[Therion] Making projected elevations

[Tarquin Wilton-Jones]

Hi Nick,

Thanks for the insight into PocketTopo+Topparser. I am passing it back
to the author of SexyTopo as well.

> By using PocketTopo and then using Andrew Atkinsons Topparser
> [...] you have the option of producing a projected elevation .th2 along with
> a projected xvi which shows all your splays and not just the centreline.


It would be a bit late to switch to PocketTopo ;)

But this is basically how I am doing it with Therion itself, which does
not rely on an external app, and should work no matter what tool you use
to collect your data.

1. Survey whatever I am going to survey, get the .th files for the
centrelines.

2. Link them together. This step means that any projected lines pointing
towards the camera are in their roughly final position (new loops can of
course change that), so there is a lower chance of loop closures messing
up the directions. This step is not needed, but it makes me feel better
knowing that they will not be distorted as much after I draw them, and
declination is catered to, etc.

3. Therion:
source "cavesystem.th" #overall file, not the individual survey file
select surveyname at section.cave #surveyname not mapname
export map -projection [elevation 265] -fmt xvi -output "surveyname
elevation265.xvi"

4. Therion. F2. Create a new th2 file, save as
"surveyname elevation265.th2"

5. Edit - Insert image - select "surveyname elevation265.xvi"

6. Refer to the ee drawings with centreline, which were taken in the
cave. Replicate them using the splays and centreline on the projected
elevation.

I'll see if I can add these various howto notes somewhere useful on the
wiki.

It would be lovely if - in step 3 - we could say "and use the extended
elevation drawings as your basis" to make it export the drawing as well
as the splays in the xvi, with the drawings wrapped around the
centreline. It won't be perfect, but it would make it so much easier to
trace over the parts where it is a good enough match, and just correct
the parts that are too badly warped. But I think I am dreaming here.

Martin's PDFs did a great job of showing why I came to the conclusion
that I will have to do this manually, but imagine Martin's drawings with
centreline and splays as your xvi to get you started, and it would be
much nicer to work with that, rather than just a centreline with splays,
and no passage sketch.

Cheers,

Tarquin