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Howto:Place 3D objects with the UFO

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The UFO aircraft is a superb tool for placing a new (or old) 3D object at any arbitrary location in the scenery with just a few clicks of the mouse.

Placing objects in the scenery is a really easy way to contribute to the FlightGear project. It doesn't require any programming knowledge, and you can contribute something valuable in 15 minutes.

Choosing your object

The first thing you need is a 3d model to place in the scenery. The FlightGear Scenery Database (http://scenemodels.flightgear.org/) maintains a huge library of generic models, which will have been included in your FlightGear installation.

If you have created your own model you need to save it to somewhere the UFO can find it. The UFO searches for objects under the Flightgear/data/Models/ directory. Let's say you have created a CAT III marker, called catii-iii.xml. In this example, we create a subdirectory called Tabu and save our catii-iii.xml there.

If creating your own object, make sure it is the correct size! In Blender, units are meters and the Caliper script may help. Note that you should not use Google Earth to determine the correct size. See here and here.

Selecting the ufo

Placing objects with UFO html m49fbed81.jpg

Now start Flightgear, and choose UFO as your aircraft.

Placing objects

Once Flightgear has been started, fly with the UFO to the place you want the model to be positioned.

Note that you should not use Google Earth to determine the correct position due to licensing problems. See here and here.

Placing objects with UFO html 5fa8d7b1.jpg

Let's say we want to position the catii-iii.xml object at the end of a taxiway. We stop the UFO just above this intersection and press the space key, a Select Model window will open up where the contents of the Flightgear/data/Models/ directory will be shown. Select your model from this list, then close the window. The selected model path/name will be display in green text at the bottom left of the FlightGear screen.

Placing objects with UFO html m184fb381.jpg

To place the object, simply left-click on the position that you want to place it. By default it is placed completely horizontal and rotated to point North. It will probably not have the correct orientation and it will be partly covered by the surrounding terrain, but we can adjust that.

Placing objects with UFO html 12ee70a1.jpg

Rotating objects

Fly closer to the ground with the UFO, so that you can see it better.

Now press TAB (or Ctrl-I), and use the resulting sliders to adjust the latitude/longitude/elevation/heading of the model.

Placing objects with UFO html 439816e9.jpg

See the UFO from the 'White Project' of the UNESCO page for more information on the UFO command keys and exported file locations, or press ? while in FlightGear.

Exporting the result

Now that the model is correctly positioned, press the D key to dump the model position data to the terminal. A few lines will be printed on the console, providing the necessary orientation data.

Placing objects with UFO html m4cf0cbf7.jpg

The most important lines are the last ones:

# e000n50/e008n50/3089154.stg 
OBJECT_SHARED Models/Tabu/catii-iii.xml 8.57928135 50.03667992 105.9972 111.1

The first line identified the location of the scenery file for the object. The OBJECT_SHARED line indicates the objects name, longitude, latitude, altitude and orientation. This can be read by FlightGear itself and can be (submitted) to the FlightGear Scenery Object Database.

You can also save these coordinates into your own scenery file so that your changes will not be lost the next time you start FlightGear.

Saving the changes to your scenery

In the terminal window, you get three sections printed out by the UFO with very detailed information about what's going on. We need the lines at the end.

As noted above, the UFO helpfully exports the name of the scenery file where the object's coordinates have to be saved. In our example

e000n50/e008n50/3089154.stg 

The default location for scenery files is Flightgear/data/Scenery/Objects/. Simply open the referenced .stg file, add the OBJECT_SHARED line to the bottom and save the file. Now you have your object's position saved, and it will appear inside the scenery every time you start Flightgear!

In our example we would open 3089154.stg in Flightgear/data/Scenery/Objects/e000n50/e008n50/ and add the following line.

OBJECT_SHARED Models/Tabu/catii-iii.xml 8.57928135 50.03667992 105.9972 111.1

Saving to XML

Alternatively, if you press the E key while developing scenery with Ufo, fgfs will generate an xml file with the dump of your current work in a "ufo-model-export.xml" file. You can later reload this XML file with --config= command-line parameter:

Example for Linux:

fgfs --config=$HOME/.fgfs/ufo-model-export.xml