[GRASSLIST:1437] Re: Converting surveyor's data

Eric G . Miller egm2 at jps.net
Sat Feb 10 18:46:59 EST 2001

On Sat, Feb 10, 2001 at 03:11:12PM -0800, Rich Shepard wrote:
>   If the answer to this question is in a man page or other document, please
> point me to it because I did not find the answer when I searched for it.
>   I have data produced by surveyors that I need to get into GRASS. In the
> US, at least, surveyors work in their own, local coordinates rather than in
> georeferenced coordinates. This means that they will find a section corner
> monument in the ground, then run their survey from that point using metes
> and bounds (or, angles and distances). This is how land documents are
> legally described in this country. Even though surveyors now have access to
> real time, kinetic, differential GPS that permits them to survey quickly and
> to 1-2 cm accuracy, many still plot their maps as azimuth and distance from
> a known point.
>   How can I translate these local coordinates to a standard
> projection/coordinate/datum system (e.g., State Plane Coordinates, NAD83)?
> If this is not currently available, is there anyone willing to work with me
> on quickly producing a conversion filter? I have a new project that requires
> this.

I've thought about this before... I don't get data from surveyors so I
don't know the format(s).  However, if you can translate everything to
points in space (rather than bearing/azimuth) than I think maybe
v.transform would be sufficient.  I don't imagine most survey data
is for very large areas, so things like the curvature of the earth can
probably be ignored.

If there's some kind of way to tag the reference points to real world
coordinates from whatever file formats are provided, then I'm sure a
script could be worked up to build a vector line layer.

Eric G. Miller <egm2 at jps.net>

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