USD: Adding an option to convert the scene's meters per unit value #122804

Charles Wardlaw · 2024-06-05T22:17:22+02:00

Charles Wardlaw commented

2024-06-05 22:17:22 +02:00

This rescales the whole scene by its root transform to match the same visual size while not forcing the user to wait for scale to be applied to each object.

This is requested by studios whose main applications / USD scenes are in CM, because referencing and payloading scenes from disparate scales can cause issues at resolution time.

This rescales the whole scene by its root transform to match the same visual size while not forcing the user to wait for scale to be applied to each object. This is requested by studios whose main applications / USD scenes are in CM, because referencing and payloading scenes from disparate scales can cause issues at resolution time.

Charles Wardlaw added 1 commit 2024-06-05 22:17:33 +02:00

USD: Adding a Convert to Centimeters option, which rescales the whole scene by its root transform to match the same visual size while not forcing the user to wait for scale to be applied to each object. c67e1cb079

Charles Wardlaw requested review from Michael Kowalski 2024-06-05 22:41:50 +02:00

Charles Wardlaw requested review from Jesse Yurkovich 2024-06-05 22:42:02 +02:00

Michael Kowalski commented

2024-06-05 22:47:38 +02:00

Thanks for porting this @CharlesWardlaw ! I was thinking that the unit conversion should be made more generic to handle arbitrary unit scaling, not just centimeters. The initial USD branch implementation supported centimeters only, but I always felt that this prototype is too limited in that regard. It shouldn't be hard to extend this to handle other units. What do you think?

Dhruv Govil commented

2024-06-05 22:52:33 +02:00

First-time contributor

I agree that the functionality would be useful (even though we prefer meters ourselves).

However, I think this might be better served as a dropdown enum choice of common units? With a default of Meters, and any other unit sizes as options (could just be meters and centimetres to start). In fact, I'd recommend that the input to the operator itself actually be a float that defaults to 1 (metersPerUnit=1.0) and the dropdown just be a UI set of preset values.

That way it's generalizable and easy to add more unit sizes in the future, since some studios use imperial units. By generalizing it to a scalar , that enum just needs to change the scalar without modifying the rest of the code.

This is generally how I implemented it in other DCCs and our internal pipeline as well.

I agree that the functionality would be useful (even though we prefer meters ourselves). However, I think this might be better served as a dropdown enum choice of common units? With a default of Meters, and any other unit sizes as options (could just be meters and centimetres to start). In fact, I'd recommend that the input to the operator itself actually be a float that defaults to 1 (metersPerUnit=1.0) and the dropdown just be a UI set of preset values. That way it's generalizable and easy to add more unit sizes in the future, since some studios use imperial units. By generalizing it to a scalar , that enum just needs to change the scalar without modifying the rest of the code. This is generally how I implemented it in other DCCs and our internal pipeline as well.

👍 1

Charles Wardlaw commented

2024-06-05 23:14:43 +02:00

It's easy enough to add-- I'll send a follow up in a few.

Charles Wardlaw added 1 commit 2024-06-06 20:45:10 +02:00

Addressing comments for flexibility. 9d4b995328

Charles Wardlaw commented

2024-06-06 20:45:43 +02:00

I think this is correct, but I'm going to do a bunch more tests first. 🤣

Charles Wardlaw changed title from ~~USD: Adding a Convert to Centimeters option~~ to USD: Adding an option to convert the scene's meters per unit value

2024-06-06 20:48:17 +02:00

Charles Wardlaw added this to the USD project 2024-07-11 23:15:35 +02:00

Michael Kowalski reviewed 2024-07-12 20:23:55 +02:00

source/blender/editors/io/io_usd.cc

						
				@ -159,0 +164,4 @@

				    {USD_SCENE_UNITS_INCHES, "INCHES", 0, "Inches", "Scene scale of 0.0254"},

				    {USD_SCENE_UNITS_FEET, "FEET", 0, "Feet", "Scene scale of 0.3048"},

				    {USD_SCENE_UNITS_YARDS, "YARDS", 0, "Yards", "Scene scale of 0.9144"},

				    {USD_SCENE_UNITS_CUSTOM, "CUSTOM", 0, "Custom", "Specify a custom scene scale value"},

Michael Kowalski commented

2024-07-12 20:23:55 +02:00

Minor point: the help for the Custom option is "Specify a custom scene scale value". However, the custom value is actually in meters-per-unit. Would it be better to be consistent? I.e., either have the help for all the menu items be in meters-per-unit, or have the Custom option be a scene scale? The former option (using meters-per-unit for all items) would probably be less work and might fit better with the USD conventions. Again, this might not be an important issue.

