Projecting coordinates to Albers Equal-Area Conic

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Projecting coordinates to Albers Equal-Area Conic

Blake Willmarth
Hi all, I'm new to geoprocessing and C in general.

The Plan: Get coordinates from a shapefile and look up their values in a geotiff image. Both use datum GCS_NAD83, the tiff is projected in Albers Equal-Area Conic (both use ellipsoid GRS 1980).

The problem is the coordinates are coming out in degrees and I need to project them to Albers meters in order to look up the tiles - it's simply(?) a matter of converting the units. Is there a way to do this in libgeotiff or do I have to use another library, such as PROJ.4?

Thank you for your time.

Blake

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Re: Projecting coordinates to Albers Equal-Area Conic

Frank Warmerdam
Blake Willmarth wrote:

> Hi all, I'm new to geoprocessing and C in general.
>
> The Plan: Get coordinates from a shapefile and look up their values in a
> geotiff image. Both use datum GCS_NAD83, the tiff is projected in Albers
> Equal-Area Conic (both use ellipsoid GRS 1980).
>
> The problem is the coordinates are coming out in degrees and I need to
> project them to Albers meters in order to look up the tiles - it's
> simply(?) a matter of converting the units. Is there a way to do this in
> libgeotiff or do I have to use another library, such as PROJ.4?

Blake,

This is not a simple conversion of units.  The transformation between
projected (albers meters) and geographic (lat/long degrees) is non-linear
and needs to be done using a projections library like PROJ.4.  PROJ.4
should be fairly easily used in combination with libgeotiff and you can
see some example use in the bin/listgeo.c utility.

Best regards,
--
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I set the clouds in motion - turn up   | Frank Warmerdam, [hidden email]
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