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Crash Boxes

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gadgets

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I want to put crash boxes around small items like lamp standards. From experimentation, it appears that neither FS9 nor FSX will detect a crash box with an area smaller than about 50 sq.ft. (1.5 sq.m.). Height seems to make no difference.

There doesn't appear to be anything related to this situation in either fs9.cfg or fsx.cfg. Does anyone know how to get around this limitation?

Don
 
gadgets said:
I want to put crash boxes around small items like lamp standards. From experimentation, it appears that neither FS9 nor FSX will detect a crash box with an area smaller than about 50 sq.ft. (1.5 sq.m.). Height seems to make no difference.

There doesn't appear to be anything related to this situation in either fs9.cfg or fsx.cfg. Does anyone know how to get around this limitation?

Don
Click to expand...

Don,

You probably already know that you can *disable* crash detection in a 3D object using some hacks to the mdl file and of course in FSX you can specify no-crash zones with Material properties...However, I don't know if you can override the bounding behavior as you desire.

I think you should ask this question in the 3D objects forum or somewhere like that, as those guys might see the thread and know the answer.
 
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Thanks for the suggestion, Mace. I've done it.

Incidentally, with FSX, you can also specify <NoCrash/> in the Scenery Object XML.

Don
 
Don,

this is for FS9 maybe this is an option in FSX too.

In FS9 you can in the sim the *Crash Detection* set Off.
Maybe you set it Off?
 
No, crash detection in the simulator is on. Basically, a box with a 8' x 8' footprint causes a crash but one with a 6' x 6' footprint doesn't. Likwewise, a 10' x 6' footprint crashes but a 10' x 3' won't.

Don
 
Hi Don,

Moved the question to the right forum (to prevent parallel discussions).

I would have to do some research but I think it can be because the crash detection is basically set up by dividing the bounding box of your object in smaller boxes and then saying for each of these boxes if it should crash or not. I can imagine that if they have a minimum size for those sub-boxes for small objects that could result in no crash detection. But to be sure I would have to check how this process is done.
 
Thanks, Arno. I'll appreciate any insight you can give.

Due to the problematic crash-boxes saved in the .mdl file for complex objects, I've disabled the crash boxes for my non-rectangular buildings and, instead, am planning on placing individual rectangular boxes - with a totally transparent texture where necessary - to create accurate crash-boxes. Don't know about the transparent-texture-part yet, but I can bring the a/c right up to the edge of a complex building before crashing when crash-boxes are created this way. (It's a pain and it will have an FPS impact, but it seems to work - though my tests are hardly exhaustive at this point.)

Since posting, I've discovered that I can work around the minimum size situation by making every box 4' larger all round than the building-segment it's meant to represent and defining scrape points for the aircraft which are 4' inboard of the real "edges". This is not an appropriate general solution since it requires each user aircraft to be so "adjusted". But, for my special situation I'm working on, it just might "do the trick".

However, I'm still hopeful somone can come up with a better solution.

Don
 
Further to my earlier post, the fundamental problem appears to be that the way that FSX handles crash-boxes comprising only one octree (i.e., very small objects). The crash-box for an object will have more than on octree only if is at least 3m. (13.3') on one or more sides. It would appear, then, that crash-boxes are defined by a collection of 3m. cubes, limited by the bounding box for the object. With that kind of resolution, it's no wonder we can't get reasonable crash-boxes on complex objects.

With only one octree, FSX is inconsistent in determining whether or not a crash has occurred. For example, I found that with a 3' x 3' object, if I favored one side of the object, I got a crash about 90% of the time. If I hit the object "dead-on" or favored the other side, I seldom got a crash. At about 2' x 2', I was hardly able to get a crash at all no matter what I did. As the size of the object was made larger the results became more consistent.

So, for consistent results with both large and small objects, it appears I have no alternative but to oversize the crashboxes and "undersize" the scrape points as discussed in my previous post.

If anyone knows better, please jump in.

In order to help with this, I wrote a small VB.NET program to output the crash box and bounding box parametes for FSX models. It's attached for anyone who might find it useful.

Don
 
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Thanks Don, that is interesting. I remember that for FS2004 there was a tool to make the crash boxes more accurate. Maybe we can use something like that on the FSX MDL files as well. But I can't say that yet without studying the crash box code in the MDL a bit more.
 
I have a question.

Why do you like *Crash Boxes*.

I'm happy when I'm on the Airport and my plane do not have a *Crash*.

I don't understand the want of *Crash Boxes*.

I need a explanation, please. :)
 
Arno, for regular, rectangular objects, the crash-box as used by FSX is already very accurate, since the bounding box of the object is used to "trim" the 4m. square "crash cubes" (not 3m. as I said in my earlier post). However, if you visualize a T-shaped building, the bounding box encompasses the "hollow" areas on each side of the leg. In those areas, the crash box is defined solely by the outer edges of the "crash-cubes". Hence, errors of up to 4m. can be expected. So, it would seem that a better definition of the crash-box in those areas will requre a reduction in the size of the "crash-cubes" which, unfortunately, will consume FPSs. Certainly, the solution to my problem would require a very significant reduction in size - probably to the point of being impractical.

However, it's not clear that the current arrangement of the "crash-cubes" generated by the Gmax game pack faithfully reflects the actual shape of the object. For example, with my CYYJ terminal (which is very complex), crashes were (until I added the <NoCrash/> option) experienced much further away from the building.

There are 8 sequential-bytes in the crash-box section of the .mdl file which were set to x00080001 in every file I examined. I was unable to determine their purpose which, hopefully, includes cube resolution. (But I was focussed on very small objects.) Perhaps you'll have better luck.

The FS9 tool you are referring to was written by a user named "anatolij" who hasn't posted in a while. All the links I've found to that tool are invalid. So, I've e-mailed "anatolij". Hopefully, he'll "surface" this week. (At least the e-mail didn't "bounce".)

This thread contains most of the useful information on crashboxes available on FSDeveloper.

Hopefully we'll soon see a new version of MDL Tweaker that "tweaks" crash boxes.
Don
 
Why do you like *Crash Boxes*.
Click to expand...
Sandra, I can assure you I don't like crash-boxes. I'm finding them very frustrating at the moment. However, in real life, if you hit a light standard or a building with your wing (speaking of airplanes, of course), you probably want to know.

I need that kind of realism in a project I'm working on.

Don
 
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