[GRASSLIST:1466] Re: Converting surveyor's data

Roderick A. Anderson raanders at tincan.org
Thu Feb 15 14:47:50 EST 2001

This is a forward of my reply. Was having some mail problems so not sure
if this ever made it out.


On Mon, 12 Feb 2001, Roderick A. Anderson wrote:

> On Sat, 10 Feb 2001, Rich Shepard wrote:
> > On Sat, 10 Feb 2001, Eric G . Miller wrote:
> > 
> > > However, if you can translate everything to points in space (rather than
> > > bearing/azimuth) than I think maybe v.transform would be sufficient.
> > 
> > > 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,
> > 
> >   These two sentences frame the problem exactly: translating a distance and
> > direction from a known georeferenced point to another georeferenced point.
> > Then taking the distance/bearing to the next point and georeferencing that.
> > 
> >   Sure, once all the nodes are georeferenced the rest is easy. But, it's the
> > georeferencing step to which I referred. I infer from your answer that no
> > one on the list has looked into this. Guess it's research time for ol' Rich
> > in the Land of Geodesy.
> Let me see if I understand this.  You have some coordinates based on a
> local coordinate system that you need tranformed into geo-whatever
> coordinates.
> Do you know the actual geocoordinates for two or more of the points of
> interest (Section, quarter section corner)?  Something the surveyors tied
> to?  If not, you could guesstimate from a map.  Depending on how accurate
> you need them to be you could apply some surveying adjustment rule - from
> compass to least squares.  It also depends on how precise and accurate the
> survey was that generated the coordinates was.  The simpler method would
> be to get the surveyor to rerun the coordinates using a starting
> georeferenced coordinate and going to (closing on) another georeferenced
> coordinate.  After adjusting the traverse you should have a resonably
> accurate set of usable coordinates.
> Otherwise if you only have the local coordinates it looks like a
> rubber-banding of the data would work for the most part - what I see a
> least squares adjustment being able to do.
> This also assumes you need to match this data to other georeferenced data
> because I think GRASS supports local coordinate systems.
> Getting close?
> Rod

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