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A Geological Exercise In Splines, Polylines & Extrusions
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* May 03, 2019, 03:02:26 PM
Assuming I have managed to attach the drawing, which took a lot of finding as TC seems to hide them very well.....

 For the non-geologists, this odd-looking effort is a diagram of an anticline (an upwards fold in the rocks) with the nearer "limb" fractured and displaced by a fault , then the whole structure partially lowered by erosion. The fault-plane is the ski-jump-like surface across the sectioned part.

These structures arise from tectonic forces compressing the continent laterally, crumpling the originally-flat rocks rather like pushing a rug against a wall. As the force continues against increasing resistance the fold's trailing limb breaks into fault-blocks that become pushed up their fault-planes. 

It is in grey scales because I intend it to illustrate an article I am preparing for a caving-club magazine, explaining these geological features. (Some cave passages are developed along fault-planes.) The magazine has full-colour covers but grey-scale photographs inside.

As a TurboCAD exercise, I experimented with assorted methods for free-hand drawing the shapes flat then extruding them to form the strata. I had also to work out how to make them look solid: one refused to extrude as a solid and I had to start again from the original 2D drawing.

Originally I had used hatchures as these give better contrasts, but they don't seem to like being extruded. Or if they do, I couldn't see how to make them. The diagram doesn't stand too much enlarging due to accumulated errors in a lot of copying and re-drawing, but these won't be noticeable in magazine-page size. I had hoped to copy each spline once so it would form the next stratum's border but couldn't quite make it work.

In order to process each piece of stratum I drew the outline in place but then moved its entities down from the main drawing, into clear space where I could chivvy everything into Joining where I'd not succeeded in using the Vertex snap; then fill the shape. My main method with such a problem is to extend the lines to cross then trim them back. I've not worked out what limits the Meet 2 Lines tool has, but I've never had much luck with it.

The fault-plane is just an extruded, thick spline line.
To break each stratum which originally draped across the whole anticline, I made a copy used the fault spline as the trim line relevant to each part, then linked the stratum borders (the "bedding-planes" in geology terms) with a simple, straight line.

I was also plagued with "orphan" scraps of lines, all having to be rooted out; from the many attempts to make it all work.  Sometimes the splines wanted to break up into dozens of individual lines until I had a vague idea where I might have been going wrong. Also, TC appeared to want to keep putting everything on individual work-planes.   

I've probably gone as far as I need and indeed can with the artwork, except for one thing, and would be very grateful if someone could tell me the secret. I would like to annotate it but can't see how to make the text-boxes appear on the rendering. They show in wire-frame, but that's not much use!

There is a second type of geological fault relevant to the article, but if anything it may be harder to draw reasonably realistically.


On TC Deluxe 19: hobby use.

* May 03, 2019, 06:23:59 PM
That's impressive, Nigel. I've always been interested in geology, but I'm too claustrophobic for speleology.

You wrote, "I've probably gone as far as I need and indeed can with the artwork, except for one thing, and would be very grateful if someone could tell me the secret. I would like to annotate it but can't see how to make the text-boxes appear on the rendering." This requires that you make the text visible when rendering but not the Lines and Polylines in the drawing. I apologize in advance if the following instructions are either too detailed or not detailed enough...

1. Right click in the Design Director and select "New Layer." Call it "Lines & Polylines," perhaps. Make this Layer invisible by clicking in the box beneath the "eyeball" icon beside the name of the new Layer. This will be the new home of these entities.

2. Press Ctrl+T to open the "Select by Entity Type" list; scroll down and click on "Line"; click on OK. The list will close and all the Lines in the drawing will be selected. While they are still selected, move the cursor to the Design director and click in the box beneath the check mark beside the name of the new Layer. Repeat this process to move all "Polylines" to this invisible Layer.

3. Right-click on the icon you use when rendering to open the "Camera Properties" dialog and enable "Nonrenderable objects." (This option is found on the right-hand side of the dialog page.)

Henry H


* May 04, 2019, 05:45:42 AM
Nicely done Nigel.  Though I know very little about Geology.

Your method of trimming back lines is fine, I do that myself sometimes.  Meet 2 lines can seem a bit odd sometimes.  I don't know if v19 Deluxe can use meet2lines on a spline (pro can), but I'd say, don't.  Using meet2ines can alter the curvature of a spline.  Its not a bug, it is just the way splines work.  Trimming back is better for splines in my opinion.


* May 06, 2019, 01:29:53 PM
That's funny - I thought I'd already posted a reply.

Never mind.... Thank you Andy and Henry.

I copied the original (the usual precaution), coloured that and followed those instructions, which I'd printed off to be easier to use.

I wasn't sure anything was actually happening until the text appeared, but it all worked!

By way of relief a second figure, a straight 2D cross-section with simplified geology, to explain a few terms, was almost easy.


On TC Deluxe 19: hobby use.