[Therion] Add Coordinate data back at last level of Survey Hierarchy?

Wookey wookey at wookware.org
Wed Nov 14 23:59:44 CET 2018

On 2018-11-14 20:36 +0000, Olly Betts via Therion wrote:
> On Wed, Nov 14, 2018 at 07:07:50PM +0000, Andrew Atkinson via Therion wrote:
> > I've not had time to play with this, since Alistair showed me the problem
> > on the weekend. The bit that I cannot get my head round is when 3d are
> > imported with a coordinate system, if a th centreline then connects 2 parts
> > of the survey from the 3d or an entrance coordinate is specified for the
> > 3d, how does this change, or can it change the coordinates of the data from
> > the 3d as the stations from this already has coordinates with little
> > information about the connections  [I hope that makes sense]
> Survex .3d files record the coordinate system the data is in, if one was
> specified.  This was added in Survex 1.2.14 (released 2014-07-05).

Right, and that is metadata saying, effectively, 'the numbers in this
file should be considered to be in a co-ordinate system starting at
X,Y on the planet, oriented this way'.

> But looking at the therion source code, it appears therion never makes
> use of this information.  I suspect therion just hasn't been updated for
> Survex gaining coordinate system support.
> You can specify the coordinate system as an option to therion's import
> command, so for now I guess that's what you have to do.

Right, but (if I understand this correctly), that option does not
change the numbers in the file. They must be valid for the cordinate
system given in the import command. This info effectively says where
the origin for the co-ordinates in the file are to be interpreted-as
(and stuff about axis angles).

So let's say that your survex data was processed in 'local' co-ordinates
so it just starts from 0,0 in arbitrary 'nowhere' co-ordinates.

What Alistair wants to do is read that in, but use it with therion
data that is in real-world co-ordinates (UTM30N).

The question is, can that be offset by some arbitrary number on
reading-in so that it appears in the right place in the UTM30
co-ordinate system? Is a rotation needed too?

Adding a rune to the line saying 'this is already in UTM30' will not
have the desired effect, because data in UTM30 doesn't necessarily
start from 0,0, and even if it did, his survey presumably needs to be
at some other co-ord withint that space.

The import -calibrate x y z X Y Z command looks like it should do the
right thing, so long as the axes are aligned, by shifting from x y z
to X Y Z. 

Principal hats:  Linaro, Debian, Wookware, ARM
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