P3D v4 Grass as autogen on airport backgrounds

According to the P3D v4.2 release notes a new feature of the SDK is that "grass can be added as autogen on airport backgrounds". Has anyone figured out how this is actually done yet?



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Would be interesting to know indeed. If it's just a new autogen model or some new feature in the autogen. I haven't looked into it yet.


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I did check the SDK last evening and looked in the sim, but I haven't found any information about this new feature yet.
After a fruitless search myself, I did assume that this was a new Speedtree model. I can remember someone talking about large coverage of SpeedTree grass a while ago. Maybe I need to install the scenery update, which I normally keep away from...
Like a lot of simmers, though, I don't use Speedtrees because of the colour issues.


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But even if it's a speedtree, there should be a way to assign it to your grass. We should be able to find that.
Yes, a new technique would be a great thing, but this specific wording was what made me think of Speedtree -- maybe the reference to 'airport backgrounds' is some sort of caveat, that it be restricted to airport backgrounds only, so that we don't all cover the world with 3D grass:)


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So then it would be linked to the terrain vector definition of the grass background. Could be....

Still interesting to know where it is and how we could use it. It sounds like something we developers have to do, not automatic for all airport backgrounds.

With the annotator you can find a 'grass' entry. It contains grass (weight 99)and some bushes (weight 1) but the {GUID?} is 0000-0000-0000-0000.
Would that mean you have to put in your own grass model(s) perhaps?


dave hoeffgen

Resource contributor
I could imagine grass as AGN polygon vegetation, even in previous P3D versions and FSX.
A developer would need to define the vegetation class on his own of course.

However this would only work for photoreal airport backgrounds.
For a vector polygon it would mean the "afcad" needed to locally suppress the autogen and according to the "glitch airfields" in FSX we know that's not the case.
But maybe this is the innovation in v4? :scratchch
The only clue that I have found is that there are SpeedTree texture files entitled Backyard_Grass_*.dds located in the folder <drive>:\Program Files\Lockheed Martin\Prepar3D v4\Scenery\Global\texture. Since the ST model library BGL is "encrypted" in some manner, it makes sense that LM hasn't given any responses to questions about autogen grass on its official message boards.

Has anyone tried to place the corresponding model with P3d4 SimDirector?


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Well, even if the library is encrypted, it would make sense to tell developers how to use the new feature, instead of only having that single line in the release notes.


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I think the bgl format is the same, there are just no normal mdl models inside, but specific speedtree models.

Although I do not yet have P3D to study this apparent "new" feature, I should think that the online P3Dv4 documentation would specifically address this if there was a change to the Airport type of CVX Vector object definitions in Terrain.Cfg; thus far the "Airport Background" object type appears to be identical to prior versions of P3D:



IIUC, "Airport Background" is a specific sub-type of CVX Vector object compiled via SDK SHP2VEC with either 1. 2, or 3 GUID-referenced attributes, but is AFAIK, otherwise a "Park"-type CVX vector object which can be textured- or not textured- depending on its Land Class type; and if textured, it may be possible to annotate it with Autogen just as can almost all other default or custom textured CVX vector objects.

"Although this area is titled Airport Boundaries, these are used for a number of purposes, including flattening a surface and excluding certain types of data, in addition to defining airport boundaries."

https://www.prepar3d.com/SDKv4/sdk/world/terrain/terrain_overview.html#The Shp2Vec Tool

The "Airport Background" as a specific sub-type of CVX Vector object compiled via SDK SHP2VEC is, of course, distinct from BGLComp-XML-compiled "Airport" poly-line and polygon objects such as 'Paths', Taxiways, Runways (and certain other objects / features) that have special attributes and additional functions within the MSFS / P3D "Airport" sub-system of the rendering engine, and IIRC, are textured with legacy-format *.R8 textures which can not be annotated with Autogen.

However, since default CVX vector Airport Background objects created with the "MaskClassMap" attribute may- or may not- end up with a locally-compatible type of default land class that has any Autogen annotation, one must try to determine whether to use that type of object instead of a custom CVX vector object with an assigned texture that accepts Autogen annotation when it is desirable to do so.

Luis Feliz-Tirado detailed the MaskClassMap mechanism, and a cross-walk table for textures which will be "mapped" as a substitute for Airport Background CVX vector polygons that use the MaskClassMap GUID type are documented in a spreadsheet file:

[Luis_Feliz-Tirado_Terrain_Design_for_Flight_Simulator_X install path]\Additional_documents\Airport_ground_mask.xls

...inside this downloadable tutorial package:

Terrain Design

File Description:
Terrain Design for Flight Simulator X

This simple illustrated document explains the basic concepts in Flight Simulator X terrain, and how to change them using SBuilder for FS X. Make new water bodies, roads, vehicle traffic, airport flattens, remove autogen, add more detail - anybody can do it easily and quickly.
My most sincere apologies - I am unable, for lack of free time, to offer support of any kind. For questions or problems, please post in the Avsim scenery design forum.

Filename: terrain_design_for_flight_simulator_x.zip
License: Freeware
Added: 14th December 2009, 13:29:15
Downloads: 16648
Author: Luis Feliz-Tirado
Size: 3991kb


Helli Hauck of the ADE team has detailed some aspects of the MaskClassMap sub-system and importance of "Layering" here:



Jim Vile has previously explained this option to utilize various default and custom types of textured CVX vector objects at airports (...instead of the all-too-common practice of making an airport background object as a big 1-piece polygon).

Jim Vile's approach to building airports by "segmenting" the Airport Background polygon & other airport ground objects (flatten, Apron etc.) is linked from here:


See: "NOTE: Jim Vile's tutorial is IMHO one of the best on the airport background polygon creation process:"


Some other additional linked discussions:

* MaskClassMap features


* Arno and others on factors involved in Autogen being allowed to "pop through to the top" from *an.AGN files mapped to other land class layers below top-level custom photo-real aerial imagery land class:


* Holger, Arno and others on factors involved in aggregate display of Autogen from multiple super-imposed land class layers (including those that underlie a 'top-layer')

NOTE: Use of Blend Mask values that yield excessive transparency with custom land class objects ...may produce surprising results ! :alert:


Hope this info helps when considering use of Autogen annotation for FSX and P3D "Airport Background" CVX vector objects. :)

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