.obj Export: NURBS curves exported with reverse orientation #72326

New Issue

Christian Hafner · 2019-12-10T11:23:20+01:00

Christian Hafner commented

2019-12-10 11:23:20 +01:00

System Information
Operating system: Windows 10 Pro 64-bit
Graphics card: NVIDIA Geforce GTX 1080 Ti

Blender Version
Broken: v2.80
Worked: (unknown)

Description
When exporting a NURBS curve to an .obj file, the vertices of the curve are listed in the "forward" order; but the curve references them in the reverse order. This yields the curve with its orientation reversed.

To reproduce the error:

In an empty file, create a Nurbs Curve.

(Optional) Move a vertex of the curve to break the symmetry; this makes it easier to see the error in the exported file.

File > Export > Wavefront (.obj)
Check "Write NURBS"
Export OBJ

Blender file:

OBJ file:

Details
The vertices in the file are listed in the order in which they appear in the curve.
The obj definition "curv 0.0 1.0 -1 -2 -3 -4" uses negative indexing, which counts the vertices starting from the bottom up, yielding the reverse orientation.
This is explained in the .obj specification start from line 652.

**System Information** Operating system: Windows 10 Pro 64-bit Graphics card: NVIDIA Geforce GTX 1080 Ti **Blender Version** Broken: v2.80 Worked: (unknown) **Description** When exporting a NURBS curve to an .obj file, the vertices of the curve are listed in the "forward" order; but the curve references them in the reverse order. This yields the curve with its orientation reversed. **To reproduce the error:** 1. In an empty file, create a Nurbs Curve. - (Optional) Move a vertex of the curve to break the symmetry; this makes it easier to see the error in the exported file. 2. File > Export > Wavefront (.obj) 3. Check "Write NURBS" 4. Export OBJ Blender file: ![curve_a.PNG](https://archive.blender.org/developer/F8204862/curve_a.PNG) OBJ file: ![curve_b.PNG](https://archive.blender.org/developer/F8204864/curve_b.PNG) **Details** The vertices in the file are listed in the order in which they appear in the curve. The obj definition "curv 0.0 1.0 -1 -2 -3 -4" uses negative indexing, which counts the vertices starting from the bottom up, yielding the reverse orientation. This is explained in the [.obj specification ](http://www.martinreddy.net/gfx/3d/OBJ.spec) start from line 652.

Christian Hafner commented

2019-12-10 11:23:20 +01:00

Added subscriber: @chafner

Eitan Traurig commented

2020-04-30 17:35:53 +02:00

Added subscriber: @EitanSomething

Eitan Traurig commented

2020-04-30 17:35:53 +02:00

Changed status from 'Needs Triage' to: 'Needs User Info'

Eitan Traurig commented

2020-04-30 17:35:53 +02:00

Is this still an issue with 2.83?

Ankit Meel commented

2020-09-07 23:54:20 +02:00

Added subscriber: @ankitm

Ankit Meel commented

2020-09-07 23:54:20 +02:00

Both relative and absolute indices are supported in OBJ for all types. Blender just happens to use it for Curves. The orientation is dependent on the importer and the axis transform the importer does.
Did you try importing the curve back into Blender to see if it was flipped?
Is it problematic for other apps ? If so, in the newer OBJ writer, we can write it in positive indices just like other objects as it's easy to change.

Both relative and absolute indices are supported in OBJ for all types. Blender just happens to use it for Curves. The orientation is dependent on the importer and the axis transform the importer does. Did you try importing the curve back into Blender to see if it was flipped? Is it problematic for other apps ? If so, in the newer OBJ writer, we can write it in positive indices just like other objects as it's easy to change.

Ankit Meel commented

2020-10-18 22:04:18 +02:00

Changed status from 'Needs User Info' to: 'Archived'

Ankit Meel closed this issue

2020-10-18 22:04:18 +02:00

Ankit Meel self-assigned this 2020-10-18 22:04:18 +02:00

Ankit Meel commented

2020-10-18 22:04:18 +02:00

No activity for more than a week. As per the tracker policy we assume the issue is gone and can be closed.

Thanks again for the report. If the problem persists please open a new report with the required information.

No activity for more than a week. As per the tracker policy we assume the issue is gone and can be closed. Thanks again for the report. If the problem persists please open a new report with the required information.

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.obj Export: NURBS curves exported with reverse orientation #72326