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Best way to turn a 2D survey plot into a 3D model?

Discussion in 'Using Alibre Design' started by ee_chris, Jan 26, 2020.

  1. ee_chris

    ee_chris New Member

    I've been using Alibre for a long time for designing machine parts and assemblies, but I'm trying something new (to me) and would appreciate some guidance.

    I have a 2D drawing of a building site and an existing structure, along with elevations for many points in the drawing. I would like to model the ground with curved surfaces through those reference points and others as required to represent the ground contours. What are some possible ways I could do this in Alibre?
  2. Lew_Merrick

    Lew_Merrick Alibre Super User

    Hi Chris (?) -- I believe that you are talking about Lofting a Contour Map into a basis from which you can work. This is rarely either "simple" oe "accurate." It is a major hassle unless the Contour Map is available as an AutoCAD DWG file. Then it is "merely" a case of (say) importing given elevation contours and completing them to "closed shapes" at different "elevation values" and, when you have completed that (fairly major) effort turning the resulting "set" into a Loft. Otherwise you will have to "digitize" each of the elevation contours into a set of Points through which tou can generate the "closed shapes" required by each "elevation value."

    The best "practice effort" to get ready for this is (in my experience) to create a set of "Circles" at differing "elevations" (not all of them being concentric) and "Lofting" them. -- Lew
  3. idslk

    idslk Alibre Super User

    can you post the raw data? I'm not sure how it should look like and how the data are...
  4. HaroldL

    HaroldL Alibre Super User

    This has been asked before. Check out this post to see if it helps.
  5. ee_chris

    ee_chris New Member

    I have a dwg with layers including the property perimeter and building footprint. I would prefer not to post this. I've successfully copied and pasted entities into sketches in the existing building model.
    HaroldL - Thanks, that thread was very useful. I'm experimenting with the process used and will report back when I've made some progress.

    Thanks for the help! :)
  6. ee_chris

    ee_chris New Member

    Here is an update:

    TL;DR: I got it to work, but there was a steep learning curve and it was a ton of work. I managed to get a fairly accurate surface with the desired elevation lines, but I spent a ton of time fixing errors with the loft tool that I didn't understand through trial-and-error.

    I took a large 2D plot of my property, and located and marked all the elevations I measured with an automatic level, and this was quite a few. Many were along lines parallel to the house sides or property line. Then I hand-sketched elevation contour lines over the whole property in one-foot increments, interpolating using the elevations I shot.

    I started off trying to piece together multiple small lofts using sketches in planes aligned with local features. Noob error. Although adjacent "chunks" shared the same profile where they joined, the loft surfaces often kicked up or down, and I didn't have any luck smoothing them out with other tools. I fell back to making a set of 12 non-intersecting sketches extending well beyond the footprint of the property that were roughly parallel. Each sketch had lines for the bottom and sides, and the tops were a single spline curve. This gave a decent result. There are some local inaccuracies, but with a couple of minor added solids it is close enough for my purpose, which is visualizing possible additions.

    After drawing the planes on my hard-copy plot, the positions and elevations where contour lines crossed were transferred to dimension spline reference points. This was incredibly tedious, and I lost a lot of time learning that Alibre really didn't like doing lofts when the profiles in the sketches were composed of multiple splines or lines. Sketches entered that way (like when I extended the cross-sections to the sides after-the-fact) were eventually corrected by changing the splines/lines to reference curves and connecting all the points with a new single spline.

    In addition to finding and fixing the many sketch issues, I also had to tweak hidden parts of the sketch curves inside the house where there were relatively quick changes in elevation. These made the loft algorithm blow up, and I can't tell you how may times I attempted to generate the big loft, sometimes doing combinations and permutations with the sketches to determine which were causing non-helpful error messages (skin bad UV directions, self-intersecting, cusping...).

    Once I had a working loft I trimmed it to the property limits and cut out the house footprint. I got the contour lines by making two instances of the big loft. Each has a horizontal "through all" extrude cut using rectangles to remove slices that are "even" or "odd" 1-foot increments in elevation. There are some extraneous lines where Alibre-generated surfaces meet, but the elevation lines are easy to distinguish with the slices put back together.

    So, I managed to bumble my way to a usable model, but it wasn't much fun. I don't have personal experience with any other tools more oriented towards organic shapes, but I expect there has got to be a better way to get a similar result.

    Eddy So, AlexB and NateLiqGrav like this.
  7. Wade Waterman

    Wade Waterman Member


    This seemed like a lot of work for sure. It looks good though! I wonder what program surveyors would use to get topographical maps? And I wonder if that file would be something that a regular CAD package could import? What if you wanted to machine that surface? More questions! Haha!

  8. HaroldL

    HaroldL Alibre Super User

    Likely they are using AutoCAD Civil 3D.

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