USD Import - camera field of view wrong #100028

New Issue

Russ Andersson · 2022-07-27T16:59:26+02:00

Russ Andersson commented

2022-07-27 16:59:26 +02:00

The USD camera import does not produce a usable camera. It sets the focal length, but not the camera sensor size (horizontal and vertical aperture), so the camera field of view is wrong all of the time. The sensor size information is in the USD file, but is ignored for perspective cameras. Setting these two values is essential to a camera import, not optional, ie this is a bug, not a new feature.

If you accept the focal length as having arbitrary unknown units, you can and must do the same thing for sensor size/aperture. Since the values are generally not in mm, the user's recourse is to enter the values into blender manually after locating the correct aperture values using usdview or by converting to USDA and opening the file in a text editor and hunting them down.

There's an additional hazard: blender limits sensor size to 1 to 100 mm. Due to USD's definition of FL/HA/VA units, the sensor size (and/or FL) may (often) fall outside that range. If the value is outside the valid range, the USD camera importer should simply rescale FL, HA, and VA by the same value, chosen to bring them in range.

https://developer.blender.org/diffusion/B/browse/master/source/blender/io/usd/intern/usd_reader_camera.cc
https://developer.blender.org/diffusion/B/browse/master/source/blender/blenkernel/BKE_camera.h

The USD camera import does not produce a usable camera. It sets the focal length, but not the camera sensor size (horizontal and vertical aperture), so the **camera field of view is wrong all of the time**. The sensor size information is in the USD file, but is ignored for perspective cameras. Setting these two values is essential to a camera import, not optional, ie this is a bug, not a new feature. If you accept the focal length as having arbitrary unknown units, you can and must do the same thing for sensor size/aperture. Since the values are generally not in mm, the user's recourse is to enter the values into blender manually after locating the correct aperture values using usdview or by converting to USDA and opening the file in a text editor and hunting them down. There's an additional hazard: blender limits sensor size to 1 to 100 mm. Due to USD's definition of FL/HA/VA units, the sensor size (and/or FL) may (often) fall outside that range. If the value is outside the valid range, the USD camera importer should simply rescale FL, HA, and VA by the same value, chosen to bring them in range. https://developer.blender.org/diffusion/B/browse/master/source/blender/io/usd/intern/usd_reader_camera.cc https://developer.blender.org/diffusion/B/browse/master/source/blender/blenkernel/BKE_camera.h

Russ Andersson commented

2022-07-27 16:59:26 +02:00

Added subscriber: @ssontech

Russ Andersson commented

2022-07-27 17:11:40 +02:00

Untested example/proposed code change to fix this:

58,59c58,62
<   bcam->sensor_x = horAp.Get<float>();
<   bcam->sensor_y = verAp.Get<float>();
---
>   /* TODO(@makowalski): support sensor size. */
> #if 0
>    bcam->sensor_x = 0.0f;
>    bcam->sensor_y = 0.0f;
> #endif

62,79d64
<   if (bcam->sensor_x != 0.0f && bcam->sensor_y != 0.0f)
<       while (bcam->sensor_x < 1.0f || bcam->sensor_y < 1.0f)
<       {
<         bcam->lens *= 10.0f;
<         bcam->sensor_x *= 10.0f;
<         bcam->sensor_y *= 10.0f;
<         bcam->shiftx *= 10.0f;
<         bcam->shifty *= 10.0f;
<       };
<   while (bcam->sensor_x > 100.0f || bcam->sensor_y > 100.0f)
<   {
<       bcam->lens *= 0.1f;
<       bcam->sensor_x *= 0.1f;
<       bcam->sensor_y *= 0.1f;
<       bcam->shiftx *= 0.1f;
<       bcam->shifty *= 0.1f;
<   };
<

Untested example/proposed code change to fix this: ``` 58,59c58,62 < bcam->sensor_x = horAp.Get<float>(); < bcam->sensor_y = verAp.Get<float>(); --- > /* TODO(@makowalski): support sensor size. */ > #if 0 > bcam->sensor_x = 0.0f; > bcam->sensor_y = 0.0f; > #endif 62,79d64 < if (bcam->sensor_x != 0.0f && bcam->sensor_y != 0.0f) < while (bcam->sensor_x < 1.0f || bcam->sensor_y < 1.0f) < { < bcam->lens *= 10.0f; < bcam->sensor_x *= 10.0f; < bcam->sensor_y *= 10.0f; < bcam->shiftx *= 10.0f; < bcam->shifty *= 10.0f; < }; < while (bcam->sensor_x > 100.0f || bcam->sensor_y > 100.0f) < { < bcam->lens *= 0.1f; < bcam->sensor_x *= 0.1f; < bcam->sensor_y *= 0.1f; < bcam->shiftx *= 0.1f; < bcam->shifty *= 0.1f; < }; < ```

Omar Emara commented

2022-08-01 15:40:42 +02:00

Added subscriber: @OmarEmaraDev

Omar Emara commented

2022-08-01 15:40:42 +02:00

Changed status from 'Needs Triage' to: 'Confirmed'

Omar Emara commented

2022-08-01 15:40:42 +02:00

I guess the module can mark this as a TODO or a known issue.
Since you seem knowledgeable about this, have you considered submitting a patch yourself? https://wiki.blender.org/wiki/Process/Contributing_Code

I guess the module can mark this as a TODO or a known issue. Since you seem knowledgeable about this, have you considered submitting a patch yourself? https://wiki.blender.org/wiki/Process/Contributing_Code

Russ Andersson commented

2022-08-01 16:01:33 +02:00

My proposed change is based on a quick look at this local code only; I have no "big picture" understanding of blender internals at all and may be completely missing some other concern. So my thought is that it's better for an actual USD developer to consider it.

Sonny Campbell commented

2022-08-25 12:19:24 +02:00

Added subscriber: @SonnyCampbell_Unity

Sonny Campbell commented

2022-08-25 12:19:24 +02:00

@ssontech Have you got a sample USD/blend file to test against? I can happily take a look at this for you

Russ Andersson commented

2022-08-31 21:10:55 +02:00

Sorry for the delay, here's an example file. Images at https://www.ssontech.com/pub/GoingThruPhase.php

phaseExample.zip

Sorry for the delay, here's an example file. Images at https://www.ssontech.com/pub/GoingThruPhase.php [phaseExample.zip](https://archive.blender.org/developer/F13442129/phaseExample.zip)

Sonny Campbell self-assigned this 2022-09-19 15:23:31 +02:00

blender-admin commented

2023-01-30 23:22:26 +01:00

This issue was referenced by f359a39d11

This issue was referenced by f359a39d11511721c5a201be6f6dcaa6d8780792

Michael Kowalski commented

2023-01-30 23:26:43 +01:00

Changed status from 'Confirmed' to: 'Resolved'

Michael Kowalski closed this issue

2023-01-30 23:26:43 +01:00

Bastien Montagne added this to the Pipeline, Assets & IO project 2023-02-09 15:40:02 +01:00

Bastien Montagne removed this from the Pipeline, Assets & IO project 2023-02-10 12:49:18 +01:00

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USD Import - camera field of view wrong #100028