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BGL -> AC: inverted axes and other problems

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italy
Hello, thanks for the fast approval!

I downloaded a few days ago the development version of MCX. I'm trying to improve a bit my area in FlightGear and it was a great find! The batch converter is a precious thing and I'm experimenting with it.

However I'm having a couple of problems. One is with axes, I've read about that on the blog. I had a hard time figuring out, but Y and Z seem to be inverted in AC3D (at least the vertical one), although in FG they're fine. Almost. That is, they're not upside down, but they're on a perpendicular direction (I haven't tested a lot, I rely on your experience to fill the gaps).

If I flip things so that they're correct in AC3D, they're messed up in FG. That is, direction is correct, but they're twisted inside out and upside down.

Note that models designed in AC3D look the same as in FG.

Here's an FSX model I used (comes from here). There are three models inside Ancona1/Cattedrale Ancona FSX/scenery/AnconaLib.bgl. Two of them, apart from the flipped axes, look ok. The other, Cattedrale16.ac, seems to have issues with textures. In AC3D it's all black, but I can see the alpha shape of the trees, so the texture is loaded. In FG it's invisible.

One last thing. One of the models I used is scaled up by x10, so I needed to apply 0.1 to the "scale" operator, but it only accepts integers.

If you need more tests let me know!
 

arno

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Hi,

In the options there is a setting for the up axis you want to use (y or z). I think if you change that it should export them differently.

Where are you scaling? In the scale object form you can type any value.
 
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5
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italy
Hi,

In the options there is a setting for the up axis you want to use (y or z). I think if you change that it should export them differently.

Where are you scaling? In the scale object form you can type any value.
Hello,
I just tried to change that option, both doing a single import/export, and using the batch converter. It makes no difference. However, to be clear, the problem is not that Y and Z are one in place of the other. The problem is that Y and Z in AC3D have both the wrong sign... and that flipping them in AC3D fixes the problem in AC3D, but makes them messed (in a worse way) in FG. Things are a bit involved and I find it hard to explain the situation.

Basically however the problem is that an object looks in a way in MCX, then I convert it and it appears in a different way in AC3D, and in one more in FG, when they should all look the same. Editing then becomes quite painful. Moving vertices has not the same effect as moving the whole object, or the whole group, so as I need to split every building/vehicle/furniture*, it goes with a lot of trial and error and redo from scratch.

(I don't know if this is normal for what I'm doing or if this is a limitation of AC3D, or just the fact that I lack the experience - and confidence with linear algebra. I'm almost done, but if I knew earlier what I was going to face I'd have given up.)

Regarding the scaling, I'm referring to the "scale" operator in the batch converter (sorry, actually it's a lot of objects I need to scale, not just one).

* FG scenery can change elevation data, and airports are sloped, so objects must be split and not assume they're all on the same flat level.
 

arno

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Hi,

Those different axes systems can be annoying. ModelConverterX uses a right handed axes system where z is up. Fs uses a left handed axes system where y is up.

Do you know what FG expects? Then I can check if the export is correct now.

Why it's different in ac3d again I don't know.

Let me check the scale in the batch operator, but it should be a double.
 
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italy
I'm back with an experiment. I created a cube, textured its faces with AC3d axes directions and spawned it into FG. I did that in a couple random places to be sure.

+X points SOUTH
+Y points UP
+Z points WEST

As of the difference in AC3D and FG, I think they have a different interpretation of relative coordinates, when a group/subgroup/object has a "loc" line set. In fact, if from "hierarchy view" I move an object out of a displaced group, in AC3D it stays where it is even after reloading the file, in FG its positions become relative to the new parent. (which is quite weird, because I couldn't find how AC3D, or FG, remember the old position)
 

arno

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Hi,

Interesting. I think fs uses x as east, y as up and z as north. So there seems to be a difference indeed. I probably export to ac3d with the wrong axes.
 

arno

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Hi,

Sorry I forgot to look further into this. I should add it to my bug list.
 

arno

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Hi,

I feel a bit ashamed to bump this old thread, but I happened to run into this thread today and I have just fixed this issue (I hope). The axes used should be aligned with FlightGear now. Sorry for the looooong delay :)
 
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