Survex 1.2.14 cs option

[Olly Betts]

On Sat, Jul 05, 2014 at 04:20:58PM +0100, Graham Mullan wrote:
> Good to see this being included in Survex, but there is no mention as to
> what co-ordinate systems are supported. Is it only UTM as in the example in
> the documentation or would OSGB:ST work?

Currently you can specify a UTM zone in WGS84, or provide a custom PROJ4
string.  The example for the latter in the manual is actually wrong -
you need a "custom" in there, like so:

*cs out custom "+proj=tmerc +lat_0=0 +lon_0=13d20 +k=1 +x_0=0 +y_0=-5200000 +ellps=bessel +towgs84=577.326,90.129,463.919,5.137,1.474,5.297,2.4232"

Quite a mouthful, though that's actually an unusually complex example of
a custom string.

I'd like to have got some more named coordinate systems supported, but
I really needed to get a release out for CUCC to test on their Austria
expedition.

The plan is to support the same named coordinate systems as therion
does, rather than reinvent the wheel, but currently those aren't all
documented, and it isn't clear to me from the source code what some of
the undocumented ones actually mean.  I've already sent a patch to at
least add the missing codes to the therion manual, so hopefully they'll
also actually document what they do.

> Obviously there are a vast numbers
> of systems in use worldwide, in Ireland I might find UTM, ITM or IOS, for
> example, so it would be helpful to know which way to go on this.

For an existing survex dataset which is in a coordinate system, the
first step is simply to specify that (both for input and output).
Then aven can export GPX files, and in future do other things which
need to know what the coordinate mean (e.g. loading terrain data).

Cheers,
    Olly