Displacement not working on this or similar objects

I have a long girder shape that’s curved is meshed with triangles. Not too heavy. I then mapped an image of a girder with the cutouts being alpha channeled. This works nice but I want to give thickness to the alpha channeled map.
I’m trying to displace a mesh using prb material displacement slot. It only breaks the mesh at the seams but no displacement happens other than that.
I looked at a similar thread and Nathan prescribed custom mesh settings, but since this already is a mesh the settings are greyed out.
I tried custom mesh settings in options but that had no effect I guess other than remeshing this entire complex model to get more geometry is there nothing else to try?
Section of a small girder file attached with textures (I hope).

GirderWithAlphaTexture.3dm (3.1 MB)

Displacement doesn’t add thickness, but relief.

The breaking happens because the mesh is not welded on the corners, so these come apart.

Custom mesh settings work for breps, not for extrusions, nor for meshes. You can QuadRemesh, but due to the size of this object you’ll need a lot, and even then you don’t gain much visually.

Below a few steps of remeshing. On the right your original object, then remeshed with 2000 faces, 20.000 faces and 2.000.000 faces.

As you can see, not much is gained here. In Raytraced it will look best, but even then it still isn’t good, here the 2M poly structure. You can also see that the displacement texture isn’t all that great - for instance the rivets are half out, half in.

You can see that for this object you need more geometry than is healthy. And that is for just this tiny bit. You can imagine how heavy the object is going to be in your actual model.

If you want good looking results then in this case I’d suggest you actually model it. Or just be satisfied by using a bump map.

Hi @nathanletwory,

That little truss is just a tiny, tiny part in this 197 meter airship. I didn’t think it was doable but thought I would give it try and ask the experts. The trussing is only a part of the model. I’ve been able to keep the model slim yet light with this meshing and alpha channel mapping. Perhaps one day I’ll get hardware that could handle an actual model of this.
I’m impressed that cycles does such a nice job on the alpha stuff I’ve tried some other alpha channel truss textures and they worked quite well nice thing is the real time viewport is not bad too.
Thanks for taking a look and for the detailed clarification and tips on displacement.

The small piece worked OK on my machine, but having that expanded to the whole model will require too much memory. I would say it does not give any benefit over actually modelling the truss structure. If you want to do it the ‘easy’ way you could probably set up a Grasshopper definition that does all the finnicky bits.

That’s exactly what I’m doing but I wouldn’t by any means call it easy “I know I see your quotes”.