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Slope analysis

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I have finally purchased VW 9 and while I am impressed by the intent of the new DTM, I am somewhat confused as well.

Tried to use the slope analysis facility, but don't seem to get any appropriate results. According to the documentation, there should be a colour change for every increment of the slope, but the dialog (on the Mac) does not refer to increments. Furthermore, the calculations seem to give erroneous results: the site in question has grades between 1:90 and 1:8 and I only get one colour (blue), spread rather randomly and with little resemblance to any slope variations. I have tried various values for the slope (from 1 dgrees to 8 degrees) and the results look too similar to be true - and in fact are totally wrong, unless I don't at all understand how this is supposed to work.

In fact, I do get some red and pink, but those are in an area where the entire DTM is calculated incorrectly, with DTM contours crossing happily the 3D polygons of the terrain data. Partly this is perhaps caused by the source data, but still rather disturbing: if the DTM interprets the terrain entirely wrong here, does it do the same elsewhere as well?

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  • Vectorworks, Inc Employee

Petri, I've done some thinking about your post, and re-read the manual description (which was terse), and felt like some clarification was in order. First, the slope analysis is based strictly on the polygons created directly from your input data. (This is also known as the TIN, or triangulated irregular network [of polys], but you probably already knew that.) So the "granularity" of the slope data is limited to the actual data provided to create the DTM. This makes sense, as it would be possible to use interpolation to "fool" the slope analysis. So each 3D poly in the TIN has its slope determined and the resulting slope is colored according to the scale you specify in the dialog. (i.e., change color every 2 degrees, every 5 degrees, etc.) Are you not obtaining this result? If you think not, please send me the MCD file and I'll take a look at it.

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  • 2 months later...

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