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DTM with Multiple Modifiers? Help!


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Hello ?

I?m attempting to complete a residential design that is situated on a fairly steep lot with a lot of varying slopes, rock outcroppings and other topographic features. The design requires several slabs at varying heights, plus a sloping driveway. Some of the ?slabs? are discontinuous, so there?s no way to combine them all into one 3D solid to use as a modifier (one part of the site has to be excavated for landscaping, there?s a separate pad for the HVAC condensers at a different elevation, etc.) I?ve successfully generated a DTM from the DXF file my surveyor gave me, and I?ve been able to modify it, but only with mixed results.

The essential problem that I have is that the modifiers seem to cut into the hillside only around the perimeter of modifier, but the interior volume that should have been cut away is still mostly there. An example would be if I?d setup a square slab as a modifier and updated the DTM, I?d be left with something that looked (roughly) like a square shaped trench dug into the DTM (not a whole cube carved into the land). This seems particularly prone to happen with the roadway object I?m using for the driveway (I get little mountain peaks at roughly the height of the original DTM jumping out of the middle of the roadway). Other times I'll get what seems to be a perfectly normal cut, except there'll be one oddball point that peaks up.

The whole process is particularly maddening because it takes quite a while to update the DTM, then the only way to really see what?s going on accurately is to go render it with shadows? Probably time for a faster computer here.

Anyway, I?ve been experimenting a lot, and at this point I?m not sure if the things I?m trying are just superstitious on my part, but I could REALLY use some answers?

When creating multiple modifiers for a single DTM, do you draw one ?fence? line around the whole thing? Does anyone have any experience/tips when using multiple modifiers?

Exactly what class should the modifier objects (the 3d Polys) be? Exactly what class should the fence (the polyline boundary) be? Exactly what class should the DTM itself be?

Is there some ordering dependency for the DTM, the modifiers and the fence? Does the fence need to be ?in front of? the modifiers, and the modifiers ?in front of? the DTM?

When making changes, is it better to update the existing ?Proposed DTM? or to simply re-create the proposed DTM from the original site DTM?

For the modifiers and the fence line, are there any requirements in terms of fills? At one point I?d thought I?d got things working right when I made the fence poly-line solid, but now still no luck?

I know some of this is explicit in the manual, but I?ve had such a frustrating mixture of partial success and complete failure here? A complete understanding of what I?m doing wrong would be a huge help? I?m using VectorWorks 9.5.1 on a PC.

Thanks in advance,

Jim Scheller

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  • Vectorworks, Inc Employee

Jim, I'll try and address your questions below as best I can:

"...The essential problem that I have is that the modifiers seem to cut into the hillside only around the perimeter of modifier, but the interior volume that should have been cut away is still mostly there..."

One possibility here is that you're still viewing the Existing DTM which is blocking the "cut" areas of the site. Select the Existing DTM symbol instance and set it to an invisible class.

"...An example would be if I?d setup a square slab as a modifier and updated the DTM, I?d be left with something that looked (roughly) like a square shaped trench dug into the DTM (not a whole cube carved into the land). This seems particularly prone to happen with the roadway object I?m using for the driveway (I get little mountain peaks at roughly the height of the original DTM jumping out of the middle of the roadway)..."

This occurs when you don't have a fence modifier surrounding your pad modifiers. Think of a fence as a "limit of construction". The fence causes the DTM calculator to ignore "original" site data that it surrounds. When creating multiple modifiers for a single DTM, do you draw one ?fence? line around the whole thing?

This is one way. You can also draw a fence around each individual pad. Just remember that the DTM will try and "fit" the site to the pad beginning at the limits established by the fence.

Exactly what class should the modifier objects (the 3d Polys) be? Exactly what class should the fence (the polyline boundary) be?

Pads should 3D polys of the class "Site-DTM-Modifier". Fences should be 2D polys of the -same- class.

Exactly what class should the DTM itself be?

This doesn't matter.

Is there some ordering dependency for the DTM, the modifiers and the fence? Does the fence need to be ?in front of? the modifiers, and the modifiers ?in front of? the DTM?

No.

When making changes, is it better to update the existing ?Proposed DTM? or to simply re-create the proposed DTM from the original site DTM?

Update.

For the modifiers and the fence line, are there any requirements in terms of fills?

No preferences. Should operate on class only.

Hope this helps. Let me know what results you get.

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Hi Robert -

Thanks for the reply to my numerous questions... I've tried to go back and rework things again, and I'm still getting oddball results.

My original DTM is on a separate layer and not visible in any of the other layers I'm using to check results of the DTM modification.

I verified all the pads and fences are SITE-DTM-Modifier class, and I made sure the fence showed as "Polygon" in the Shapes tab and the pads show as "3D Polygon". All of the primitives are closed (can't tell anything from the roadway, but I assume this is okay.) I tried removing the roadway and updating, but got the same problems on the remaining pads on update.

When I modify the DTM I still see the oddball peaks showing through. If I move the pads around, I get different results so I know I'm updating the right DTM.

I tried completely redrawing the fence around the pads and it also made no difference.

I'm stumped... do you have any other things I might try?

Many thanks,

Jim

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Just a quick follow up... Robert took a look at my drawing and simplified the geometry of the pad modifiers. This has corrected my problem.

I had constructed the pads by adding together various 2D primitives (including circles) and then converting the combined surface into a 3D polygon... The circles contributed a large number of vertices to the resulting pad, and this seems to have been what was tripping up the modification of the DTM... Now I've got perfectly flat planes, exactly where I want them in my DTM... Bring on the bulldozers!

Thanks, Robert!

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