[Therion] Calibration of co-ordinate systems

[Martin Budaj]

Hi,

On Mon, May 17, 2010 at 11:17 PM, Andrew Atkinson <andrew at wotcc.org.uk> wrote:
> import Great_Swallet.3d -surveys use -filter great_swallet -cs EPSG:27700
> -calibrate [0 0 0 299912 99991 0]
> #Should be -calibrate [0 0 0 300000 100000 0]
>
> (goodness knows why the calibrate is not right, the bodge is to align it on
> goodle earth, probably my ignorance)

Which therion version are you using? Recent versions include geodetic
datum shift parameter which should eliminate the 90-m difference.

> cs EPSG:27700 -calibrate [0 0 0 299912 99991 0]
>
> gives error
>
> output coordinate system specification requires single parameter

It is not possible to modify cs using 'calibrate' option.

I guess your problem could be solved by defining custom Proj4
coordinate system. For ST square it should be

+proj=tmerc +lat_0=49 +lon_0=-2 +k=0.9996012717 +x_0=100000
+y_0=-200000 +ellps=airy +datum=OSGB36 +units=m +no_defs

Currently the 'cs' command doesn't accept custom Proj4 specifications
like the one given above (this funcionality will be added as soon as
possible), so the easiest way to add this projection is to modify
thcsdata.tcl and recompile therion.

In thcsdata.tcl just duplicate line 52 (s-merc projection) and replace
's-merc' with e.g. OSGBST and proj4 specification with the
specification given above.

Then use cs OSGBST in your data.

Martin