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Ground Polys in FSX - Clarification Please

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gadgets

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There are numerous posts on this subject. But, I am still a liitle unsure about two aspects. Hopefully, rhumbaflappy or one of the other gurus out there will see this.

First, I am aware of the recommended size limit for ground polys of 100m. But, it's not clear to what this 100m applies. I presume it is the maximum distance between any two vertices in a poly, i.e., no vertex in the poly is more than 100m from any other vertex in that same poly. If so, one should be able to have a very large ground poly comprising of a number of polys which comply with this limit without difficulty. But, there are so many posts suggesting ground polys be "broken" on 100m boundaries (and Arno is working on as tool to do this) that I am beginning to question my own interpretation.

Second, there seems to be a suggestion that where a ground poly comprises several layers, the layers should be numbered in steps of 4 or more. I have been using 6-layer ground polys with layers numbered 5,6,7,8,9 and 10 for some time without apparent difficulty. Do I have a "disaster" just waiting to happen?

Don
 
Don,

I can answer the first bit .... you just need vertices close enough together that the poly can be conformed to the ground.
For a flattened piece of ground this means 100m or less apart. Slicing up existing geometry can achieve this.
I have had some success with non-flattened areas, but you need considerably more vertices.

With the issue of layers .. I'm not sure this is a problem at all, but there may be a different opinon on that.
 
Hi Don,

I think those layers in steps of 4 is a habit from FS2000 or was it FS2004 :). Not sure if FSX still requires it, your results seem to indicate not.

About the 100 meter. I usually split my polygons every 100 meter. Of course the long edge of the triangle would still be more than 100 meter in that case, but I haven't seen problems with that.

If you keep them in one reference point, the splitting has no problems. You won't get cracks or gaps. That only happens if they are in multiple reference points. Since the formulas we used to use for that in FS2004 no longer work correctly.
 
Thanks, guys. But, unfortunately, I still don't have the answer I was looking for. I guess I should have been more explicit in my query.

I use multi-layered FS8 ground polys to lay down apron markings and illumination. In both FS9 and FSX, I use layer:
  • 5 for the base - usually asphalt (which, admittedly, I could have drawn with ADE as aprons)
  • 6 for roads
  • 7 for other features such as gardens
  • 8 and 9 for lines
and, in FS9 only, 10 for ground illumination planes.

I've noticed no ill-effects from this numbering scheme in either FS9 (for which it was created) or FSX.

Each layer is comprised of a number of individual polygons. All layers share a common reference point - which may be outside the bounds of the ground poly.

Using the CYYJ terminal area poly as an example, in almost all of the individual polys, no vertex is more than 100m from any other vertex in the element to which it belongs. The only polys that violate this are: the vehicle parking lot, a couple of roadway segments and a long white line. The reference point is the same as the for terminal itself (everything derives from the same Gmax file) which is well outside layers 9 and 10 which deal only with the apron.

So, my question is: Is it sufficient to split only those large polys into a series of smaller polys where no vertex is more than 100 m from any other, or must I split each of the layers along 100m boundaries - which will create many more vertices and, hence, overhead and make future modification more difficult?

Don
 
Hi Don,

If polygons already have vertices no more than 100 meters apart, there is no need to split them again. So in that case you would just have to split the long ones.
 
Thanks, Arno. That was the answer I was hoping for.
Nice new picture.

Don
 
re: layer numbering.

Maybe some one has better info, but back in FS2000 scenery sdk it described the scenery category system:

There are 64 categories in the category system of which the following are defined and
used:
CAT_MESH = 4
CAT_POLY = 8
CAT_RIVER = 12
CAT_ROAD = 16
CAT_LINE = 20
CAT_RUNWAY = 24
CAT_MOUNTAIN = 28
CAT_CRATER = 32
CAT_GROUND_ELEMENT = 40
CAT_SHADOWS = 60
Categories are processed from lowest number to highest (0-63).

Then in FS2002:

Layers define the order in which Flight Simulator applies the textured polygons to the ground and in which phase of the texture building process they are applied.
• Layers 0 to 3 are applied in the water texture layer. These are applied before the water texture is masked into the land texture. These polygons appear only in the water and are clipped by the land portion of a texture.
• Layers 4 to 7 are in the land texture layer. These textures are applied to the land texture before the water texture is masked in. Polygons used at these levels appear on the land texture but are clipped by the water portions. For this reason, airport skirtings and park polygons were placed in layer 4.
• Layers 8 and above (the number of layers is capped at 100) are applied to the texture after the land and water are masked together. Polygons applied at this level appear over both the land and water portions of the texture. Shoreline polygons were placed at level 8 to provide a blending effect between the land and the water.
The following table lists how the layer values are distributed.
Type of Data Layer ID
Water Texture 0 – 3
Land Texture 4 – 7
General 8 – 100
The following table lists the layer values used in Flight Simulator 2002.
Type of Data Layer ID
Airport Skirtings and Parks 4
Shorelines 8
Streams 16
Dirt and Minor Roads 31
Major Roads 32


AFAIK the "divisible by 4" rule was just a convention suggested around the time ground2k was the main tool available for terrain work.

scott s.
.
 
Thanks, Scott, I have the FS200 SDK but never thought to look there. (It is my primary guideline for decoding BGLs.) Presumably, the stepping by four was simply to leave room to insert other categories if necessary.

I didn't get involved with FS until FS9, which didn't adhere to this convention. Matter of fact, in FS9, it seemed everyone did his/her "own thing" with layer numbering subject, of course, to lowest before highest.

Since my current layering scheme seems to work in both FS9 and FSX, I'm going to leave it alone. But, Anro, I do plan to break up those big polys.

Thanks all for the clarifications,

Don
 
Hi,

gadgets said:
Nice new picture.
Click to expand...

mmann said:
The smile looks like it took a little more effort too
Click to expand...

My wife kept insisting on me changing the picture. She says this one looks more like the normal me :).

The previous picture was taken on a day at the aircraft firing range. The whole days with F-16s, Tornado's and helicopters flying around. That explains the big smile :D.
 
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