release.  I have
> no fixed timetable for that.
> Best regards,
> -- 
> I set the clouds in motion - turn up   | Frank
> Warmerdam, warmerdam at pobox.com
> light and sound - activate the windows |
> http://pobox.com/~warmerdam
> and watch the world go round - Rush    | Geospatial
> Programmer for Rent
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