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FSXA LOD mystery

JohnC1

JohnC1

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I don't have the complete story on LOD's.

In the process of porting all my stuff from old to a new computer, I found some of the LOD techniques unreliable the way I was implementing it. To check out why, here is what I did.....

I created 3 equal five foot high edittable mesh cubes separately in gmax...no cloning.

I renamed Box01 to QQQ_LOD_50,
Box02 to RRR_LOD_100,
BOX03 TO SSS_LOD_150.


I put 3 very large white non-LOD boxes visible from a very long distance (called AAA,CCC,and LLL) close by 50 feet or so.

There is nothing else in the scene so these 6 boxes ARE THE ONLY OBJECTS IN THE MDL I get when I export it/compile it to a BGL.

They are positioned left to right in the middle of a flattened airport..

When I fly or slew toward the boxes from a long distance away where the 5 foot boxes would be a few pixels at most, I would expect the LHS box to pop into view at some point, followed by the center then the RHS box.

I would expect the large white boxes to appear ALL THE TIME.

Doesn't happen that way.

They pop up alright, (a) QQQ_LOD_50 first, but ------------------->(b) NO large white non-LOD boxes.
When RRR_LOD_100 pops up, (a) QQQ_LOD_50 DISAPPEARS and ---------->(b) the large white boxes pop into view.
When SSS_LOD_150 pops up, (a) RRR_LOD_100 ALSO DISAPPEARS,and----->(b) YES, the large white boxes NOW disappear.

Changing QQQ_LOD_50 to QQQ_LOD_050 made no difference.

Putting the BGL's in a separate scenery and unchecking every other addon made no difference.
I'm reluctant to make any more moves to optimize my many scenery objects until I figure out what I am doing wrong. Till now, I haven't got any reliable results.
Can I get some comments/suggestions?
"this is an easy scene to replicate and see for yourself".:D
 
JohnC1 said:

Till now, I haven't got any reliable results.
Click to expand...

Actually, you have reliable results. What you are reporting is exactly the behaviour you would expect in FSX.

In FSX, you require a proper hierarchy for your LODed parts. On this basis, you have a root node with all the LOD parts anchored to that.

The other effect, is that only the root node and the relevant LOD are displayed at any given LOD level. The prefix part of the name is irrelevant (ie the QQQ bit)

The LOD_xxx or LOD_xx nomenclature is also equivalent, but makes it easier to sort in your parts list.

So unlike FS9, you need to have different iterations of each of your scene elements in each LOD. In other words, each LOD replaces the scene, rather than adding to it. This may seem cumbersome, but in some ways it is more flexible, as the rudimentary geometry is no longer displayed.

LOD switching is calculated based on:

diagonal dimension of bounding box as presented to the viewer (ie the entire scene)
dependent on zoom level, and monitor resolution.
 
What throws me off is the invisible white boxes with an LOD_50 object included with them, and their consequent appearance with an LOD_100..

I am going to have to go back and figure out what a root node is.

Thanks for responding and your patience.
 
Last edited:
Hi,

In FS you can't have part with and without a LOD in the same MDL. So that's why your white boxes appear at the same time as the highest LOD.

Also each LOD will replace the previous one. So that's why the LOD_50 disappears, when LOD_100 appears.
 
I'm getting somewhere....maybe...

Here's the mystery for me... if I understand Arno correctly

I can't have a part named XXX in the same MDL as XXX_LOD_NNN.

Or is it

I can't have any parts named YYY in the same MDL as any XXX_LOD_NNN.

But I don't...I have 6 separately created and separately named parts:

3 boxes with LOD's and three other boxes with no LOD.

Does that mean that all I have to do is put all the LOD parts in a separate MDL?

Furthermore, my white boxes don't disappear with the highest LOD appearance....they show up only at the middle value of LOD_100.

LOD_50 ... no boxes
LOD_100 ... boxes (Totally unrelated boxes to the three LOD boxes)
LOD_150 ... no boxes...........:eek:

I will try keeping LOD's separate in a companion MDL.

I have many light posts and lightning rods on my large hangar, and a very complex hangar door protection scheme.

Lots of stuff you shouldn't waste time on far away....
 
I'm not quite sure why this is complicated:

At LOD_50 all objects tagged with _LOD_50 or _LOD_050 will appear.

The same for each separate LOD specified.

Non tagged objects will default to a LOD_100

If there is no established hierarchy in the scene ( a root node and linking) then that is how it will behave.

SO:

At each LOD display level you need an ENTIRE version of your scene, as you want it to appear at that level of detail. It is not cumulative (different to FS9).

As I explained, the model name (apart from the LOD_xxx tag) has absolutely no bearing on what gets displayed.

You can have as many objects at each LOD ... but if you create (say) a single LOD_060 object that that is the ONLY object that will display at that switched level. The others will disappear.

If you wish to make it easy, you might have the following objects:

LOWDETAIL_LOD_050

LOWDETAIL_LOD_100
MedDETAIL_LOD_100

LOWDETAIL_LOD_200
MedDetail_LOD_200
HighDetail_LOD_200

In this example, you clone the LowDetail object into each LOD (50, 100, 200)
At each level extra detail is added.
 
So far so good.....

HC says........Non tagged objects will default to a LOD_100.....OK.

Jeez, I wish the PHD they hired to document the FSX SDK could have put that somewhere prominently in the SDK. :rolleyes:

That permits me to go back to work and put my disappearing white cubes out of mind.
 
BTW, FS9 works exactly the same way - each LOD model *replaces* the others.

Also, I have found the rule about not including non-LOD objects in an LOD containing object can be broken (at least in FS9) if the objects that are not LOD are light objects, like landing or taxi lights. These work fine and display at all LOD values.

Hope this helps,
 
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