Discussion Forum

Hi Alexandros, After creating an interpolation function "z=myfunction(x,y)", you'll need to use that interpolation function in a parametric surface, and then use that parametric surface to partition a solid domain, say, a cube.

See this blog post, which gives more details and uses an elevation function instead of an interpolation function but otherwise follows the approach I just mentioned: https://www.comsol.com/support/knowledgebase/838/ Best, Jeff

Hi Jeff, thanks for the reply. I had already found the knowledgebase post on this, but it wasn't very helpful. The link to the DEM file is dead, but i did manage to find it and now I am trying to reproduce the whole geometry definition of the model.

Also, it would appear that any format other than DEM is not handled as easily for this purpose. Given that points with coordinates are the easiest format to exchange between various programs, why can't I make a a surface out directly out of the point cloud data? I tried converting the polygon to a surface but I keep failing. I would expect this to be pretty straightforward. Am I missing something?

I have been able to create the parametric surface with an interpolation function for my data. However since the geological domain boundaries are not aligned to N-S and E-W axis i get a surface that is larger than it needs to be. How can I trim this to the boundaries of my geo-data?

Hello Alexandros, I am glad to hear you were able to turn your point cloud data into a parametric surface. You can trim it by using the usual geometry operations such as intersecting it with solids, etc. Before you do that, you may want to consider extending your data out a bit with fictitious values to avoid oscillations at the edges of your data. See this link for a more in depth discussion: https://www.comsol.com/forum/thread/143132/importing-odd-shape-dem-and-xyz-available?last=2017-05-03%2016:33:44 . If you need further assistance, please contact COMSOL support at support@comsol.com . Best regards, Jeff

Hi Jeff, what i don't understand is why is it so difficult to create a surface from XYZ points. I don't understand this. When I try to convert the XYZ file to a surface i get an empty object. Surely there must be a way to do this. Can you please clarify? thanks Alex

I must have misunderstood your earlier post. I had read the first sentence of your last paragraph to mean that you had been successful.

It is a fairly straightforward approach, and it sounds like you are trying to follow it: 1/ create an interpolation function based on your data file, 2/ use that function to define a parametric surface. Since you are reporting that you are getting an empty object, my guess would be that there is something going on with your data or with the way you're calling it. Figuring things out more precisely will require a look into your data and how you're using it in the mph file. If you need further assistance, please contact COMSOL support at support@comsol.com . Best, Jeff

Hi Jeff,

I have been able import the surfaces this time as polygons. The problem now is getting from the polygon to a surface. Converting the polygons to a surface results in an empty object. Why is that and what could be the solution? Or is there another way to do this? Greetings Alex

Hello Alexandros,

Please contact COMSOL support at support@comsol.com for further assistance.

Best,

Jeff