[gdal-dev] Coordinate Transformation issue

Christiaan Janssen cjanssen at iavo-rs.com
Mon Jul 23 07:44:50 PDT 2012


I've been working with the OGR coordinate transformations for some time and
as long as I can remember, when calling the Transform function, no matter
what I'm transforming to or from I always need to convert the unit length
type of the Z component manually. For example, I've created a "from"
Coordinate System that is WGS84 Lat/Long METERS and a "to" Coordinate
System that is NAD83 State Plane North Carolina FEET. When I call the
Transform function, supplying all three components, the X and Y components
are transformed correctly while the Z component is left unchanged. I
realize that no vertical Datum transformation is done, which is fine, but
what's odd is that the Z value is still in the original meters and not in
feet. What I'm curious of is if this is intended result or am I doing
something wrong. The reason I'm asking is that version 1.9.0 started
converting the Z values for me (I noticed the changelog lists a change of
adding vertical unit support which I presume would be why it does this now)
but when I compiled 1.9.1 it seemed to revert back to its old ways of not
changing Z. It's probably an issue on my end but I was hoping someone could
help. If you need any additional information, just let me know. Thanks.

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