Flattens inactive (under specific circumstances)



Hi there,

Quite a number of users have reported issues with (sloped) flattens not working at Arlanda, but 90% of the times this only occurs when a flight of >1 hour has been flown to this airport.

To illustrate: this taxiway is "elevated" with tunnel objects placed in the ditches.

When the issue occurs the entire area is flat, and therefore there are obviously problems with the tunnels.

Any idea why this might be the case? I've tried having the flattens in seperate bgl's, or all as one, to no result.

After a one hour flight and you end up there where the screenshot is taken from? I am afraid you are going to have a problem getting down in one piece:).What happens if you just taxi that way? Does it still show up flat?
I guess you are overtaxing your processor/graphics card capabilities.
I do not think there are any problems with the tunnels at all.
I do not have Arlanda but I am sure that this is not due to their bungling up their flattens.
You remind me of someone that complained about an airport not showing up when he was 50 miles away.
Sorry for being a bit rude but what is the purpose of looking for an anomaly that in normal circumstances would not be there (because you would not be there)? Does it influence your flight experience? You are supposed to be a pilot and have no time to look around at that particular moment because you have to concentrate on your instruments, the runway, etc.
But maybe the guys that made Arlanda will answer too (unless they think it is nitpicking on stuff that does not matter at all).


Hi Roby,

You misunderstand my post completely :rolleyes:

If one spawns at the airport, everything is fine, the 1 hour figure is just ballpark, basically any longish flight there *could* result in this happening.

I asked here hoping to get some experienced advice, (maybe from GaryGB) seeing as I couldn't solve it...

PS. Read my signature, I made those flattens.
Well, it is not very difficult to make those flattens. But because they are tiny, it is normal that they do not show up when you are far away from them.
They would probably not show up either when you do not set your scenery sliders (mesh, etc.) to the complete right either.
If you made those flattens, then I do not see where you could have done anything wrong when and if they show up closer up (I made the ones for ESGGo_O).
I guess it is just some shortcoming in FSX and probably still is in P3D.
But let us wait for Gary to chime in:).


The problem is not the distance from them, it is if you come from a distance. You can be right next to them and they won't show. If you spawn at the airport they are fine even from miles away. If you come from a long flight, say from Berlin, it can happen that they never show.

Just to make that clear.
Nope, I do not have that problem (I tried it in FSX) but of course, you cannot compare Landvetter to Arlanda.
It does take a while for the scenery to settle and then it will show the ESGG elevation differences and the tunnel but only when you are closer up.
I only made a short flight from ESGP to ESGG though.
How did you make your flattens (not that I know of that many ways to make them)? They are sloped ones I guess?
Suppose I will have to ask my friend to check. He has Arlanda installed on P3Dv3.


Sloped flattens yes.

Whether it happens or not is not really the issue, about 20 customers have reported this, and I guess many more just haven't bothered to. We have this happening across all platforms.


Staff member
Resource contributor
This does seem like a problem with FSX rather than with your BGLs. If I were to play with anything, I might try to use a hex editor to increase the geographic bounds in the BGL headers, and see if I could force FSX to load and retain the flattens at a further distance. Maybe that would do it.

Without a hex editing session, you might try to make tiny flattens at more far-flung extents in the BGL to force a larger bounds.

I agree with Dick's suggestion as a possible work-around. :wizard:

Holger Sandmann has previously reported that the FSX rendering engine prefers to load terrain mesh BGLs with larger extents (and thereby lower LODs), treating them as though they have a greater "priority" ...if they are the 'first' terrain mesh BGL encountered which covers the departure airport area.

FS then subsequently fails to load local terrain mesh BGLs with smaller extents (and thereby higher LODs) as one's user aircraft moves into the destination airport Geographic display 'trigger' area.

AFAIK, Holger's solution was to make all his custom multi-LOD terrain mesh so that each of his local airport area BGL(s) would have Geographic-coverage 'extents' out to ex: at least as large as LOD-4, and as small as LOD-12 ...inside the same BGL files.

Sloped CVX vector flattens compiled via FS SDK SHP2VEC are typically created as "local" objects by virtue of their being made as contiguous Triangulated Irregular Network (aka "TIN") terrain surfaces, and do not AFAIK have "LODs" in the usual sense associated with a multi-LOD terrain mesh BGL otherwise compiled via FS SDK Resample.

While it is curious that when the user aircraft enters their local Geographic display 'trigger' area, they may not still load "independent" from the local terrain mesh BGLs (even if one sets FS GUI terrain mesh sliders at 100% complexity and 10 Meters or higher resolution to enable adequate terrain grid vertices for rendering the "geometry" of the sloped flattens ? :scratchch), Dick's work-around may be the best remedy. :)

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FYI: Approximate FS terrain grid sizes in Meters for Quads and Area Points are summarized in a table here:


Thus the extent size of a LOD-4 quad would be a distance of 626,179.2 Meters (626.1792 Kilometers -or- 0.338013 Nautical Miles). :pushpin:

IIUC, following Dick's suggestion above, one might try placing a small 3-sided CVX flatten polygon (with an assigned Altitude of "-9999" to make it terrain mesh-clinging so it does not disrupt any other scenery at the remote location); that remote polygon should be 626.1792 Kilometers away from the ARP, but inside the same CVX vector "sloped flatten" polygon BGL for your airport project cited above ? :scratchch

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Gary and Dick,

I've done as suggested and have not (yet) been able to recreate the problem.

Your insight never fails :wave:
Hi Spitz:

Glad things appear to be working as desired.

However, I must properly acknowledge having posted a suggested work-flow based on as yet incomplete personal testing of an 'assumption' that the FSX SDK SHP2VEC CVX vector scenery compiler had the same capabilities as the FS2004 SDK compiler for LWM / VTP vector scenery ...which would otherwise have allowed use of the "-9999" value for Altitude of vertices in your remote 3-sided polygon intended to expand the Geographic coverage 'extents' in the header of the CVX vector BGL in question. :duck:

According to Richard Ludowise (aka "rhumbaflappy"), the ability to use what is referred to as a "NoData fallback value" to force vector objects to use the local FS terrain mesh elevation values as a 'mesh-clinging' object was not retained by ACES when SHP2VEC was developed for FSX et seq., as recently clarified and discussed here:


Sorry for any inconvenience this may have caused, but you may wish to slew to the location of the above cited "remote 3-sided polygon" in ADE or SBuilderX and edit the source code for the object to manually set an assigned local Altitude value (captured as AGL from the user aircraft position aligned upon the ground over that polygon's vertices ...as also discussed in the thread cited immediately above) so that it is compatible with the local terrain mesh; then re-compile the BGL to prevent any 'visible' anomaly in the ground surface displayed in FS at run time. ;)

Hope things otherwise are working well with your project ! :)

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