[Therion] Projected Elevation Reprojection

[Footleg]

I am just starting to try and draw up my first projected elevations in
Therion (only 5 years into the project!). I have found that you cannot
reproject an elevation from one bearing onto another (Therion only includes
elevation maps containing scraps of the exact same bearing as the export
statement).

e.g. In my thconfig:
    export map -projection [elevation 180] -layout local -o ElevEW.pdf

My scrap type is set to: elevation 180
If I don't declare the projection in my map, then the map is only included
in the export when the bearings match between the export and the scrap.
(180 degrees meaning the elevation is a projection looking due South, so
the drawing represents a slice through the cave from East to West across
the page from left to right.

I am drawing the scrap using an extended elevation sketch from PocketTopo
which is from a passage which trends approximately due West going
downslope. This works OK and the distortion is minimal my elevation comes
out looking pretty much like my scrap drawing.
[image: TherionElev180.png]
But I want to draw my projected elevation sloping down from right to left,
as that matches the plan drawing. If I just change the export to  [elevation
000] then nothing is output (the map only contains scraps with elevation
180, so the map is not included. If I try to force the map to use
-projection [elevation 000] so that it matches the export statement then
Therion throws an error saying there is an incompatible projection in my
map (because the scrap is elevation 180).

Realising that the scrap gets distorted to match the bearing (i.e. I have
drawn an extended elevation sketch, but side the scrap is projected at
180), I tried to set the scrap to 'elevation 000'. Afterall, Therion should
just distort the drawing to align the stations along on the plane of the
projection right? Well sort of. What could be expected to be a simple
reversal of the scrap, actually makes quite a mess of it as you can see in
the elevation [000] rendering:

[image: TherionElev000.png]

This looks like a bug in the distortion code. I think the ceiling and floor
have been swapped (i.e. Therion has rotated the scrap along a horizontal
axis going into the page rather than flipping it left-right. But it has
also bent the ceiling and floor lines into some sort of geological folds as
well.)

Am I missing any tricks here? Do I need to manually try to reproject all my
extended elevation sketches onto the projection I want to draw my scraps
using, and scan them back in as background sketches? Does anyone know of
any tricks to perform the sort of 'horizontal' distortion I need here (i.e.
Only moving the pixels of the sketch in the horizontal dimension, not the
vertical? I need to learn this inside out so I can write the projected
elevations chapter of my tutorial!

Footleg
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