[Gdal-dev] Angular or linear coordinates for a shapefile

[Dan Homerick]

Hello List,

This probably something of a naive question -- please don't hesitate to
point out what "should be obvious."

I'm creating polygon-filled shapefiles using data extracted from a geotif.
To do this, I'm using the OGRLinearRing::SetPoints() method and then adding
the ring(s) to a polygon.

My question is, what coordinate system should I be setting the points with?
I want the resulting shapefile to still be georeferenced. The way I see it,
I have 3 options, one of which is clearly wrong:

1. Pixel/Line coordinates from the image. (wrong)
2. Linear geo coords, resulting from GDALApplyGeoTransform.
3. Angular geo coords, resulting from something like:

/**********************************************************/
OGRSpatialReference* m_TargetSRS = m_SourceSRS.CloneGeogCS();

m_LinearCoordToAngCoord = OGRCreateCoordinateTransformation(
                                              &m_SourceSRS,
                                              m_TargetSRS );

m_LinearCoordToAngCoord->Transform(...)
/**********************************************************/
where m_SourceSRS is set from the GeoTiff.

Will my shapefiles be properly georeferenced if I use the second method (and
a .prj file is used)?

Will the be properly georeferenced if I use the third (without a .prj file)?

Also, what's the correct names for the "linear geo coords" and "angular geo
coords"?

Thanks!
- Dan
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