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Why ground polys?

seippg

seippg

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unitedstates
This feels like a dumb question but I've been hunting for the reasons for creating ground polys. Most of the docs I've found just assume that the reader knows they have to create them. I can create photoreal with SbuilderX without having to do anything and it's a large area. Does it create ground polys for me? What do they do and why are they necessary?

Thank you!
Gregg
 
Hi.

Ground polys are not mandatory, but in some cases, they can greatly enhance the environment at a precise location (an airport platform for example)
You can create photoreal terrain with Sbuilder X, and cover large areas. But let's say your airport uses ground markings that cannot be reproduced using either photoreal terrain (not enough resolution) or default ADE airport layout autogeneration. You can create custom and extremely precise ground pavement and markings with ground polygons.

You can also setup different layers of translucent polygons stacked one on top of another to create even more realistic scenery, without having to create all the necessary bitmaps at very high resolution (to save memory consumption) : Let's say you have a repetitive concrete pavement, but with different shades here and there. You can create a ground polygon layer as a base, mapped with the repetitive concrete texture, then add an overlapping translucent polygon mapped with a much less detailed shades of your entire airport layout. You'll keep the concrete details/orientation, and benefits from the shades variations all over the platform.

As already said, ground polygons are also used to draw custom ground markings, tarmac dirt and tarmac/taxiways edges, to make them blend well with the surrouding terrain.

Another usage of ground polygons is slopped terrain, or elevated platforms/bridges (in that case, they are usually platforms on top of 3D objects) Ground polygons being basically 3D objects that can be flat or not, you can control their shape and how they blend with the terrain, when the surface is supposed to be a "taxi-able" surface. 3D ground polygons are much more customizable than terrain meshes with photoreal terrain.

You use a 3D modeling tool to make 3D ground polygons (I use GMax, ASM and a compiler, and/or MCX)
 
A polygon is a two dimensional model to which you can apply attributes that affect how it renders in the simulator. A ground polygon has attributes that specify where it will render. You could map a photographic texture to a polygon and by joining it to a few other polygons and applying a few attributes, create a photographic ground polygon. To be clear, "3d ground polygons" are a different kind of polygon from "terrain meshes with photoreal terrain." Basically, if you can see something in the simulator, it is because it is a polygon and color has been attributed to it or a photographic texture has been mapped to it. Ground polygons do not have to have visual attributes, flattens and excludes are ground polygons that affect what other polygons will be displayed and how they will be arranged.
 
fsintegral said:
Hi.

Ground polys are not mandatory, but in some cases, they can greatly enhance the environment at a precise location (an airport platform for example)
You can create photoreal terrain with Sbuilder X, and cover large areas. But let's say your airport uses ground markings that cannot be reproduced using either photoreal terrain (not enough resolution) or default ADE airport layout autogeneration. You can create custom and extremely precise ground pavement and markings with ground polygons.

You can also setup different layers of translucent polygons stacked one on top of another to create even more realistic scenery, without having to create all the necessary bitmaps at very high resolution (to save memory consumption) : Let's say you have a repetitive concrete pavement, but with different shades here and there. You can create a ground polygon layer as a base, mapped with the repetitive concrete texture, then add an overlapping translucent polygon mapped with a much less detailed shades of your entire airport layout. You'll keep the concrete details/orientation, and benefits from the shades variations all over the platform.

As already said, ground polygons are also used to draw custom ground markings, tarmac dirt and tarmac/taxiways edges, to make them blend well with the surrouding terrain.

Another usage of ground polygons is slopped terrain, or elevated platforms/bridges (in that case, they are usually platforms on top of 3D objects) Ground polygons being basically 3D objects that can be flat or not, you can control their shape and how they blend with the terrain, when the surface is supposed to be a "taxi-able" surface. 3D ground polygons are much more customizable than terrain meshes with photoreal terrain.

You use a 3D modeling tool to make 3D ground polygons (I use GMax, ASM and a compiler, and/or MCX)
Click to expand...

