Help with Compass dat files read (and processed) by Survex

[Olly Betts]

On Sun, Oct 12, 2025 at 07:42:28PM +0200, Josep Guarro wrote:
> I see on the DAT file that the shot lengths values from station to
> station are the same ones that in Ariane, for instance shot form
> station 0 to 1 in Ariane (metric) is 15.86m, then on the compass
> exported DAT file I see also that from station 0 to 1 the length is
> 15.86 but I do not know why survex is assuming those lenghts are in
> feet?

It sounds like Ariane's .DAT export is incorrect for metric data.
Here's the documentation for the DAT format:

https://fountainware.com/compass/HTML_Help/Compass_Editor/surveyfileformat.htm

Against length, left, up, down, right this says (my emphasis):

| It specifies [length/distance] in *decimal feet*

So the DAT file should not say 15.86 if the length is 15.86m - instead
it should say 52.034 (or 52.03 or however many decimal places you think
appropriate).

> I'm not used to Compass, is there any way to write down in the compass
> DAT file that the lenghts are in meters rather than feet?

There are two fields which say what the **ORIGINAL** length/distance
measurements are in:

| II.	Length Units: D = Decimal Feet, I = Feet and Inches M = Meters
| III.	Passage Units: Same as length

However the measurements themselves should always be converted to
decimal feet (so the "Length Units" field lets you display the
measurement in its original units, though may be rounding issues for
some values - storing an extra decimal place as I showed above should
reduce that problem significantly).

(My guess is that originally Compass only supported feet, and when
metric support was added Larry chose to leave the distances in metric
so that existing readers of the file could continue to work with new
files.)

Angles are handled similarly - they're always stored in decimal degrees
with fields to say what the original measurements were in.

Cheers,
    Olly