fixed points in survex

[Mark Shinwell]

On Thu, Feb 06, 2003 at 03:37:35AM -0500, Lev Bishop wrote:
> First, I think that since survex already accepts cartesian coordinates for
> fixed points, it would be easiest to implement grid projection, geoid
> modelling, TRS/TRF conversion, tectonic modelling, etc - everything
> relating to fixed points - outside of survex itself in some kind of helper
> wrapper application that takes lists of fixed points in some kind of
> tabular format (grid, TRS, TRF, coords, epoch, location ID, etc) and spits
> out something like a fixedpoints.svx file that can be *included into the
> actual survey files.

Indeed, that does sound like a good idea.  This summer, on the Cambridge
expedition to Austria, we're planning to experiment with some fledgling
part-home-built IDGPS technology.  Since we're taking the trouble to do
that (primarily for the purpose of more accurate location of fixed
points, and easy extension of the set of fixed points), I suspect we'll
spend some time thinking about some of the above issues too.  You'll
probably find a nasty Perl script comes out at the end :-)

> This helper app is not strictly required but it would make life
> much easier for the average cave surveyor who has no interest in geodesy.

I think "much" is an understatement!

> Transforming grids should be easy to do and there probably is GPL-ed code
> out there for many, although there are quite a lot of grids in existence.

There's a program called "geo" which handles quite a lot of this stuff,
which we've successfully used in Austria to perform coordinate
transformations.  See
<http://homepage.ntlworld.com/anton.helm/garnix.html>.

There's also GMT <http://gmt.soest.hawaii.edu/> which might be of use
for those involved in map-making, and I note that www.freegis.org
appears to have a comprehensive list of software which might be useful
for performing some of these tasks.

> Phew! Sorry that was so badly organised, but I couldn't face working it 
> into a more logical order. You can go back to ignoring me now.

I take my hat off to you :-)  A very interesting read.

Cheers
Mark
-- 
Mark Shinwell -- http://mrs30.quns.cam.ac.uk/ -- Mark.Shinwell@cl.cam.ac.uk
Theory and Semantics Group, University of Cambridge Computer Laboratory