Qgis2threejs | A QGIS plugin to export 3D maps to Web

I would like to know if anyone knows how to make a map overlap a DTM (digital terrain model) ou DEM.

For my part, I used QGIS plugins openLayers and QGIS2Threejs. The problem with this method lies in the resulting 3D model export : no UV is exported, I only get a .dae and a .png files (no mtl file to link them). So when I load the .dae file in 3DS Max, the texture is nowhere to be found. I have to add it manually and make the UV mapping myself... But there is nothing precise in that. Only then can I export a folder containg .max, .mtl and .png files, and proceed to the next steps.

Does anyone know another method, more accurate ?

Problem:
I have encountered major issues with performance with regard to a scene rendered with Three JS. The problem concerns rendering a large number of simple geometries (11,107).

(edit) Each building has a unique height based on elevation data, a unique shape based on their outline, and a material of 5 possible options depending on the size of the area they take up.

I have isolated the issue in the first scene below, the second link provides context. Turning off the polygon buildings in the second link illustrates the drop in framerate that the layer is causing.

Preview Image

• View 3JS Render (Polygons Only)
• View Entire Scene

How polygon attributes were determined:

Each polygon has a uniform height, but unique shape based upon a building footprint. Furthermore, each building is assigned a colour from a gradient relative to the size of its area (large yellow, mid red small purple). As a reference, this was achieved in a geographic information system before being passed to ThreeJS (QGIS, with QGIStoTHREEJS plugin).

Attempted Solutions:
I have focused on trying to merge the polygons geometry to reduce the number of render calls. However, because each polygon has an assigned colour I have faced issues applying the appropriate materials and mesh. I am struggling with the logic of how to do this in context of the two loops in operation.

Relevant Code Snippet:
The full source can be found here, and a download of the working code is available here. This snippet is from lines 1935 to 1987.
I have trimmed the ThreeJS source to what is relevant to my issue.