Trimming a draped surface from DMT mesh

Hello all,

I have been using the drape command to create a surface over meshes made from ASCII DEM files exported from QGIS using Florian Frank’s DMT for Grasshopper. Everything works well until I go to trim the draped surface, which causes the surface to badly distort and loose definition. I have searched for a solution to no avail, and have tried various tactic such as moving the surface, scaling the surface, changing the units the model, but nothing seems to help.

Any insight greatly appreciated.


Hello - please post an example surface and the trimming objects . Is the surface very far from the world origin?


Hello Pascal,

Thanks for reply.

Good question, one I may not be equipped to answer. The mesh lands where the grasshopper plugin specifies…

Images attached.

[EDIT] Sorry they’re in the wrong order, but they are annotated accordingly.

Hello - I would set custom meshing for that object in the object properties

use a ‘Maximum distance edge to surface’ of say 1 in this case - does that clean it up at all?


Hi again,

seemingly not, unless I’m doing something wrong.

Can you post the objects in a file or send to with a link back here in your comments?


Sure. Thanks

Hello - setting a custom display mesh for the object does work, but my suggested tolerance was too large, I got the scale wrong from the images - use 0.1 or there-abouts as the ‘Max distance edge to surface’ - you may also want to fine tune that and other settings as outlined here:

Why it goes so wrong after trimming, I am not sure yet. Note you can also ShrinkTrimmedSrfToEdge and it will clean up as well - basically makes it untrimmed again, only smaller.


Gooday Pascal,

Wow. I first tired you 0.1 value which, to my great satisfaction, worked perfectly. Then I ran the ShrinkTrimmedSrfToEdge to see if there was further improvement, but it looked much the same, visually at least. Then I tried the ShrinkTrimmedSrfToEdge on a previous trim that appeared distorted and that too, on its own, worked perfectly, again, at least visually. Unless you think visual inspection inferior to some kind of real analysis, I would just say thank you for your help!