Question

FBX reader units & coordinate system *-1

  • 20 December 2022
  • 5 replies
  • 13 views
T

I have brought in an FBX as I need to carry out some coordinate transformations to it as part of our workflows.

 

This is the fbx model in navisworks, units in metres, modelled in EPSG:27700:

Capture 

The model is orientated north, and the top left point is (330213.690, 376187.218, -2.7)

 

When bringing this into FME, the coordinates are multiplied by -1:

imageThe same point within FME's data inspector is (-330213.6044, -376187.4125), which is equal (ish) to the above point, but multiplied by -1. The orientation is incorrect but this will be due to the coordinates being multiplied by -1.

 

Is there a reason FME has inversed the coordinates when reading the FBX? Is this typical for reading FBX files?

 

Also - what transformers would be required to make the coordinates positive / *-1 for each xy? Not z, it looks like the z coordinate has the correct sign.

 

Thanks for your time,

Tom

 

 

 

 

 

 

 

5 replies

T

FYI I just used the 3DRotator transformer, rotated 180 degrees around the Z Axis and it sits in the correct position in EPSG:27700. Although I am still unsure as to why FME negates the coordinates. Any more info on this is appreciated

T

Any updates on why this is happening?

natalieatsafe
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Badge +6

@tom_james​ Hi Tom, thanks for your question. I've done a bit of digging into the FBX format, and I suspect the behavior you're seeing is due to how FME orients FBX scenes before reading them. By default, the FBX reader will convert the scene before reading it, such that it is oriented with Y-axis up, Z-axis out toward the viewer, and X-axis to the right. Would this re-orientation have possibly moved your Y-axis and X-axis by 180 degrees?

T

Thanks @natalieatsafe​ , to my understanding, if the axis are swapped the coordinates should stay the same, but the xyz coordinates of each vertex would be swapped to suit. This might mean that the orientation is changed locally for each vertex, but not around 0,0,0. (The model would be on it's side for example, but still be in the correct location).

I've also seen that this happens with the Revit reader from this thread: https://community.safe.com/s/bridea/a0r4Q00000HbqWtQAJ/revit-reader-upgrades-for-reading-coordinate-systems

 

We can see that the Z Axis is out towards the user in both autodesk Navisworks and the FME inspector - the X and Y coordinates have just been negated for some reason.

 

 

natalieatsafe
Rank
Badge +6

@tom_james​ I reached out to a couple colleagues who have more hands-on experience with the FBX format than I do, and they're suggesting a similar thing to what our FBX documentation describes with the FBX reader reorientatiing scenes to be right-handed. However, that doesn't mean there isn't something odd or unexpected going on in this case. I think there would be much value in taking a deeper look at the behavior you're seeing, just to check on our FBX format and see if there is anything unusual going on during a read-in. Would you be able to submit a support case to us, with a sample of your FBX data, a copy of your workspace, and your FME version and build number? You can submit a support case request to us here.

 

Just as a side-note, I also noticed in our FBX documentation that our FBX format does not have full coordinate system support. This fact may also be playing into this issue, but investigating further will help figure that out, too.

Please let me know if you need any assistance in submitting a support case, I'd be happy to help!

 

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