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michaelk

DTM for beginners

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I'm hoping someone can set me in the right direction.

I'm trying my first "real" DTM (doing it the real way and not just using the Loft Tool).

I have a dwg of a site plan. The contour lines are in 3D, and each contour line is a symbol. Each symbol is made up of many, many 3D polys. It appears that each poly is a ca. 15" line - or a 3D poly w/ only 2 vertices.

Do I have to get the 3D polys "out" of the symbols? Or trace over them?

Any suggestions?

Thanks!

michaelk

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I personally find it easier to trace over, but others might have different opinions. Do the following: 1) On a new clean design layer, trace over each contour, using the POLYLINE tool, starting with the LOWEST and working to the HIGHEST elevation. 2) Select all of the 2d Polylines and run the menu command: MODIFY/CONVERT?CONVERT TO POLYGONS. 3) Select all the Polygons and run the menu command: AEC/SURVEY INPUT/ 2d POLY'S to 3d CONTOURS. During this process you will be given some choices, like the elevation interval between contours, etc. then, each of your 2d polygons will highlight, one at a time, starting with the first created, and then the next, etc, each time you click Next. When all of them have been converted you will be asked if you want to save the originals. If you do, put them on another layer (you may want them later...) 4) Select all the new 3d Contours (which are actually 3d Poly's) and change their fill to None (in the attributes palette). 5) With them still selected run the menu command:AEC/Terrain/Create Site Model. There are lots of choices here, all of which can be modified after creation, so don;t worry too much about every single one.

Hope that helps...

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Thanks, guys. I was afraid of that...

Could I select a symbol (made of 3D polys), then convert a copy to lines, then compose the lines to get polygons?

There are hundreds of lines, and I'm hoping to find a way that doesn't involve tracing all of them.

Thanks

michaelk

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Mike

That looks very interesting. It says v13 (2008). Do you know if it will run on 2009?

Thanks!

michaelk

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Back to the original question:

Is there a trick I could have done while importing the dwg to not have everything come into VW as symbols?

And, if not, is there a reason that polygons from Convert Copy to Lines then Compose would not produce satisfactory polygons to create a DTM? (If there were little breaks in the polygons would that cause problems?)

Thanks for all your help. I'm thrashing around a little trying to get the whole DTM concept into my limited brain space all at once.

michaelk

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have you had a look at my blogs and podcasts, there might be something of use there.

Jonathan

I'll go back and look at your blogs and podcasts. I'm a big fan. If the joy of figuring it out wears off I'll be buying another one of your books.

Thanks

michaelk

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Describe your base data - Is it AC 2009? Can you have your data supplier resend the data in a earlier AC version?

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Thom

Part of my problem is just my ignorance and inexperience with DTMs. I got a dwg that I assume is AC 07, 08 or 09. But I have no way of knowing.

The survey is several years old. It has a complex array of classes, groups, and symbols that make it hard to know what is what. But the contour lines are easy to figure out.

(and for some reason most of the drawing is 6 MILLION feet right of the origin and 2 MILLION feet above. The remainder of the drawing is 6 MILLION feet left and 2 MILLION feet below!)

michaelk

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Michael, I would be happy to do a phone conference and help you get on the right track. Let me know if this is of any interest to you. Peter

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Michael try extracting only what you need from the survey file using Custom Selection and paste it into a new file so it is centred around the origin.

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Mike

That's my plan. I want to plant some reference points first in case I need to move something else into my new document.

Thanks everyone

michaelk

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michaelk-

If you need to find out the version of the DWG file, open the DWG file with TextEdit (or another text editor).

