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FSXA Ground Poly Alignment Issues

FrostySoftware

FrostySoftware

Messages
29
Country
england
Hello!

I am in the process of working on an airport and I've hit a bit of an issue with my ground polygons. It appears that a model exported from 3DS Max does not align correctly in Flight Simulator X, even with the correct lat/lon point and orientation (The poly has been traced from a satellite image).

I have tried exporting the model manually with the fs2002 SDK and also with ModelConverterX but I still get a misalignment in the simulator. An image of the issue is attached to this post.

Is there a way to get perfect alignment in Flight Simulator X without warping the mesh after I have traced it in 3DS Max?

Thanks in advance,
Steve
 

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Well, the aerial image isnt good resolution therefore it's blurry. So when you are drawing your lines of what you think is the runway/taxiway/apron edge...you are probably a few CMs away from it.

I had this problem, but I just started to draw lines rite on the edge of the blur which done the job perfectly.

Regards
 
darren s said:
Well, the aerial image isnt good resolution therefore it's blurry. So when you are drawing your lines of what you think is the runway/taxiway/apron edge...you are probably a few CMs away from it.

I had this problem, but I just started to draw lines rite on the edge of the blur which done the job perfectly.

Regards
Click to expand...

I used several higher resolution images at the same zoom level to trace the groundpoly, so blurred edges were not a problem.

Is it just a case of tracing a poly that is a few meters wider than the original imagery suggests?
 
FrostySoftware said:
I used several higher resolution images at the same zoom level to trace the groundpoly, so blurred edges were not a problem.

Is it just a case of tracing a poly that is a few meters wider than the original imagery suggests?
Click to expand...

Negative, cause that would result in an un-accurate scenery.

You are using 3ds max 9 so take advantage of the "Render" tool

You just need to trace it exactley on the outer edge of the blur
 
darren s said:
Negative, cause that would result in an un-accurate scenery.

You are using 3ds max 9 so take advantage of the "Render" tool

You just need to trace it exactley on the outer edge of the blur
Click to expand...

I don't think the accuracy is the issue, I didn't trace the polys from the image shown in the screenshot above, I used several much higher resolution images and worked my way across the apron, it's a very accurate polygon of the apron.
 
Hi,

My first question would be how do you know for sure that the image is aligned properly in 3DS?

Another issue that might be involved is that ground polygons get corrected for the curved earth in FSX. This can give some offsets the further you get from the reference point. To prevent such issues you need to adjust it for the curve yourself (like the ground polygon wizard of ModelConverterX does).
 
Hi Arno,
I have used Model converterX (the new version) and tried it for ground poly. I think the results are the same as conventional method of FS2002. May be I did something wrong.
Regards,
Tic
 
arno said:
Hi,

My first question would be how do you know for sure that the image is aligned properly in 3DS?

Another issue that might be involved is that ground polygons get corrected for the curved earth in FSX. This can give some offsets the further you get from the reference point. To prevent such issues you need to adjust it for the curve yourself (like the ground polygon wizard of ModelConverterX does).
Click to expand...

The point 0,0 in 3DS is a sharp corner where I can get a precise latitude/longitude for, so I know that anything around that point will be aligned correctly.

Is the solution to a problem like this to split the groundpoly up into smaller sections and export them with their own reference points?

jtanabodee said:
Hi Arno,
I have used Model converterX (the new version) and tried it for ground poly. I think the results are the same as conventional method of FS2002. May be I did something wrong.
Regards,
Tic
Click to expand...

This is exactly the results I get, the groundpoly does not alter in alignment or position at all when exported manually vs with ModelConverterX.
 
FrostySoftware said:
The point 0,0 in 3DS is a sharp corner where I can get a precise latitude/longitude for, so I know that anything around that point will be aligned correctly.

Is the solution to a problem like this to split the groundpoly up into smaller sections and export them with their own reference points?
Click to expand...

I don't understand this. Even though you know the origin, having an image in WGS84 lat/long versus UTM projection will give you different results and thus a different alignment. You would need to have a local flat earth projection while working in a tool like 3DS to get perfect alignment with a resample photo scenery in FS.
 
How is the image scaled into 3DS Max?

I have not encountered the sorts of errors discussed above.

Manually measuring edgelengths for template and placing as FSX native ... (granted for a runway of only 2000m)

This is using a vertical ONLY deformation of vertices, to conform to Earth curvature, no arc/chord length adjustments.

The assumption being that if the imagery is ortho-rectified, then the lon/lat position should not require additional calculations.

Passage through MakeMdl 2002 perhaps introduces some other source of error (apart from the known hdg rounding)
 
arno said:
I don't understand this. Even though you know the origin, having an image in WGS84 lat/long versus UTM projection will give you different results and thus a different alignment. You would need to have a local flat earth projection while working in a tool like 3DS to get perfect alignment with a resample photo scenery in FS.
Click to expand...

So images obtained from Google/Bing servers are not suitable for use in 3DS? Where can I obtain 'local flat earth projection' imagery?
 
FrostySoftware said:
So images obtained from Google/Bing servers are not suitable for use in 3DS? Where can I obtain 'local flat earth projection' imagery?
Click to expand...

They are not really useful anyway, since you can not distribute any scenery that contains them. So they could only be used as reference for placing features.

But no, I would not directly use such imagery in a 3D modelling program. They use a different projection and that can give slight offsets.

How to get other imagery is hard to tell, that differs per country. For the projects I have worked on, I have always use GeoTIFF files of the region I am working on. These usually come from GIS suppliers, but finding them for free can be hard in some countries (the US has a lot of data available that you can use).
 
arno said:
They are not really useful anyway, since you can not distribute any scenery that contains them. So they could only be used as reference for placing features.

But no, I would not directly use such imagery in a 3D modelling program. They use a different projection and that can give slight offsets.

How to get other imagery is hard to tell, that differs per country. For the projects I have worked on, I have always use GeoTIFF files of the region I am working on. These usually come from GIS suppliers, but finding them for free can be hard in some countries (the US has a lot of data available that you can use).
Click to expand...

Ok, thanks for the help :)
 
arno said:
Even though you know the origin, having an image in WGS84 lat/long versus UTM projection will give you different results and thus a different alignment. You would need to have a local flat earth projection while working in a tool like 3DS to get perfect alignment with a resample photo scenery in FS.
Click to expand...

What is local flat earth projection? How would I go about reprojecting a GeoTIFF into it? Is there an option I can use in FWTools/gdalwarp?
 
Hi,

Sorry, I think I created some extra confusion with my last post :). I had forgotten that the flat earth coordinates FS2004 uses only depend on the cosine of the reference latitude, not of the actual latitude.

So to say it simply, an image in WGS84 projection will be a rectangle in the flat earth coordinates as well. All you need to do is calculate the XY position of the corners. Then you can add the image onto a plane as a reference while modelling.
 
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