Howto:Convert objects with ModelConverterX

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NoteObjects that are uploaded to the FlightGear Scenery Database (and thus official FG scenery) must be released under the GNU GPL license. Most add-on sceneries from other flight simulators (X-Plane, MSFS...) do not comply with this license. Therefore, they cannot be included with the official scenery, unless the author granted you permission to release his work under GNU GPL, and you assured yourself that the contents he/she used are in public domain or otherwise GPL-compatible, or under his/her very own copyright. Basically, it mostly means that it is for your own private use only.
Note  As of April 22nd, 2014 there's not yet full compatibility with AC3D, so it might be better to wait for it to be fixed, to avoid the risk one's huge efforts not working with future versions of FG or AC3D. More on that below.

ModelConverterX (or MCX, project page here) is a freeware (not open) .Net Windows tool that can convert objects from a number of flight simulators. It can do batch conversion of models and their textures, if instructed so, changing also their name to upper case for better Linux (and other case sensitive OSes) compatibility. Thus, this potentially represent an easier alternative to Howto:Convert objects from X-Plane.

Download and installation

MCX runs on Windows and needs Microsoft .NET Framework version 2.0. It comes in two versions. One is the stable release, the other is the development release, with all the newer features, fixes, and bugs. As the cost of it is negligible, I suggest first trying the development version. The installation is nothing more than uncompressing the zip somewhere.

MCX can probably run on Linux too with a proper setup, but note that it uses Windows dependent code and such a setup will have to include WINE -- Mono alone won't suffice.

Support forum and official manual

A support forum for MCX is available at The official manual is linked in the cited forum, in this post, and is here.

How to convert

Wizards menu (click on the arrow to show the menu) > Batch converter...

MCX wizard menu

Then open the files to convert. You can select multiple files in the dialog. Remember to set the appropriate file type.

ModelConverterX batch converter, open dialog

Choose the output format, set an output directory, and check that Export objects radio button is selected. For the other operators check the official manual.

Then under the Operator box click Add... > Convert textures. On the right you'll be able to set an output directory for textures too (probably the same as for the models), choose the file format (probably PNG, or even DDS if you know what you're doing). For the other options check the official manual.

MCX batch converter - setup

The buttons at the bottom right are for saving/loading a batch converter setup, so that you don't have to add the files and set directories and operators every time. Very handy indeed, while experimenting.

Click Process button. Models will be loaded in the viewer and converted. There's no progress bar, so the only way to be sure it's done is to check the list of files in the Batch converter window: when it's done, the list will get cleared (not step by step). You might need to click "ok" on some dialogs during the conversion, so you'll better not leave the computer while converting, or you might come back to see it has been waiting all the time for you to come back.

Note that if a BGL contains more models, they'll have an AC file each in the output, with the model's name.

Working with the converted models

Let's just say that converting single objects is going to be a lot easier than converting a whole BGL compiled scenery.

AC format compatibility issues

As of April 22nd, 2014 MCX doesn't support very well AC3D file format. An AC model created in AC3D shows up in FlightGear with the X axis pointing south, the Y axis pointing up, and the Z axis pointing to the west. MCX doesn't convert to this coordinate system correctly, producing models that are upside down and 180° rotated on the horizontal plane in AC3D, and 90° counter-clockwise in FlightGear (yet, here they're straight up). Although to see the model correctly in AC3D you can temporarily flip Y and Z axes, and rotate it 90° CW to fix its orientation in FG, this issue leads to inconsistency in model editing (not sure if it's all MCX's fault).

You can follow the evolution of the problem here of FG forum and on MCX support forum.