Different LODs within one BGL using Resample.

[RicherSims]

Hi guys. I've been trying to optimize my photoscenery and I'm wondering if it is possible to place multiple LODs within one BGL, instead of using different BGLs, each with a higher resolution.

I know that resample will automatically choose the best LOD according to the resolution of your data, but I believe this is one maximum LOD, no matter the sources.
I am wondering if it is possible to tell resample to use LOD 16 for one source, LOD 17 for another source and LOD 19 for another source, where the LOD 19 image covers a small area within the LOD 17 image, and the LOD 17 image covers an area within the LOD 16 image. (See image for further clarification).
Can these all be placed within one BGL?

The reason I'm asking is because I'm seeing some issues where overlapping BGL areas cause conflict. Usually FSX would display the one with higher resolution on top, but this is not always the case.

 

[rhumbaflappy]

By default, resample for FSX will have multiple LODs.

Dick

 

[RicherSims]

Thank you for the response Rhumbaflappy. I am aware of that, but it does not really answer my question.

Let me rephrase.

How would one set up an INF so that ONE BGL will display, for example, up to 0.6m/px in one area and up to 0.15m/px in another?
...If it is possible, of course...

 

[arno]

Hi,

I don't think that is possible. The maximum lod is the same for the entire bgl as far as I know.

 

[LCSims]

I don't know about photo based work, but mesh files are capable of holding different maximum LOD values. Check a North American default mesh file and you will see Canada stop rendering in TMFviewer, while the US portion shows at a higher LOD value.

 

[arno]

Maybe it works if you have multiple sources each with a different resolution. I am not sure what the lod = auto value would do in that case.

But the lod value is set for the output, not per source, so if the sources have the same resolution I don't think it's possible.

 

[RicherSims]

It was as I feared. Thank you for the confirmation.
LOD=Auto sets the output for all sources to match the LOD of the highest resolution source.

Can be quite a long wait when you mix a large area of 1.2m/px with a small area of 0.15m/px!

 

[GaryGB]

Hello:

I have seen a few FSX scenery packages with up to 3 separate aerial imagery BGLs, ex: 1 BGL for each resolution of "source data" per area.


However, I'm not certain whether there is a performance benefit to implementing one's aerial imagery data in separate BGLs when used in FSX.

IIUC, there may actually be a performance detriment to implementing one's aerial imagery data in separate BGLs:

http://msdn.microsoft.com/en-us/library/cc707102.aspx#PerformanceTipsforAerialImagery

[EDITED]

NOTE: The SDK docs do not specify just how many aerial imagery BGLs ...constitutes "a large number" !


AFAIK, when aerial imagery BGLs (and I would presume, terrain mesh BGLs also) are read, they are incremental reads from sections of the file which are pertinent geographically, and by LOD (as a function of aircraft visual display radius 'distance' in X,Y,Z directions or a combination thereof ...from the NW corner of a terrain quad tile within the FS quad matrix grid).


Thus, rather than the entire imagery / terrain mesh file being read and re-read at run time (even though up to a 2 GB file size is allowed, usually less than 500 MB - 750 MB max Resample output BGL file sizes are seen used in most add-on scenery packages), only portions of the (virtualized ?) file are being read to minimize the performance hit FSX incurs from file I/O.

[END_EDIT]

Hope this helps !

GaryGB

 

[toprob]

The reason I'm asking is because I'm seeing some issues where overlapping BGL areas cause conflict. Usually FSX would display the one with higher resolution on top, but this is not always the case.

Given that it looks like you can't mix LODs in one file, it is possible to get overlapping BGLs to work. Just use auto LOD for both (for min at least). Then alpha-sort the filenames, as this makes a difference. Higher LODs need to be loaded first.

 

[RicherSims]

...it is possible to get overlapping BGLs to work. Just use auto LOD for both (for min at least). Then alpha-sort the filenames, as this makes a difference. Higher LODs need to be loaded first.

I did not know that! That may solve all my problems! Thank you!

Gary thank you for the additional info, but that performance cost may be a small but necessary evil.

 

[benclark]

Maybe it works if you have multiple sources each with a different resolution. I am not sure what the lod = auto value would do in that case.

But the lod value is set for the output, not per source, so if the sources have the same resolution I don't think it's possible.

Interesting so if I set have save 5 source inf files with LOD 11-15 boundaries for example (but all calling the same high resolution data file) and a single destination inf file with LOD=Auto, I won't end up with a combined LOD 11-15 BGL file but instead just a LOD 15 BGL file that's taken me 5 times longer to make? Would I need to decimate my mesh down to each LOD level and have 5 source files, one for each source inf file? I hope not, that would be days of work in the end and would make single LOD BGL files make more sense.

Edit - I reread the FSX SDK and realised that setting the inf file up with "LOD = 10,15" in the Destination section would create that multi-LOD terrain mesh BGL file during which I also realised that you don't need different boundaries for each LOD as being powers of each other they ultimately share boundaries at some point so now I have a multi-LOD BGL file that worked out to be 1.5 times the size but now with the default scenery has every LOD level covered all the way down to an oversampled (2m source data) LOD15. Needless to say pretty happy right now as this is going to save me hour upon hour of work that I thought I would be facing!

 

[Armintrude]

Bit of an old thread this but it's one of the few I've found covering an issue I've had trying to get sources with different LOD's in a single BGL. I discovered that in order to get the different LODs to display at max resolution, only for the area covered by that source, you simply need to order the sources in descending order of LOD within the inf, i.e. highest LODs at the top, lowest at the bottom. The LOD output can be set at AUTO.

The resulting BGL shows a LOD range up to the maximum source LOD used with the higher LODs only covering the areas defined by the sources. In fact if you use tmfViewer and set it to display the highest LOD used only those source area are displayed. It's also obvious from the time it takes to compile the BGL and its size that it isn't using the max LOD for the whole BGL output just the discrete areas covered by the sources.

If you don't order the LODs correctly in the inf then the higher res LOD sources seem to get "smothered" by any lower res LOD source defined above them in the inf file with the resulting BGL showing the lower LOD as the maximum for the BGL. You'd think resample could order the sources itself but it doesn't seem to.

So it does appear you can have multiple LODs in a single BGL and have them display at the correct LOD level ... except, and this is the problem I have, you get default scenery showing up momentarily as you fly over the boundary between different LOD levels. It appears in blocks along the boundary and disappears again as you fly away. I've read somewhere this is down to a conflict between different LODs within the same BGL. Also read something about Default scenery and LOD 13 issues, but this problem still happens between boundaries higher than LOD 13 so don't think that's the cause. Really trying to find out if there's any solution to this problem ?

I resorted in the end to just putting the same level LOD sources in single BGLs and alphanumerically sorting them in the scenery folder to get them to display correctly, as mentioned above. This in fact works fine and probably has some advantages anyway, such as being able to use blend masks at the edges, something you don't seem to be able to do with a multi LOD BGL (just shows the default scenery where the Blend mask is rather than the underlying lower res source). Disadvantage is you potentially end up with more BGLs.

So, is there any fiddle to get around this conflicting LOD boundary problem in a multi LOD BGL is the question ?