fixed points in survex

[Lev Bishop]

On Thu, 6 Feb 2003, Mark Shinwell wrote:

> 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. 

Interesting. Please do send more details.

> 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>.

geo handles full TRS transformations (although the lists of
transformations that come with it only use a subset of this capability,
only giving values for the 3 molodensky parameters, rather than all 7
helmert parameters, but the lists can easily be edited) and it can do 
ECEF <-> lat-long <-> Gauss-Kruger grid transformations. Gauss-Kruger is
another name for the Transverse Mercator projection.  
In particular UTM and the Austrian national grid are both Gauss-Kruger
grids. There are many many other grid projections, however, that geo can't
deal with, such as the lambert conformal conic used in france and a few us
states, the double-projection used in switzerland, and various other
projections, including some that get used on maps from "unusual"  sources,
which might be all thats available for some remote areas (eg, charts for
aviation navigation where great circles are straight lines, or charts for
nautical navigation where rhumbs (lines of constant compass bearing) are
straight lines, etc).

> 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.

Haven't looked at GMT, but there's PROJ http://www.remotesensing.org/proj/ 
which is sort of open-source (MIT style license) and seems capable of 
about 30 projections, also TRS transformations and maybe more - I haven't 
played with it just looked at the web site.

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

Thanks.

Lev