One of the topics that is discussed often lately on the FSDeveloper forums is using Sketchup to model for FSX. The good news for those of you who think that the learning curve of GMax is a bit too steep, is that you can use Sketchup as well if you want to model some scenery objects for FSX. I should directly note that if you plan to make an aircraft than Sketchup will not be of much use to you, since you will still need GMax to do all the animations and other advanced features that an aircraft needs. But if you want to model some scenery objects (without animations), then using Sketchup is certainly an option for you.

In this blog post I want to discuss some issues that you need to be aware of when modelling using Sketchup, as there are still some open edges. Later I plan to write a tutorial about this as well, but I need to do some more research on a few topics.

How to export to FS?

You can not export directly from Sketchup to the MDL format that is used in FSX for objects. But in Sketchup 7.1 you can export directly to the COLLADA DAE format (in earlier versions this was not possible in the free version, only in the Pro version). Once you have the COLLADA file you can use my ModelConverterX tool to convert the COLLADA file to a MDL object for FS. This MDL object can then be put into a library and positioned like any other MDL object.

But what about the textures?

Using the ModelConverterX it is indeed easy to convert the geometry of your object, but how about the textures? Most of the texture you applied in Sketchup will be exported a JPG files and that is not a format that FS can read. So you will have to convert these manually to the DDS or extended BMP format as used by FS. Also be aware that the textures as exported by Sketchup not always have sizes that are a power of two (you know 256×256 or 512×1024 or …) so you might have to resize the texture as well before you can use it in FS. I am working on a ModelConverterX feature to assist you in these texture conversions.

Watch out with the drawcalls

With Sketchup it is very easy to create your geometry and it also comes with a library full of materials, for example bricks or roof textures, that you can just drop onto your object. But wait a second, that means you will end up with a material that uses many textures (and maybe also some colours) and that will not give you best performance in FS. Each of these will add an additional drawcall to your object. So I would not advice that you model like that for FS.

But how should you model then? It is best to try to use only one texture sheet for all parts of your object. So don’t use these materials and do not apply a colour to your polygons. Try to use the same material on the entire object. I know it will cost you a little more time to map the material correctly, but it will pay you back in a better performance within FS.

Also be careful not to use the “make unique texture” option in Sketchup, as that will cut your texture into smaller pieces and then you still end up with multiple textures (even if they came from the same texture sheet).

Checklist

So sum up all these items and place them in a checklist you would get the following lists of items that you need to do when you want to use Sketchup to model for Flight Simulator:

1. Create your object in Sketchup. Be aware of the performance implications when working with materials, so try to use one texture sheet for the entire object if possible.
2. Export your object from Sketchup to the COLLADA DAE format.
3. Import the DAE file in ModelConverterX and export it again as FSX MDL file.
4. Convert the textures that Sketchup exported to a format that FSX can read (DDS is preferred). Be aware that you might have to resize them so that the sizes are a power of two.
5. After that you can use the MDL file and the textures like any object for FSX, so you can put it in an object library and place it with your favourite object placement tool.

And most of all, have fun! In the end you should notice that it is a lot of fun to make your own objects for FS and if you found the learning curve of GMax to steep, then Sketchup might be more fun for you to use.