FSXA Water Polygons at QMID levels 7 and 11

#1
I want to understand the logic here and will be grateful if somebody can explain the difference.

I've started my (little?) photoscenery project here, which eventually should cover two small islands shown on the image below. I have the necessary tools to start with the terrain design first - SDK, SBuilder, Arno's great tool-set, etc. and am reading / learning a lot both here and from SDK.

Now, from what I understand reading the relevant section of Terrain SDK, the FSX vector data clips at QMID level 11. I've successfully tested this behavior making a water polygon, filling it to QMID11, cutting a hole in it to avoid flattening the underlying terrain mesh and (!) assigning proper altitudes to each shape point thanks to TMFViewer, which gave me the surrounding altitudes at sea level. So far it looks good since I've managed to get rid of the default FSX textures, shorelines and to retain the island elevation.


What I'd like to know is why the default CVX file covering the same area (see image) is made at QMID7 level. I know this fact is mentioned in SDK but for practical purposes, I'd like to know the difference between filling the QMID7 and QMID11 areas with water polygons. For if I can fill in a smaller area (QMID11) and avoid extra workload associated with extraction of default vector data for the area I'm not focused on and re-applying the extracted data to my CVX file, why bother?!

Thanks!
 
#2
Hello:

ACES uses various LOD sizes to fill hydro areas using entire quads within the FS terrain grid, so that as one defines mask edges for land and water masks, one begins using progressively smaller quads and Area Point 'mini-quads' until one is placing vertices for poly-lines and/or polygons inside LOD-9 / QMID-11 quads.

The FS rendering engine has certain default 'granularity' chunk sizes for terrain scenery content at which it prefers to determine where objects should be displayed or "clipped".

Generally, LOD-9 / QMID-11 is the quad size at which vector scenery content is to be "clipped", and SBuilderX has features that assist in working with that quad size.

One typically should use LOD-9 / QMID-11 as the quad size in which to group and clip edges for vector scenery content in FSX / P3D.

For FS2Kx legacy vector scenery content and FSX / P3D land class polygons, however, one may see that ACES uses a LOD-5 / QMID-7 sized quad.

It is possible, however, to individually exclude specific types of vector scenery objects within LOD-9 / QMID-11 quads without requiring replacement of all content within a particular quad via the proper GUIDs, which allows one to minimize use of the "Exclude-and-Replace-all" mechanism that otherwise works at the level of the entire quad . :)

GaryGB
 
Last edited:

HolgerSandmann

Resource contributor
#3
Hi Rustam,

Shp2Vec.exe automatically clips all input Shapefiles, both vectors and polygons, to the QMID11 grid. You can see this by loading your local default CVX .bgl file into TMFViewer. That the default files tend to cover QMID7 cells is probably simply to keep the overall file numbers manageable. For your own projects you can choose any coverage area you'd like.

If you need to place an hydro poly exclude make it as small as possible (it does not need to cover your complete area of interest as it excludes the entire polygon it intersects anyway), then check in the sim what particular cells have been turned to land, then cover those with your replacement hydro polys.

Cheers, Holger
 
#4
Thank you, gentlemen!!! Your professional tips mean a lot to me... Another dogma swept away. :)

If I'm not mistaken, Holger, your statement compliments the following one from SDK:

The clip levels are the defaults used by ESP data. Clip level 11 is QMID level 11. Setting higher clip levels will create more detailed data, but at the expense of size and performance.
which basically means that the developers are not limited to the default clip level specified under <Geometry> element of the XML file (clipLevel="11").

Thanks!
 

rhumbaflappy

Moderator
Staff member
Resource contributor
#5
which basically means that the developers are not limited to the default clip level specified under <Geometry> element of the XML file (clipLevel="11")
Resample will compile the higher clip levels, but FSX ( or Flight, or P3D, or FSW ) might not display them
 

rhumbaflappy

Moderator
Staff member
Resource contributor
#6
QMID 7 sized BGLs were a matter of convenience to the Aces, I believe. It gives a welcomed organization to the vector and mesh files.
 

HolgerSandmann

Resource contributor
#7
Hi Rustam,

I haven't experimented with the clipLevel parameter in the xml file but often clip polygons and vectors to higher QMID levels within SBuilderX or other GIS tools prior to compilation with Shp2Vec.exe. In fact, if you have polygons with complex shapes (in particular concave geometry) then it's advisable to simplify those polys via clipping because Shapefiles are somewhat notorious for causing display problems when they are very complex. For example, if you have a landclass polygon wrapping itself around another polygon on more than two sides one often sees an odd peeling-off effect moving along with the user aircraft; several default airports show this problem, such as FNLU (Rwy 07).

Cheers, Holger
 
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