[Proj] Re: Local cartesian to UTM using PROJ.4
Frode Tennebø
frode at tennebo.com
Tue May 15 18:30:41 EDT 2007
Greg Troxel <gdt <at> ir.bbn.com> writes:
> Frode Tennebø <frode <at> tennebo.com> writes:
>
> > I'm trying to perform a transformation of a position in a local
> > carteisan system, grid north in meters (XYZ) relative to a UTM/WGS84
> > (ENA) center with the result in UTM/WGS84. I have tried Geotrans
> > (Local cartesian -> UTM, WGE/ WGS84), but have discovered some
> > discrepancies. I would like to use PROJ.4 to verify one or the other.
> > How can this be done in PROJ.4?
>
> I had a similar problem, I think. I defined a local system relative to
> Massachusetts state plane, putting (40,30) in my grid at some SPC
> coordinates. Then I had a rotation - my Y axis was more or less north,
> but not really. (The point was to have a natural coordinate system in a
> parking lot.)
>
> I tried to do this in proj by using the oblique mercator projection, but
> never succeeded. I ended up hand-writing the code, since it was just a
> rotation and translation from the state plane system.
I'm not familiar with the US state plane, but from your description this is
more like the trivial example below.
> Rereading your question: are your X and Y axes along the ellipsoid, or
> is this a translation of an ECEF system? I think it would be helpful
> for you to be far more precise about what you are doing.
I had hoped I was quite precise. :) When I said local cartesian, I meant that
in the strictes sense. I have an origin in UTM (ENA) and a position vector
relative to that origin in meters (XYZ) where Y is grid north (INS delivered -
I just got a bit uncertain if the INS actually delivers true north, I'll have
to re-check that, but for the sake of this argument it's grid north). I assume
by "along the ellipsoid" you mean along the projected north, hence grid north?
So, for a trivial example: Origin is UTM/WGS84 (500000, 6000000, 10) position
vector is (1000, 2000, 100) (1000 meters east, 2000 north and 100 up) ->
UTM/WGS84 (501000, 6002000, 110). Not factoring in scaling.
It's the reverse of the "what's the distance from A to B?" problem so I was
hoping that PROJ had some mechanism for this...?
Regards,
-Frode
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