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scott967

Airport backgrounds - AB

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It happens that some unfortunate user will suddenly find his favorite airport chock full of trees, obstructing runways, taxiways, and ramps, making flight somewhat more challenging.The experienced members of this forum will immediately recognize the dread "missing AB" problem. This is where the grass skirting underlying the airport has somehow been misplaced, thereby allowing the land class to display its autogen.This skirting, or airport background, is to be found in the AB files. Each skirting has the exact shape of the airport flatten (FL) and is located in the same place, unsurprisingly, as the flatten.The solution, as many know, is to either find the missing AB file, or to simply create a new skirting using a non-autogen ground texture, (such as grass!), to replace it.There is another solution, of course, and that is to exclude the autogen. A simple matter thanks to Paavo Pihelgas and his ExcBuilder. The only disadvantage to this is that the ground under the runway will be that of the surrounding land class, which may not be what you want.However, I have used this solution in my private strip, placed in the middle of tropical forest textures. I prefer that ground to simple grass - here in the tropics, one is advised to mow often, or it all becomes jungle-like after a few weeks! For fun, I excluded only the autogen trees on the hard surfaces, and left trees at the ends of the runway:http://forums.avsim.net/user_files/141736.jpgThis makes for very challenging take-offs and landings. Only very good pilots can use this strip or they will rip their wings through the trees (and I do, often!) A lot of torn Ceconite here.In other places, I have used the grass and it does look very nice and prevents autogen from displaying:http://forums.avsim.net/user_files/141737.jpgIn that instance, I used two layers, one of dirt below and one of grass for this very interesting effect. More realistic, I think.Out of curiousity, I went to the trouble of taking apart a default file for my region just to see what is used for skirtings. (Yes, I know, I am a hardened criminal, and deserve the worst penalties of the law for my repeated decompilations. I have a mind to turn myself in to the Microsoft legal department, in hopes of getting the substantial reward that they offer.)To my surprise, in the entire region, only 3 textures are used: - 1189 - Low Sparse Grassland; - 1191 - Cool Grasses and Shrubs; and - 1196 - Semi Desert SageWell, this was a surprise, particularly the Cool Grasses and Shrubs. An unexpected sight in the Caribbean, where it has not been particularly cool for the last 5 million years.But, I wasn't put off and, in another project, made a new AB using the same texture as the default, that is, the very same Cool Grasses:http://forums.avsim.net/user_files/141738.jpgThis has some interesting features. Notice, please how the green grass varies to brown dirt somewhere in the middle and then becomes grass again.I don't remember exactly seeing one of the ground textures that looks like that, so I consulted the terrain.cfg file for more details. Supposedly, this is the entry:Texture.1191 // Cool Grasses and ShrubsType=1Size=4ExcludeAutogen=1MaskClassMap=2Some extremely interesting things in there. Obviously, it excludes autogen and the size is 4 meters per pixel. But why is it type 1?For your information, the VTP lines use one of 3 different types of textures. Here is a type 1, as taken from the S.D.K.:http://forums.avsim.net/user_files/141739.jpgThe texture is divided into 4 equal vertical segments that are then applied to the line. Please disregard the yellow lines, included for demonstration purposes only.But, does this mean that airport backgrounds are VTP lines? Preposterous.In addition, all entries in the terrain.cfg should indicate the texture to be used. For example, the road, stream, shoreline entries all indicate a corresponding texture or textures, including all seasonal variants, such as:Texture.1086 // lake / bank / surfType=2Size=4ExcludeAutogen=1MaskClassMap=3Textures=o_blackrock_ls.bmp,o_blackrock_ls_hw.bmp,o_blackrock_ls.bmp,o_blackrock_ls.bmp,o_blackrock_ls.bmpEffect=lakewavecontrollerBut, none of the airport backgrounds include this information. Not a one.Well, I have looked and looked, and have not been able to find anything like that Cool Grasses. The land class value 40, which corresponds to ground texture 09, does not look a lot like that at all, plus it is not a type 1 texture.I did find a type 1 texture, runway03.R8, that looks something like it:http://forums.avsim.net/user_files/141740.jpgalthough not quite. And anyway, it is a RAW image, so what would that be doing there?In short, the whole thing is somewhat baffling and I would appreciate any input as to the source of the textures for airport backgrounds.Best regards.Luis

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Great post Luis. I would like to add an other reason for those trees appearing in the first place. It could also be that you have a VTP exclude active in that area that removes the default grass. For example because the exclude covers a slightly bigger area than intended.

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Hi Luis,interesting observations. Here are a few of my thoughts based on reading the SDKs.* Texture Type has a default value of 1; it's possible that it has no meaning with airport skirtings but is still set to its default value* MaskClassMap is the interesting parameter as the Terrain Config File SDK states "Use for airport skirting polygons". It is responsible for blending background landclass textures with the AB VTP2 poly; the resulting "mish-mash" is sometimes called the Chameleon effect ;-)* The comment behind the Texture.### gives you the hint which texture is used by AB*; the verbal description is the same as the list in the landclass tables. The SDK isn't helpful in this case but Gerrish Gray's EXCEL spreadsheet is. Thus, "Cool Grasses and Shrubs" translates into LC 40, which is the 009*.bmp set. Incidently, all of the texture types used have no associated autogen.* unless it's an exclusion issue like Arno suggested what you see is likely the blending effect between LC 40 and whatever LC is used in the area. One way for testing this is a top-down view because that would reveal sharp lines with excludes or VTP2 overlays vs. soft edges for blending.* the other option for experimenting is to set MaskClassMap temporarily to "0", which would prevent any blending. Remember, this is what we used as a patch before 9.1 came out to prevent the CTDs due to too many blening operations in a single LOD13 cell?Hope that helps a bit with the riddle.Nice airfield scenery you got there!!!Cheers, Holger

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Thanks for the comments, guys.The plot thickens. I drew a few supplementary polygons and assigned the 3 supposed AB textures and this is what I got:http://forums.avsim.net/user_files/142071.jpgNo matter which is used, it all comes out as grass!In addition, and as Holger points out, type 1 is a default VTP line setting. But, airport backgrounds are not VTP lines, so that setting should not appear in there at all.Interesting comment about masking the texture. As you can see from the image, the land class surrounding the texture is all urban, no dirt. So, why does dirt appear in that airport background? This is one of the mysteries of life.Tentative conclusion: DO NOT USE. That is, this feature may well not yet be implemented in FS, and any airport background that you use will turn out to be grass for the moment, same as the shorelines in the previous version were all tan sand.Of course, I have not tested all the variants of airport backgrounds, nor in all the regions, so nothing is definite.And, I still wonder where the dirt comes from.Best regards.Luis

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Thanks for posting and playing around with this. I have always been curious about how the terrain.cfg numbers for AB get translated to specific textures. I assume it's hard-coded somewhere?scott s..

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