P3D v2 Autogen Annotator produces buildings with incorrect orientations

[spatialpro]

I'm using Autogen Annotator to place default buildings (Roofs Gabled Row 1 and Roofs Gabled Row 2) on photoscenery. I draw the longest edge first and then expand the polygon to give depth, as usual. I very carefully align the orientation of these buildings with the photoscenery. However, in the sim their orientation is incorrect. It seems pretty consistently incorrect... I'm guessing ~5 degree clockwise. Has anyone else suffered from this? Does anyone else know of a solution?

 

[JRobinson]

Just a guess but does turning tessellation off in settings change anything? I've noticed some shift with tessellation on vs off, but not necessarily rotation. I'm interested to know the outcome.

 

[spatialpro]

Hmmm, I can't seem to switch off Tessellation using the menu and restarting (it seems to remain on)...

 

[JRobinson]

That's strange, are you all updated through v2.2 + the flight planner hotfix? I'm still running a v2.2 beta, maybe they changed something so you can't turn it off? (I have a big project going and don't want to risk messing something up by installing updates ATM) Maybe try switching it off in the Prepar3D.CFG, try:

[GRAPHICS]
TESSELLATION=0

Jim

 

[spatialpro]

OK, I switched Tessellation off using:

[GRAPHICS]
TESSELLATION=0

However, it didn't change the orientation of the autogen buildings.

I have a suspicion the Annotator, or the sim, might snap each building to the nearest N degrees (e.g. 5 degrees)...

 

[HolgerSandmann]

Hi there,

another reason for the misplacement could be the latitude-dependent distortion inherent to FSX and P3D: the higher the latitude (above ~40 degrees) the larger the distortion in the ground textures, landclass or photoreal. In contrast, the texture files or images loaded into Annotator aren't distorted in the same manner. You can cross-check by taking screenshots of Annotator vs the sim (top-down) comparing distances and angles.

Probably the easiest work-around is to figure out the approximate local offset and then compensate for that (blindly) in Annotator. That's what I did when annotating photoreal areas in Alaska.

Cheers, Holger

 

[arno]

Hi,

I think Holger is right here. When creating autogen with scenproc I have seen the same. In my geo data the buildings align perfectly and also in annotator. But in fsx there is a few degrees heading offset. This must be due to the way that fsx handles the distortion.

For scenproc I hope to add an automatic correction one day. When I find some time to check the math behind it

 

[HolgerSandmann]

Hi Arno,

I don't know the specifics either but Joachim Buhre figured out for FS9 (famously with the use of Ernie's head from Sesame Street!) that the latitude of no distortion is at ~42 degrees with raster grid X-dimensions getting narrower towards the pole and wider towards the equator. That may be different in FSX due to the changes implemented to its world geometry though the effect does appear to be very similar.

The link to the PDF version of Joachim's "Landclass Terrain Doku" is still active though the document is available in German only: http://www.germany-vfr.de/Jobia/lcdokupdf/lcdokupdf.zip ; Ernie's face is featured on p46-50

Cheers, Holger

 

[arno]

Hi Holger,

Gues I should practise my german a bit more

The autogen tiles have a ratio of 4 by 3 in degrees. So that indeed means that at latitude 41.41 they are completely square in metres as well. That's a simple acos calculation.

So I guess it shouldn't be too hard to compensate for that distortion. I'll try to experiment a bit with it.

 

[arno]

Hi,

This is actually an interesting topic, the more I look into it, the more interesting it is

I made a small test photo scenery in northern Norway, as the distortion is bigger there. Attached is a screenshot with a view with two buildings in Annotator and FSX. In Annotator I carefully aligned the buildings with one of the edges in the photo. As you can see in Annotator already the other edge of the building is not aligned with the photo at all. That's due to the distortion already (the image is distorted since it's displayed in degrees, not in meters).

As you can see the buildings in FSX are no longer aligned with the edge that I drew them along. But if you would like to rotate the building a bit to compensate for the distortion seen in Annotator, I would actually expect it to be rotated in the other direction.

