Tips - 3D Modelling with Google Sketchup
The Google Sketchup∞
program proves the perfect tool to create high quality low polygon models. While the entire world is going crazy creating yet another model of their backyard, Google Sketchup is actually a very useful tool for low polygon modelling. In Sketchup you create geometry by drawing lines and arcs and extruding faces. Although it would be very challenging to create a smooth looking Boeing 747 fuselage, most objects don't tend to be that curved and are easily modelled in Sketchup.
For my Drive simulator project I needed great looking yet very low polygon count models. It has been a revelation to me to see how poorly even low poly game quality models are constructed so purchasing these proved a waste of time. But I have developed a way to create suitable models which I want to share with you here.
3D model creation is basically a 3 step process. I go out and take photo's of the the subject I want to model, then process these photos into textures and then I use these as a guide to model in Sketchup the result is a log poly count but nicely textured model.
First I take pictures from the subject I wish to model. As many as possible. For example pictures of a fire truck would include front, side and back pictures but also take reference pictures at angles that help you appreciate where things are relative to each other. After all Digital pictures don't cost anything. Top down pictures are usually harder to obtain but I tend to make up my own based on the images I already have.
A few tips when you take pictures:
- Stand as far away from the subject as possible and use your zoom lens to bring your subject closer. This way the perspective distortion is at a minimum.
- Outside subject are best photographed on an overcast day.
The next step is to process the pictures. I start by using the free and excellent program called Texture Studio∞ Download here∞
. This program allows me to make final perspective corrections and lighting corrections to the pictures and create new image files each nicely clipped and perspective corrected. Make sure to create these images at high resolutions because this is not your final texture yet.
Next I use "Paint.net"∞
to assemble a hi-res texture file. I import all the corrected images into separate layers and arrange them on a large canvas so that I make optimal use of a square space. The end result is a hi-res square bitmap containing all the sides of the subject. Save this image as your master texture image. This is the place where you go back to fix small issues in your texture if there are any. Now you can generate low-res textures at 1024, 512 and 256 pixels and save these as separate images.
Working in Sketchup
So now the texture is done. The next step is the fun part. Modelling in Sketchup. Start Sketchup with a new project and setup your dimension units. Then create a rectangle with approximately the same dimensions as the real world subject model. For example a rectangle representing the firetruck of 10 meters long and and 3.5 meters high.
Now you create a new material in Sketchup and you use your 1024 level texture or higher if your PC can handle it. Define the size of the texture as close as possible to the real world size.
For here it's fun. Just apply the material to a side of the cube and position the texture. Now it is just a matter of cutting out the outlines by using lines and arcs.
Tip: Make sure to reduce the line segment count of each arc because the face count can get very high. Also, as you create cut-out lines. Make sure lines don't cross other lines. Instead create two lines. One approaching the crossing and the next continuing from the crossing.
Google Sketchup is a pretty amazing 3D modelling tool but be warned, it has some real weird behaviours. The worst one being the fact that distorted textures are stored as a separate distorted texture image files. This is undesirable because these additional texture maps are unnecessary and fill up your texture memory on your card and thus slow down the model rendering later on.
Export the model as a 3DS file or OBJ file. I can recommend the OBJ file because it deals better with smoothing groups. The result should be the obj or 3DS file and one single texture file. Now, exporting is easier said than done if you don't have Sketchup Pro which is rather expensive to buy. However, there are tools out there that convert Sketchup's skp files to other formats. Otherwise just get a friend to convert your skp file for you or even simpler. Install a trial version of Sketchup Pro. You get 5 hours unrestricted use which if used exclusively for model exporting will last you a very long time.
Now you can replace the hi-res texture with the lower res versions of the same texture. You'd be surprised how good a 512 or 256 texture can look on your model and again it makes the model more efficient. This image is displayed in a GLScene application. loaded as an OBJ file with a 512 pixel texture and has 342 faces.