Minor point: the help for the `Custom` option is "Specify a custom scene scale value". However, the custom value is actually in meters-per-unit. Would it be better to be consistent? I.e., either have the help for all the menu items be in meters-per-unit, or have the `Custom` option be a scene scale? The former option (using meters-per-unit for all items) would probably be less work and might fit better with the USD conventions. Again, this might not be an important issue.

Michael Kowalski reviewed 2024-07-12 22:29:37 +02:00

source/blender/io/usd/intern/usd_writer_transform.cc

						
				@ -45,1 +45,3 @@

				  if (!usd_export_context_.export_params.convert_orientation) {

				  if ((!usd_export_context_.export_params.convert_orientation ||

				       usd_export_context_.export_params.convert_scene_units))

				  {

Michael Kowalski commented

2024-07-12 22:29:37 +02:00

I think this conditional should be

 if (!(usd_export_context_.export_params.convert_orientation ||
       usd_export_context_.export_params.convert_scene_units))

Note the ! is outside the innermost parentheses. Without this change, no transform is applied to root prims if the Root Prim export param is empty. To reproduce, export the default cube to USDA with an empty Root Prim path with Convert Scene Units set to something other than meters. Note that the prims don't have the scaling set.

I think this conditional should be ``` if (!(usd_export_context_.export_params.convert_orientation || usd_export_context_.export_params.convert_scene_units)) ``` Note the `!` is outside the innermost parentheses. Without this change, no transform is applied to root prims if the `Root Prim` export param is empty. To reproduce, export the default cube to USDA with an empty `Root Prim` path with `Convert Scene Units` set to something other than meters. Note that the prims don't have the scaling set.

Michael Kowalski reviewed 2024-07-12 23:01:11 +02:00

source/blender/io/usd/usd.hh

						
				@ -135,2 +145,3 @@

				  bool allow_unicode = false;

				  eUSDSceneUnits convert_scene_units = eUSDSceneUnits::USD_SCENE_UNITS_METERS;

				  float meters_per_unit = 1.0f;

Michael Kowalski commented

2024-07-12 23:01:11 +02:00

Just a question that occurred to me: is convert_scene_units redundant in this case? I.e., would it be sufficient to just have meters_per_unit set appropriately in io_usd.cc and use that to compute the scale? I know this would change some of the logic elsewhere to determine whether to apply scaling by checking if meters_per_unit is close to 1.0, so there are tradeoffs with either approach.

Just a question that occurred to me: is `convert_scene_units` redundant in this case? I.e., would it be sufficient to just have `meters_per_unit` set appropriately in `io_usd.cc` and use that to compute the scale? I know this would change some of the logic elsewhere to determine whether to apply scaling by checking if `meters_per_unit` is close to 1.0, so there are tradeoffs with either approach.

Jesse Yurkovich referenced this pull request

2024-07-25 02:18:52 +02:00

USD Targets for blender 4.3 #123008

Michael Kowalski referenced this pull request

2024-10-07 19:55:22 +02:00

USD Targets for blender 4.4 #128717

Aras Pranckevicius commented

2024-10-08 09:10:00 +02:00

This whole units thing reminded me of #128337 which also attempts to add units dropdown to another I/O type. Maybe it would be good to unify that across various I/O types and use shared code?

This whole units thing reminded me of https://projects.blender.org/blender/blender/pulls/128337 which also attempts to add units dropdown to another I/O type. Maybe it would be good to unify that across various I/O types and use shared code?

This pull request has changes conflicting with the target branch.

source/blender/editors/io/io_usd.cc
source/blender/io/usd/intern/usd_writer_camera.cc
source/blender/io/usd/usd.hh

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USD: Adding an option to convert the scene's meters per unit value #122804

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