Generated Mesh ridges make incorrect topo

[R Muller]

The ArchiCAD algorithm to generate meshes is incorrect, and does not work in accordance with the documentation in the user guide. This gives incorrect "dead flat" spots in the terrain instead of correct ridges and valleys.

Ridges are generated that connect mesh points at the same elevation on the same user-defined ridge, rather than connecting only user-defined ridges that are at different elevations. See the enclosed example of a real-world topo with at least a dozen incorrectly generated ridges.

In every case the incorrect ridge line is shorter than the correct ridge line would be. The algorithm needs to change so that points at the same elevation on the same user-defined ridge line will never be connected.

This has been the case in every version of AC since the mesh tool came out.

[Katalin Borszeki]

HI, sorry, but what you are requesting is just currently not possible.
You can add new lines and points to make the mesh take the shape you want , but then a new triangulation will appear and maybe other segments will not be as you imagined. We have added this to a similar wish...best, k

[R Muller]

Katalin, Thank you for looking at this and making a note of it.

I am doing grading designs, including calculations of cut and fill. I find my calculations do not match a civil engineer's calculation for the same grading design, and my guess is this incorrect triangulation is the main reason for the difference. If I am modeling a valley, the volume of my mesh as calculated by ArchiCad is too big because of the incorrectly generated flat areas where each contour makes a "V" at the bottom of the valley. If I am modeling a ridge, my volume is too small because the incorrectly generated flat areas are at the top of the ridge.

I also note that the current AC21 user guide states: "Each generated ridge connects two Mesh points at different heights that are not already connected by a user-defined ridge." This isn't true; the generated ridges frequently (and incorrectly) do connect mesh points at the same height. If the mesh tool actually did what the user guide says, it would be a better tool to use for depiction of real-world topography.

I remember when the mesh tool was first introduced. It changed my life. Before this, I was trying to make topography using roofs. The mesh tool was a wonderful improvement. I use it a lot. It has taken me years of use to define and understand this problem with the tool, and my guess is that it won't be tremendously difficult to fix. I hope you can fix it soon.

[R Muller]

Here'e an update for AC22. ArchiCAD still generates incorrect typos. Here's an example of dead flat spots at the corners of a grading plan. It makes for lumpy topography and site areas that won't drain.

Yellow shaded areas have incorrect topography. Blue lines are user defined topo lines. Red lines are Archicad-defined ridges. Green lines are where ArchiCAD should have triangulated the lines in order to create real-world topography.

[Lingwisyer]

R wrote:
flat areas where each contour makes a "V" at the bottom of the valley. If I am modeling a ridge, my volume is too small because the incorrectly generated flat areas are at the top of the ridge

Should you not have defined valley depths and ridge heights anyway?

R wrote:
Here'e an update for AC22. ArchiCAD still generates incorrect typos. Here's an example of dead flat spots at the corners of a grading plan. It makes for lumpy topography and site areas that won't drain.

Yellow shaded areas have incorrect topography. Blue lines are user defined topo lines. Red lines are Archicad-defined ridges. Green lines are where ArchiCAD should have triangulated the lines in order to create real-world topography.

That was one of the convenient things about Sketchup. Being able to delete the offending line and insert a correction.

Have you tried any of the 3rd party mesh generators? Not sure if they do any better, just curious.



Ling.

[R Muller]

I love the mesh tool. I remember when it was introduced, about 15 years ago, and I no longer had to try to construct sloped sites out of roofs. It made my life much easier.

However, I think the tool is due for a major upgrade. My wish list:

• The choice of pens for user defined vs. generated ridge lines is inconsistent between 2d and 3d.
• I haven't found a way to translate a mesh to IFC that is usable by the recipient to review the grading design.
• There should be a way to automatically generate new contour lines on an existing mesh.
• Polyline tools such as offset and multiply should be available to create new user defined ridges on a mesh.
• We should be able to define different line types and/or colors for specific user-defined ridges so that we can use the mesh itself rather than a separate set of polylines to have a graphically good grading plan.

See my post here BEST WAY TO EXPORT MESH OR 3D TOPO FROM AC22 TO GIS? https://archicad-talk.graphisoft.com/viewtopic.php?f=12&t=62047&p=287766#p287766 regarding translation.

Ling, per your comments, I do sometimes add sloped ridge and valley lines to my meshes, but these are awkward because they cross the contour line ridges, making further modifications to the mesh difficult. ArchiCAD allows crossed user ridge lines, but the results are somewhat unpredictable.

I have not tried any third party mesh generators. Are there any good ones?

[Lingwisyer]

I usually only add the highest and lowest points within a valley / ridge.

I have been using ArchiTerra, but since it is the only one I have used, I cannot say if it is any better or not...



Ling.