The first 6 characters you see will tell you the version:

"AC1002" = DWG from Rel. 2.5

"AC1003" = DWG from Rel. 2.6

"AC1004" = DWG from Rel.9

"AC1006" = DWG from Rel.10

"AC1009" = DWG from Rel.11/12

"AC1012" = DWG from Rel.13

"AC1014" = DWG from Rel.14

"AC1015" = DWG from ACAD 2000/2000i/2002

"AC1018" = DWG from ACAD 2004/2005/2006

"AC1021" = DWG from ACAD 2007/2008/2009

"AC1024" = DWG from ACAD 2010

HTH,

Tim

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I personally find it easier to trace over, but others might have different opinions. Do the following: 1) On a new clean design layer, trace over each contour, using the POLYLINE tool, starting with the LOWEST and working to the HIGHEST elevation. 2) Select all of the 2d Polylines and run the menu command: MODIFY/CONVERT?CONVERT TO POLYGONS. 3) Select all the Polygons and run the menu command: AEC/SURVEY INPUT/ 2d POLY'S to 3d CONTOURS. During this process you will be given some choices, like the elevation interval between contours, etc. then, each of your 2d polygons will highlight, one at a time, starting with the first created, and then the next, etc, each time you click Next. When all of them have been converted you will be asked if you want to save the originals. If you do, put them on another layer (you may want them later...) 4) Select all the new 3d Contours (which are actually 3d Poly's) and change their fill to None (in the attributes palette). 5) With them still selected run the menu command:AEC/Terrain/Create Site Model. There are lots of choices here, all of which can be modified after creation, so don;t worry too much about every single one.

Hope that helps...

I'll say that I generally disagree with this method, since polyline to polygon conversion creates huge vertex counts, and I've never had any luck with the 2d polys to 3d polys (contours) saving me any time. I'd further avoid any conversion attempt of dwg imported geometry for the same "control my vertex count" reason, as well as the likelihood that there are overlaps and other faults that could be tough to troubleshoot.

Instead, I trace my survey info with 2d polygons so that I can control my vertex count. Only I know where I need tight spacing, or not. Vertex reduction has always been very important for DTM/Site Models. I generally throw in some 3d loci as well where I have point elevations that I need. Next, select all the 2d polygons and convert to 3d polygons, ungroup to get individuals, set fill to none, and then select and enter each z-height in the OIP. Check the look of the 3d poly and loci 'cloud' from an isometric view or two, rotate the view with the flyover tool to make sure nothing is missed or whacky (zero, or 100" high instead of 100', etc.), then run the create Site Model command.

Next, check the look of the Site Model in the format you need. It will likely look great in 2d (w/ 2009), but if you use any 3d format beside extruded contours, you'll likely have some dirt spilling over (or have some dirt washed out from under) your contours. After copying this into a fresh file and sending it to NNA as a bugsubmit, a few tricks to try to massage the result that sometimes work are to add additional (or trace existing) contours and convert them to site modifier "pads" (with a fence), adding some 3d loci, adding some 3d polygons, moving the existing 3d polygons just a smidge (check them in a iso view to make sure they didn't get moved to z=0), etc. Note site modifier "pads" do not need to be enclosed shapes- a line can be used even.

The DTM/Site Model tool has always been an almost great tool- they keep chipping away at the edges, but can't seem to get it to "just work".

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Hi Chad, are you aware of the "Filter 3d Polygons" command? It will lower your vertex count greatly!

I use polylines, in the second mode, because it's easier to match the curves that way (at least for me).

P

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Yes, I just like the ability to choose where and how to reduce the vertex count. I don't delegate well, apparently!

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LOL. Different strokes for different folks: one of the greatest strengths of Vectorworks! P

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I have used the freehand tool to create contour lines. I use a mouse, but it would also work great on a tablet.

If you set the freehand tool to high or very high smoothing but choose no smoothing as opposed to bezier or cubic arc smoothing, the normal polyline created stays a polygon with very few vertices, yet reads smooth in 2D.

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Another way to control vertex count is to duplicate along a path. Path is any contour, 2d, 3d, dwg contour, VW trace or any other source. Dupe object is a 3d locus. Choose how many verticies or spacing in the DAP tool prefs. Assign each dupe group to a new class named as the z value of the contour. If necessary, raise the whole class to appropriate z. Place the contours and loci on separate layers. Create the DTM from the loci, not the contours. Add loci, 3d polys, etc to trouble spots if necessary

-B

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