Why are there are Trees on My Runway!
Many airports are out of date or not very well represented. It is common for folks to want to enhance their local airport. It is also common that in doing so trees and buildings end up on the new aprons, taxiways and runways. Sometimes the new areas of the airport are either above or below ground as well. This tutorial looks at the reasons for this and also how to deal with it.
Note that this tutorial is applicable to FSX and P3D. Different techniques are needed for FS9.
Getting Started
We are going to use KHUT - Hutchinson Municipal Airport - in this tutorial
KHUT in FSX
Take a careful look at the light brown area (1) This is called the airport background. All airports are going to have one of some size or another and cover the effective area of the airport. Airports in FSX are flat. It the real world there is pretty much no such thing as a flat airport since they all have to live in the surrounding landscape and truly flattening such a large ares would be impossible and not necessary. Runways at real world airports will have slopes and even humps and hollows. This is not the way it is in the simulator however. The light brown area is called the Airport Background Polygon and it is probably the most important terrain element that you will need. Things are a bit different in FS9 and that version of the simulator is not covered here.
KHUT in ADE
Airport Background Polys are not created using the same XML source code and compiler as the airport itself. While we can extract the airport information out of a Bgl file we can't do the same thing for terrain elements and that includes the Airport Background Poly (ABP). So the stock ABP is not going to appear when we open a stock airport. There is generally a good way to work out where it is though. If the airport has a boundary fence (1) then that is most likely to follow the edge of the ABP. Looks pretty similar doesn't it?
If there is no airport fence or you want to confirm the location of the ABP then you can connect ADE to FSX and move the user aircraft around the ABP in FSX and mark it out in ADE.
Map Out Background Poly via Flight Simulator
First connect ADE to your flight simulator. Check out this article if you need to brush up on how to do this
In the simulator slew the user aircraft to a corner or point on the background poly - use the arrow keys to slew
Lock ADE to FS.
Click the Lock Button. This will make sure that the aircraft symbol stays in the center of the ADE display and does not get lost out of view.
Add a Marker
In ADE select the marker tool
Move the marker cursor over the center of the user aircraft
Left click to add the marker
Repeat this until you have marked out the background poly
Chances are that your markers will line up accurately with the airport fence. So if there is a fence then you can safely use that as the boundary of the stock ABP
Save your airport project before going any further
Removing the stock airport background poly
Generally if we are going to work outside the existing area of the airport background poly then we will need a new one and it is probably better to first exclude the stock one.
Select the Terrain Poly Tool
Now create a small poly - a rough rectangle will do - but make sure it cuts the boundary of the airport background poly
- Select Exclude General for the Type
- Select Airport Backgrounds for the Tag
- Click OK to save the information
Compile the Airport
Make sure that the simulator is not running and compile the airport
Then start the simulator and go the the airport
Oops - buildings and trees all over the airport. So now we know that the airport background poly is what keeps all the autogen away from the airport
Add back the Airport Background Polygon
- Select the Terrain Polygon tool
- add vertexes for each corner point of the boundary fence or for each marker you added to show the boundary - remember to double click the last point to close the poly
- Set the Type to Airport Background
- Set the Tag to Flatten Mask Class Map ExcludeAutogen
- Save it by clicking OK
- Save your work
- Compile the airport and open it again in the flight simulator
NOTE: Make sure the leave the exclusion you made earlier in place to ensure the default ABP is not displayed
The Airport Background Poly is back - the important thing is that this is the one we added and not the stock one so it can be extended or changed to include any new features we want to put outside the stock boundary
Adding new features
I am now going to add some new features outside the existing boundary. I will add a new apron and some taxiways but we could extend a runway or move one or some existing feature
A simple apron and hangar outside the boundary fence. And like all good new construction sites the fence (1) stops folks getting in!
Save and compile the airport again (make sure the sim is not running) and then check out how it looks in the simulator
Here is our new facility but it is covered in buildings and some trees here and there.We also need to do something about that fence as well!
Extend the Airport Background Polygon and move the fence
- The extended airport background poly
- The new fence
Adding or deleting vertexes to an existing vertex based object
Modifying boundary fences and polygon edges will almost certainly need some more vertexes.
Highlight the fence or polygon boundary and move the cursor until the tool tip appears Ctrl + Left Click will add a new vertex that can now be dragged as desired. If you want to delete a vertex then select it and hit Delete. ADE will heal the line.
When you have finished your modifications in ADE: Save and compile the airport. Open it again in the flight simulator
And now we can see that the new area has a proper background, there are no trees or buildings in the way and the fence goes around it
Conclusions
In FSX and P3D it is the Airport Background Polygon that flattens the area and removes and autogen buildings and trees. We can't load the stock ABP into ADE but it is easy enough to work out where it is and exclude it. We can then add a new APB and extend it to cover any new features that are outside the stock ABP.
Fine tutor, it is very clear. Thanks a lot.