Footleg

When I first figured out how to draw projected elevations my (somewhat erroneous) assumption was that I could use extended elevation drawings to create projected elevations in almost any direction.

What I found was, yes, of course you can, but the further the particular piece of passage deviates from perpendicular to the direction of projection, the more the distortion.  So, in all but the straightest of caves you won’t like the result. 

Having said that in one of our current projects I still have a scrap drawing (a few years old) that is identical in the extended elevation and the projected elevation.  It is only a little warped in the projection.  However I cheated.  First I drew the extended elevation, then I copied the file and manually changed the projection in one of them.  So even this is not really a case of the same scrap being used in two projections.

The process I use when drawing projected elevations is (whether booking on paper or going wireless with pda);

1. draw the plan view,
2. use therion to plot the projected elevation centerline on paper,
3. Looking at the plan, (and my paperless pockettopo extended elevation sketch if I have one)
4. draw the elevation over the centerline on paper, conceptualizing it into scraps as I go,
5. scan the drawings and then import them into therion and trace over them.

A bit frustratingly manual compared to the paperless process for plan views, but simple and effective enough.

Bruce

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From: therion-bounces@speleo.sk [mailto:therion-bounces@speleo.sk] On Behalf Of Footleg
Sent: Wednesday, 23 March 2011 11:23 a.m.
To: List for Therion users
Subject: Re: [Therion] How to generate a projected elevation alongaspecificbearing?

Now that I have played with this a bit more, I see that I get an error unless every scrap, map and map export projection declaration using those scraps has exactly the same projection bearing. I had thought it might be possible to generate a projected elevation map along a different bearing from that which the scraps were drawn on, but possibly not? Is it possible to generate projected elevations using extended elevation scraps? I am just trying to explore the options for producing projected elevation output from my source data so I can better understand how to draw up my initial elevation scale sketches on paper before trying to therionise them.