Another texture mapping experiment...

[Philippe Hurbain]

Following my first foray in uncharted texmap country, I made another try, this time using Eomer helmet.
The big problem is to create the image for texture map. The part is not flat, so despite rather good lighting, it's not uniform, and plenty of reflexions. Moreover, printing itself is full of smudges. So you have to redraw the image anyway...

So I tried to kill two birds with one stone, and use LDraw Patterns Creator to create the drawing. OK, LPC is certainly not the most handy vector drawing program, but with it I obtained "old style" triangle based texturing of the part for comparison (and usage with MLCad...)
The next step was to generate images from the LDraw model. Easy...
- Open it using LDView
- In LDView options, disable lighting and edge lines. Set the field of view to a very low angle value (0.1°).
- Save a snapshot from the directions you want to project, with a transparent background. Here from side:

- You may want to show all conditional lines and make another snapshot. This shows the facets limits and will help to properly crop the image.
- Using an image editor, remove all areas that use main color, and crop your file to the area needed for mapping. For the helmet, I used two projections, one from front, one from side.
Here is the compared result.

Front helmet is the textured one, back helmet is the triangle-based texturing. As you can see, the good point of texmap is that LDView can do its magic and give a nice, smooth result.
Out of curiosity, I generated another version of triangle textured subpart, this time with conditional lines everywhere to force smooth shading. Result is smoother, but not as good as texture map...


Now, texture maps have their own problems...
- I still find it very difficult to derive correct values for mapping parameters. Theoretically it's simple, practically it's another story (maybe it's just that I have not yet got the hang of it...). The method I use is to create helper triangles to materialize projection area and when they are right, copy the values in texmap meta:

- For some reason, LDView properly smooth texmapped mirrored subpart... but not the other side!

- Even though the images I used are relatively high resolution, edges are not so crisp, and there is a slight fringe effect. It seems that partial transparency causes some issue to LDView. Here is an enlarged snapshot, showing that areas in transition region is transparent, instead of merging with main color. I even tried to use completely hard edge around image (helmet2.dat in attached files), the transition area is reduced but still there.
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Attached a zip file (renamed .txt to be able to post it here) containing the helmets...