=rk= said:
A polygon is a two dimensional model to which you can apply attributes that affect how it renders in the simulator. A ground polygon has attributes that specify where it will render. You could map a photographic texture to a polygon and by joining it to a few other polygons and applying a few attributes, create a photographic ground polygon. To be clear, "3d ground polygons" are a different kind of polygon from "terrain meshes with photoreal terrain." Basically, if you can see something in the simulator, it is because it is a polygon and color has been attributed to it or a photographic texture has been mapped to it. Ground polygons do not have to have visual attributes, flattens and excludes are ground polygons that affect what other polygons will be displayed and how they will be arranged.
Click to expand...

Hi Karl and Rick,

I think I'm starting to understand.

  • You can lay down repeated objects with textures for taxiways, runways, ramp, etc on top of lower resolution photoreal making the runways, taxiways higher resolution. You can use lower resolution shading on top to make them look more realistic. I assume the textures are made with Gimp or Photoshop and then used on the objects in GMax, Blender or 3DSMax.
  • The use of them as platforms on 3D objects is a bit mindblowing since it's not ground on a bridge. Scratching my head there.
  • Ground polys have the attributes to tell the sim where to place them. I guess ModelConverterX splits them up into smaller bits if you ask it to and stores the locations for each part within each part?
  • I read that if you keep the objects 100 meters or less in length that FSX/P3D will mold the ground polys to the curvature of the earth.
Assuming I have this right and from what I've gleaned from some tutorials on making airports is:
  • You get a photoreal from somewhere (SBuilderX, for example).
  • Get the big bitmap SBuilderX created and load it up into Photoshop, create water and blend masks.
  • Load the original photoreal from SBuilderX on a plane in GMAX, Blender or some other app, line it up carefully and create flat objects like concrete, markings as efficiently as practical.
  • Export the files and then import them into ModelConverterX and have it convert the resultant file into 100 meter or less ground poly chunks to be used by FSX/P3D.
I see some people dividing up their runways into 100M chunks in GMAX. Why do they do that since ModelConverterX handles the slicing up...or do I have something wrong?

Gregg
 
seippg said:
I see some people dividing up their runways into 100M chunks in GMAX. Why do they do that since ModelConverterX handles the slicing up...or do I have something wrong?
Click to expand...
There is no need to do that anymore. MCX does that for us automatically.
 
The use of them as platforms on 3D objects is a bit mindblowing since it's not ground on a bridge. Scratching my head there.
Click to expand...
I'm sorry, I'm not very good at english.
Let's say your airport has taxiway linking to the runway over water, and it's an actual bridge, not terrain. You build the bridge 3D in your favourite modeling tool, and export it (collision disabled). But it's just a 3D object, you cannot taxi on top of it. The second step is create a non visual platform (ie a surface that aligns well with your bridge, and export it (look at the gamepack SDK how to). At this point, there is not a single ground polygon involved. When you import your scenery in the Sim and have a look, sometimes you notice the bridge surface where it merges with the terrain (on the shore) flickers (graphic artifacts : sometimes you see the mesh texture above the platform concrete or asphalt, sometimes the the other way around). That's where ground polygons may play a role :
- either you've already built ground polygons (for taxiways, tarmac, etc.) on your airport, and just extend them a bit to cover the areas with the issue
- or create small ground polygons rectangles at each end of the bridge

3D objects textures and ground polygons aren't rendered the same way by the FS rendering engine (or graphic rendering pipeline, I don't know, I'm no expert) That's why trying to use flat polygons directly exported from the modeling tool won't work as expected, they are rendered as objects/buildings by the Sim, not as ground. That's why you use MCX to convert them, or do it manually with the appropriate (text) source files and compiler.


And yes, if you slice your ground polygons every 100 meter, it will follow the Earth curvature in FSX/P3D (but not in FS9 - FS9 is "flat"). MCX does it for you on "flat" airports.
However, on very slopped airports with chaotic terrain around, you may not have an accurate enough mesh, and may try to overcome that limitation with 3D modeled terrain environment. I call the principle that way because not all the surrounding has to be ground polygon : only the areas where you aircraft may taxi or fly a few feet above ground has to be ground polys. Anyway, at some point, and in this very case of terrain reproduction, you'll have to use ground polygons, and slice them accordingly to optimize the polygons usage (triangles) next to hills, holes, rifts and boulders, and still have the slice each 100 meter on the "quite flat part" of your airport platform.
 
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