WIP: Steamboiler as an example for projection rendering (Part 8)


Well-known member
Edit: The boiler is soon available on the DLS

The mesh is finished, the low polygon object is mapped.

Some statistics.

The high polygon model has 232.188 polygons and 132.438 vertices:

The low polygon model has 16.021 polygons and 8.719 vertices.

The picture below (from 2048x2048 reduced to 800x800) is the final render template into which all high detailed objects will be rendered via projection:

And this is how the low polygon model looks for now in Trainz:

So lets start. First I will render the rings around the boiler hull and then, step by step, each in a seperate render process, all other details. Why this and not all together?
By doing it this way, I will get for each detail a single image which has later also a single layer in Photoshop. With the magic wand tool I will select all pixels of a value of 0, 0, 0 (black) and remove them, so the background will be transparent. By doing this, there are no areas which overlap other details with the background color.
But be careful, that layers which contains details that covers other details are not below their layer in the layer hierarchy! E.g. the layer with the rivets has to be above the layer with the rings around the boiler hull.
If later I want to edit something (waethering etc.) it is much easier to do, if you have each relevant part in a single layer. This method will take much more time and effort, but I prefer a maximum level of control over the final image…

A hint, sometimes with a complex model like this one it can happen, that parts of the projected objects are rendered to places where they don't belong. This can be avoided by using the cage. But as I mentioned before, there are some problems with artefact using the cage. I find it easier to simply detach the relevant polygons from the low model and do the projection rendering on them. By using the render option Use Existing Channel, the mapping always fits. Later they can be attached again (do not forget to weld the vertices again!), only the smoothing has to be controlled afterwards, because attaching objects can destroy the smoothing. To make controlling of the smoothing easier, simply use in the Tools tab UVW Remove->Materials(Set Gray). NEVER click on UVW, otherwise all your mapping is gone!

Okay, step by step.

1. All mesh objects are completely ready, mapped and do not need any corrections!
2. I prefer all high polygon objects pooled in small units, which later shall be projected onto the low polygon object.
3. Check again your GI settings. Set all render options to a very high level.
4. All objects shall be visible now.
5. Now I select the low polygon object, go to Polygon Mode and select a set of polygons on which I want to project a high polygon object. E.g. I choose the middle part of the boiler hull, detach the polygons as object01. Now I select object01 hit the '0' key, choose a diffuse map and a bump map as output. Next I select in the Render to Texture dialog -> Projection Mapping -> Enabled (ON) -> Pick the desired high polygon objects and render them.
6. In my case I have now two image files: Object001VRayCompleteMap.tga and Object001VRayBumpNormalsMap.tga
Now I load these files into Photoshop, where the file with the basic mapping above is already loaded. With the Magic Wand I remove the black color and with Paste Special -> Paste in Place I copy the result to the basic map.
This I do with all objects.
As a result I have a Photoshop file with many layers which I can edit very easy. I also group all normals map layers and all diffuse layers each into one group.

If all layers are complete and correct, I make a copy of a group and reduce the copy to one layer.

7. In the end all detached objects are attached back and the vertices are welded. If all the things are done, I create a new standard material named blabla.m.tbumptex and fill the diffuse and bump slot with our Photoshop work, apply the material to the low polygon mesh, use the Unwrap UVW modifier and load the uvw file and we are done.

This is how our beauty look like in Max:

And this how it looks in Trainz:

Quite dark and some layers still need some color adjustments, but the purpose of this tutorial was not to create a perfect asset, but to describe how to reduce polygons without relinquish details…

modeltrains;bt2545 said:
Looking good Mick! Great work :).

Thank you! I hope this tutorial is of any use for someone&#8230;


P.S.: I played again with some color values and now it looks like this in Trainz: