I'm sometimes asked for my opinion on re-creating surfaces when either contours or triangles are available in a MicroStation DGN file. I covered the creation of surfaces using contour data in Footsteps #4, so I'll mention a few things in this issue about working with triangle data.
First off, there is a natural impulse to import the triangles as breaklines. This is fine if the surface is small; however if the surface is large then this method could result in a huge DTM with a lot of duplicate data.
Here are some of my thoughts:
First ... I hate working with triangles as a source of 3D data. But sometimes it's all there is so I deal with the pain of the unwieldy surface size. Now I'm going to talk in bullet-speak:
- If there is a lot of data, sometimes it's better to just keep the DTM in separate manageable pieces if you can't get the overall surface size down. There isn't an insurmountable problem with the separate existing surfaces. It's a bit more to keep track of, but no deal breakers.
- Triangle data has a lot of replication. Every triangle leg is doubled ... but it doesn't double the fun. Every interior vertex point is multiplied by anywhere from 3 to a dozen depending on the triangulation. This equals lots of duplicate lines, and boatloads of duplicate points. Yikes!!!
- If you ever hear that "someone did edits to the model". You have to start asking, "What sort of editing did someone do?" If they used the Change Triangle Edge, that hurts. Who knows where those were done? You would have to view the triangles as they are, convert all of those breaklines to random points (easy) and then re-triangulate. Then view those triangles on top of the original triangles and scan for any triangle legs that are different. Those would be the edited ones. If there are none, then that's good. I personally have found it rare that anyone goes into a massive surface and starts flipping triangle faces.
- If you have a surface that was recreated by importing the triangle legs as breaklines and there aren't any triangle edge flips, then convert all of those triangle-leg breaklines to random points. When you triangulate the surface all of the duplicate random points will be purged automatically.
- Compress the surface after that and viola ... leaner and meaner. You have to get the duplicate breaklines and octo-duplicated randoms out of the surface to reduce the size.
- You might have to create the model in pieces if there is a lot of data. Just take one area at a time and mop it up. Then once you have some clean pieces, you can start considering combining them and end up with a more manageable single surface of a reasonable size.
- Of course the survey breaklines, roadway crown, shoulders and what not, are gold. If there are any real breaklines from survey or aerial mapping data, don't mess with those.
- Ask for more memory in your computer ; ) ... and punch up the virtual memory!
- Subcontract this surface cleanup work to an InRoads expert who loves working on surfaces and will return a clean, mean, lean DTM. ; )
- Anyone working on surfaces made up of either contour data or triangles needs to ask for a raise ... that stuff is tough to work with.
- The 'Best Practice' is not to build surfaces like this.
- Oh, and think about viewing all of the surface data in a MicroStation file and running the Delete Dup (Data Cleanup) tool on it. And then re-importing the cleaner data back into the surface.
That's all I have for now : )
A Message from the Zen Dude
Hello One and All!
I'm going to make this short and sweet, because I have a lot to do these days. : )
. . . It's 2016, a new year! We see it as a continued opportunity to do what we can to make you more successful at what you are expected to do. (I outlined our plans in my last ZI #90 letter.)
My parting thoughts to you in this letter are very sincere, and not meant to be sappy or cliché - Our goal is to help you become successful by turning you and / or your users into competent, productive Engineers and Surveyors who understand their roles and can do their jobs more efficiently and technically correct with their software tools.
Until next time, and as always, contact me as needed. I'm here to support you.
- Mark aka "The Zen Dude"