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Troubled coordination...

hek293

hek293

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Here is the problem:

-I export a runway from GMAX with the FS2002SDK MakeBGL using coordinates.

-I export the same runway as .MDL from GMAX (FSXSDK), which I then place through BGL compiler (FSXSDK), using the exact same coordinates in my .XML file.

Why are these two runways not completely aligned ?

…there seems to be an offset of 5-10 meters, possibly some rotation as well by 0.5-1 degrees..

Any ideas?

Thanks
Emilios
 
It may depend on the heading ... but Makemdl2002 does not accept fractional degrees (decimals), only whole units ... so they may be rounded.
 
in fact, the runways are exported with 0 heading. instead they have a heading in gmax.

so essentially the same model gets exported with 0 heading from either MDL2002 of FSXSDK BGL compiler at the same coordinates, and they are coming out slightly mis-aligned...:confused:
 
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Emilios,

I have noticed this problem recently too, but have not had time yet to investigate. My first suspicion is that it is related to the object being very long - a runway in your case and a very long, straight taxi line in my scenery.

Have you tried dividing the runway plane into 100-meter segments, as required by FSX? That would be my first step, along with centering the pivot for each segment.

Do let us know if you find a solution!

Z.
 
Hi,

FS2002 style ground polygons are "corrected" for the curve of the earth. This might give a small offset compared to a MDL object. But I would not expect that to be 5 or 10 meters.

How long is your runway?

Also be aware that your MDL runway will probably be floating, because it is not adjusted for the curve of the earth. So that might seem to give a visual offset as well.
 
Hi Arno,

May be less than 5-10 meters off :) but is still visible even when set to ground level. Nevertheless what you said about earth curvation makes absolute sense. The FS2002 runway is indeed segmented evey 100m or so.

The runway is about 2200 meters, is this enough you think to produce this difference ? If this is the case there might be no cure, at least not an easy one no?
 
As a test - what about detaching one of the 100-meter segments as a separate object, recentering the pivot, reset transform/scale and exporting?
 
Hi,

Did you try in top down view as well? If the MDL runway is indeed floating the offset you see might be mainly due to the elevation difference, not because the actual placement is that much wrong.

Is the reference point in the middle of the runway, that should also minimize the effects?
 
Top down was also the same as I set the MDL at ground level.

BUT, solution found.

My conclusion was that the .MDL, compared to FS2002 .BGL runway, is off by:

Heading: 0.02 degrees

and by scale (!?!)

by : 0.001 (so actual MDL runway scale must be 0.999)

Kinda weird no?
 
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Perhaps this has something to do with the difference between arc-length and chord-length for a curved object.

Interesting observation though.
 
Over the last days I have been working on the calculations needed to make ground polygons that are in different reference point line up again. The formulas we always used in FS2004 to calculate the XY coordinates no longer work with the updated earth model in FSX.

But I am surprised to hear that the same model exported with both approaches already gives an offset.
 
although useful to know the offset values, the 'compile-->reload scenery-->compile-->reload scenery' cycle was rather nerve testing.

I wonder whether smaller polygons would align better with the FS2002 polys...

thanks for the stimulating discussiin, I woul probably still be looking at it thinking what the hell is wrong with it.... ;)
 
Hi,

I will try to repeat your experiment here today, it is interesting and I would like to see what is going on.
 
Hi,

I repeated your setup. I made a 3000 x 50 meter runway. I exported it both as a FS2002 BGL and as a FSX MDL file. Then I placed them at the same location.

I do not see any rotational offset. But if you look at the end of the runway you indeed see that the FSX MDL is floating above the ground a bit. The FS2002 BGL below is following the ground, but about 1 meter shorter. See the screenshot I attached.

I guess this difference can be explained from the new earth model, but I did not try to calculate that now.
 

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thanks for the image !

this reminds me of what I saw as well :D... probably the rotation offset in my case could have something to do with the geometry of the object..:confused:

so actually by tweaking the scale of the .MDL one can only create the 'illusion' that these two runways are aligned to each other, while they actually aren't.
 
I don't have experience with FS2k2 ground polys, but have seen problems with fsx generic buildings and fsx mdls are not correctly placed per the lat/lon in the placement bgl. Happens only at certain locations and have never seen it figured out where or why. I've had even a problem where the base mdl is not correct placed, but attached objects are resulting in the attached objects not actually being attached.

So I would put your aircraft over the origin/ref point of the model in the sim and read out the coords with something like tcalcx and compare to what is in the placement.

scott s.
.
 
Hi Scott,

That is not what I am seeing. The placement is fine. At both sides of the long polygon I see the same offset. I am quite sure it is caused by the round earth.
 
Hi Arno,
I think the runway making by gmax are almost the same by both methods. But we cannot measure it in FS world if the length of both methods are the same as what we do in gmax. I made a runway by using satellite photo and map to gmax plane. The length of runway is correct in gmax. But when I export to FS world, the runway length is increasing and does not match with photoscenery made by resample tool. How would we correct this? I can resize the runway a bit but it is a very tedious job. I have to export and look in FS, then correct the length again, back and forth so many times. Do we have anything or mathematic way to correct the length to match the round world in FSX.
Thanks for the answer.
Best Regards,
Tic
 
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