I also tried to calculate what kind of offset I would expect and the actual values I see in FSX for the offset are bigger than that. I almost have the impression that MS might have tried to compensate for the distortion, but that they got a minus sign wrong somewhere. So that in the end they ended up with a twice as big distortion.

I'll try to do some more testing tomorrow to see if that hypothesis is actually true...

 

[HolgerSandmann]

Hi Arno,

interesting indeed. From your screenshots it's obvious that the distortion is the other way around than what I mentioned above namely right angles are distorted in Annotator while they are more or less correct in FSX. That reminded me that Joachim actually points out (p.50) that the issue with the distortion in the sim is primarily with landclass ground textures since photoreal imagery compiled with resample.exe uses degrees as pixel dimensions and is, of course, location specific. In contrast landclass ground textures are just "arbitrary" texture sheets and often based on source imagery in UTM projection. Moreover, they can be placed anywhere in the world and thus compensation for latitude-specific distortion is pretty much impossible unless texture sets are created (and annotated) for specific latitude bands.

In short there are two separate issues here: photoreal .bgl files are being distorted in Annotator and landclass ground textures are being distorted in the sim; only the former seems something we can practically compensate for.

Cheers, Holger

 

[arno]

Hi Holger,

Yes of course. Landclass has a different issue since it can be used at any latitude. So an image that looks ok at latitude 40, will be distorted near the poles. Nothing to be done about that.

I wonder what the Landclass autogeen then does

 

[arno]

Hi,

I did a little more testing tonight. I did rotate my autogen buildings with an extra angle to correct the distortion. As you can see in the attached image it looks like garbage in Annotator now, but in FSX the orientation is much better.

There is a position offset now, I already expected the orientation would result in that. But I think I can compensate for it.

And to make it better I could also take into account that after rotating the object, the heading is different and therefore the distortion angle as well. So I might be overcompensating a bit now. Objects that have a heading of around 45 degrees are affected most.

I need to do a bit more testing to see if this really works on any place in the world, I only tested it in northern Norway for now. I only had to apply my offset angle once, so I don't think MS did a wrong correction, it seems they just didn't add a correction at all.

 

[arno]

Hi,

I have now rotated the buildings around their center, instead of around the corner point. That seems to have fixed the positional offset and the orientation looks quite good as well.

I have done some testing in the Netherlands as well now and it seems to work out quite OK. I guess I should test near the equator or in the southern hemisphere as well. But I think I understand the distortion now.

Only other issue is that I have now learned that the distortion messes up my code that I use to split a long and narrow footprint into multiple buildings. So guess I need to look at that as well

 

[HolgerSandmann]

Hi Arno,

very nice work! It's quite amazing how so many years after the original release of FSX we still get to come up with new solutions to tweaking rather fundamental aspects of the display engine ;-)

Cheers, Holger

 

[L_Rob]

Guys, I'm not sure if this is directly related, but I find that even at ~48 deg lat. my quite large scenery objects like ferry terminals built based on importing a Google Earth geo-location in Sketchup need to be rotated a couple of tenths of a degree based on size in order to line up with the FSX/P3D terrain at sea level. Is this the same issue?

 

[arno]

Hi Rob,

Are you placing them as autogen? Because this only seems to affect autogen buildings.

What you might see there is the convergence angle between different projections. Fsx uses geocentric coordinates and I think sketchup uses a kind of flat earth or utm like projection. That's something different from this issue.

 

[arno]

Hi,

I did a little more testing. I had been testing the autogen buildings only until now, but the rowhouses and library objects placed with Annotator get the same offset. The polygonal buildings are not affected.

 

[arno]

Hi,

I have put the correction into scenProc now. And I have tried to explain how the distortion works in this blog post:

http://www.scenerydesign.org/2014/05/autogen-object-distortion/

 

[Wills]

Great work integrating the automated correction into Scenproc Arno - Looks great!

I'm working on a scenery which I don't have GIS data for so am planning to annotate by hand. Is the SDKs annotator tool still the best (or only?) way to do this? It'd be great if I can use Scenproc or another tool to annotate which will automatically correct for the autogen rotation/translation?