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Mbuck

DTM ignores breakline

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I understand that VW Landmark does not important feature, which in many DTM packages is referred to as breaklines. Am I therefore correct in assuming that the ?Pad site modifier? is VW's equivalent. If this assumption is correct, then why in many cases am I seeing that such closed polygon site modifiers constraints are being ignored i.e. triangulation continues to cross this bounding constraint. Recently, for example I have a large site approx 9,000 data points but in the centre of the site there exists an old quarry (a deep hole 200 m in depth), which is obviously not developable land; and as such has no point data within that area. Although I have put a pad modifier around that area in an attempt to excise that portion of the site; when I generate a proposed contour the pad modifier boundary is largely being ignored, i.e. the DTM triangulation continues to cross this pad boundary. What condition(s) trigger this? Or is it a bug? If so would it not be more sensible to have another but more robust site modifier/constraint called a breakline which could achieve this end.

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I assume that you mean a fence modifier that is coincident with the pad modifier. This I have tried on many previous occasions but the method always proves unsuccessful. Today, once again, as per your advice, I tried it with this much larger DTM and once again, as per my previous experience, it was unsuccessful -VW DTM algorithm(s) seems to get confuse and VW simply hangs requiring a restart. I suspect that the DTM module is trying to force a batter to be calculated between the fence and pad and because these entities are coincident it cannot calculate the transition; hence the need for a true breakline entity for future versions of VW. If you think this is not the case please let me know a possible alternative solution. Note that offsetting the modifiers will produce a batter between them, which in this case is not intended as one is in effect, trying to create an internal shear cliff face.

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Not exactly coincident -- it should be spaced out slightly (any small amount) from the pad modifier. Our DTM will not handle perfectly vertical faces.

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