Improve USD camera import/export and round-tripping #112905

Denis Kovacs · 2023-09-26T14:45:31+02:00

Denis Kovacs commented

2023-09-26 14:45:31 +02:00

Improve USD camera import/export and round-tripping

Bugfix for camera USD import

wrong units, flipped shiftx / shifty values
clip_start to match Blender's property range (defined in rna_camera.cc)

Bugfix for camera USD export

wrong units (should be tenth of a stage unit for horizontal/vertical aperture and aperture offsets, focal length)
Auto sensor-fit with height > width (uses sensor_x instead of sensor_y)

Challenges/Limitations

Blender does not support aperture offsets in absolute values: shiftx and shifty store these as a fraction of the sensor size.
Blender only supports a single sensor size (either sensor_x or sensor_y, depending on Sensor Fit) and only one global aspect ratio for all cameras (defined using RenderData's xsch*xasp, ysch*yasp)
If Sensor Fit is set to Auto, Blender always uses sensor_x as the sensor size, regardless of whether sensor_y > sensor_x or not. So importing a camera from USD is best done with the Sensor Fit explicitly set to Horizontal or Vertical - this makes sure the respective sensor_x or sensor_y value is used, and makes the shift values more predictable when RenderData's aspect ratio does not exactly match the camera sensor's.

Testing

Create new Blender scene
Go to camera's object data properties,
Set Shift X to 0.1,
Set Shift Y to 0.2,
Set Clip Start to 0 (this will change to 0.000001 m due to rna_camera's RNA_def_property_range).
Export to a USD file, say Cameras.usda
Import Cameras.usda into Blender
Toggle between new vs. original camera views and compare their camera frames (note that the values for sensor size and shift values will necessarily be different if the camera's sensor fit is Vertical and the original camera's is Auto - however the visual result should be identical).
Open Cameras.usda with usdview (command line tool from the OpenUSD repo).
In the 3D View, turn on Camera>Camera Guides>Camera Frame, and set the camera with Camera>Select Camera>Camera, compare with Blender's camera frame.

# Improve USD camera import/export and round-tripping ## Bugfix for camera USD import - wrong units, flipped `shiftx` / `shifty` values - `clip_start` to match Blender's property range (defined in `rna_camera.cc`) ## Bugfix for camera USD export - wrong units (should be tenth of a stage unit for horizontal/vertical aperture and aperture offsets, focal length) - `Auto` sensor-fit with height > width (uses `sensor_x` instead of `sensor_y`) # Challenges/Limitations - Blender does not support aperture offsets in absolute values: `shiftx` and `shifty` store these as a fraction of the sensor size. - Blender only supports a single sensor size (either `sensor_x` or `sensor_y`, depending on Sensor Fit) and only one global aspect ratio for all cameras (defined using `RenderData`'s `xsch*xasp`, `ysch*yasp`) - If Sensor Fit is set to `Auto`, Blender always uses `sensor_x` as the sensor size, regardless of whether `sensor_y > sensor_x` or not. So importing a camera from USD is best done with the Sensor Fit explicitly set to `Horizontal` or `Vertical` - this makes sure the respective `sensor_x` or `sensor_y` value is used, and makes the shift values more predictable when `RenderData`'s aspect ratio does not exactly match the camera sensor's. # Testing - Create new Blender scene - Go to camera's object data properties, - Set `Shift X` to `0.1`, - Set `Shift Y` to `0.2`, - Set `Clip Start` to `0` (this will change to `0.000001 m` due to `rna_camera`'s `RNA_def_property_range`). - Export to a USD file, say `Cameras.usda` - Import `Cameras.usda` into Blender - Toggle between new vs. original camera views and compare their camera frames (note that the values for sensor size and shift values will necessarily be different if the camera's sensor fit is `Vertical` and the original camera's is `Auto` - however the visual result should be identical). - Open `Cameras.usda` with `usdview` (command line tool from the `OpenUSD` repo). - In the 3D View, turn on `Camera>Camera Guides>Camera Frame`, and set the camera with `Camera>Select Camera>Camera`, compare with Blender's camera frame.

Denis Kovacs added 1 commit 2023-09-26 14:45:42 +02:00

b973fb22e9 fixes to USD camera export/import for correct round-tripping.

Denis Kovacs requested review from Sybren A. Stüvel 2023-09-26 14:58:28 +02:00

Denis Kovacs requested review from Michael Kowalski 2023-09-26 14:59:06 +02:00

Sybren A. Stüvel refused to review 2023-09-26 16:55:04 +02:00

Sybren A. Stüvel added the

Download

What's New

Blender Studio

Manual

Developers Blog

Documentation

Benchmark

Blender Conference

Development Fund

One-time Donations