Converting from millimetres back to metres - object not converting back to metres #118886

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Nicholas-Fox · 2024-02-29T06:33:26+01:00

Nicholas-Fox commented

2024-02-29 06:33:26 +01:00

System Information
Operating system: Windows 11
Graphics card: Nvidia RTX 3070

Blender Version 4.01
Broken: (example: 2.80, edbf15d3c0, master, 2018-11-28, as found on the splash screen)
Worked: (newest version of Blender that worked as expected)
Conversion from mm to m not working

Exact steps for others to reproduce the error
Based on the default startup or an attached .blend file (as simple as possible).

**System Information** Operating system: Windows 11 Graphics card: Nvidia RTX 3070 **Blender Version** 4.01 Broken: (example: 2.80, edbf15d3c044, master, 2018-11-28, as found on the splash screen) Worked: (newest version of Blender that worked as expected) Conversion from mm to m not working **Exact steps for others to reproduce the error** Based on the default startup or an attached .blend file (as simple as possible).

Nicholas-Fox added the

labels 2024-02-29 06:33:26 +01:00

Nicholas-Fox commented

2024-02-29 06:46:56 +01:00

I have the basic Blender scene with a sphere that has a diameter of 2000mm, a camera and two area lights that I want to convert to metres. I change the unit scale from 0.001 to 1 and the scene properties aresimilarly change - unit scale to 1 and Length to metres. My sphere now measures 2000 metres and the camera an lights are sililarly converted so that their millimetre size now becomes asize in metres so not a straight conversion. If I now change the camera size to 1m (from the conversion value of 1000m) it becomes a single dot on the screen. So the conversion only works in one direction - from metres to millimetres.

Germano Cavalcante commented

2024-02-29 12:57:46 +01:00

Hi @Nicholas-Fox,

Thank you for reporting this issue. However, I'm not quite clear on the problem you're experiencing.

You mentioned that after converting the units from millimeters to meters, the sphere measures 2000 meters instead of 2000 millimeters. This seems incorrect, as the sphere's size should remain the same after the conversion.

Additionally, it's unclear why you're trying to convert the units for the camera and lights, as they don't have dimensions in the same way as objects like the sphere.

Could you please provide more specific and detailed steps to reproduce the issue? This will help us understand and address the problem more effectively.

Hi @Nicholas-Fox, Thank you for reporting this issue. However, I'm not quite clear on the problem you're experiencing. You mentioned that after converting the units from millimeters to meters, the sphere measures 2000 meters instead of 2000 millimeters. This seems incorrect, as the sphere's size should remain the same after the conversion. Additionally, it's unclear why you're trying to convert the units for the camera and lights, as they don't have dimensions in the same way as objects like the sphere. Could you please provide more specific and detailed steps to reproduce the issue? This will help us understand and address the problem more effectively.

Germano Cavalcante added

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labels 2024-02-29 12:57:56 +01:00

Nicholas-Fox commented

2024-02-29 22:03:08 +01:00

I start with the premise and knowledge that every object in Blender has a size - length, width, height... even the camera has a viewport size. I have a scene created in metres that contains spotlights, area lights, a plane and a cube that measures 2mx2mx2m. I now want to convert this scene to mm and change the setting in the Scene tab to millimetres and the scale to 0.001 as shown in the YouTube video shown here: https://www.youtube.com/watch?v=VihRvil3138&list=PL53RXasJr9ybzN9F_n_KYfpzkn8E2F9y0&index=116
The cube in my scene now measures 2 millimetres and everything else with dimensions in the scene is likewise affected, that is, everything in the scene gets shrunk so that it is no longer its original size.
So how about if we reverse the process and convert back to metres? Everything should convert nicely no? Before converting I create a new cube that measures 2000 millimetres x 2000 millimetres x 2000 millimetres. I now change the unit settings in the scene to metres and change the scale vale from 0.001 to 1 and reverse any other steps shown in the video I've linked to (please watch it). Following these changes my 2000 millimetre cube now measures (using again the measuring tool in Blender) 2000 metres. Clearly this is incorrect and the change from millimetres to metres in Blender is not the change expected or should be. 1 metres is always 1000mm. This is clearly a fault/bug in Blender which divides dimensions in a scene by 1000 when converting from metres to millimetres and multiples dimensions by 100 when converting from millimetres to metres and this procedure affects every object in a scene.
I would urge you to watch the YouTube video I have linked to as this demonstrates the process I followed. The conversion probably works fine for an empty scene, but once you introduce 3D object into the scene, Blender fails to do a correct conversion.

I start with the premise and knowledge that every object in Blender has a size - length, width, height... even the camera has a viewport size. I have a scene created in metres that contains spotlights, area lights, a plane and a cube that measures 2mx2mx2m. I now want to convert this scene to mm and change the setting in the Scene tab to millimetres and the scale to 0.001 as shown in the YouTube video shown here: https://www.youtube.com/watch?v=VihRvil3138&list=PL53RXasJr9ybzN9F_n_KYfpzkn8E2F9y0&index=116 The cube in my scene now measures 2 millimetres and everything else with dimensions in the scene is likewise affected, that is, everything in the scene gets shrunk so that it is no longer its original size. So how about if we reverse the process and convert back to metres? Everything should convert nicely no? Before converting I create a new cube that measures 2000 millimetres x 2000 millimetres x 2000 millimetres. I now change the unit settings in the scene to metres and change the scale vale from 0.001 to 1 and reverse any other steps shown in the video I've linked to (please watch it). Following these changes my 2000 millimetre cube now measures (using again the measuring tool in Blender) 2000 metres. Clearly this is incorrect and the change from millimetres to metres in Blender is not the change expected or should be. 1 metres is always 1000mm. This is clearly a fault/bug in Blender which divides dimensions in a scene by 1000 when converting from metres to millimetres and multiples dimensions by 100 when converting from millimetres to metres and this procedure affects every object in a scene. I would urge you to watch the YouTube video I have linked to as this demonstrates the process I followed. The conversion probably works fine for an empty scene, but once you introduce 3D object into the scene, Blender fails to do a correct conversion.

Germano Cavalcante commented

2024-02-29 23:19:20 +01:00

It seems there might be some confusion regarding the unit conversion in Blender.
When you the scale value to 0.001, the conversion is correct.

Just like 2mm corresponds to 2m, 2000mm corresponds to 2000m.

Not a bug AFAICS, so closing.

Feel free to comment if there is misunderstanding., which is the expected behavior.

It seems there might be some confusion regarding the unit conversion in Blender. When you the scale value to 0.001, the conversion is correct. Just like 2mm corresponds to 2m, 2000mm corresponds to 2000m. Not a bug AFAICS, so closing. Feel free to comment if there is misunderstanding., which is the expected behavior.

Germano Cavalcante closed this issue

2024-02-29 23:19:23 +01:00

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labels 2024-02-29 23:19:24 +01:00

Nicholas-Fox commented

2024-03-01 00:27:45 +01:00

No misunderstanding here mate and 2m is always 2000mm and 2000mm does not convert to 2000m.

Germano Cavalcante commented

2024-03-01 00:40:41 +01:00

The cube when added has 2000 BU (Blender units).
The BU is usually 1 meter, but when changing the scale to 0.001, it visually becomes 1 millimeter.
That's why you see 2000 mm.

The cube when added has 2000 BU (Blender units). The BU is usually 1 meter, but when changing the scale to 0.001, it visually becomes 1 millimeter. That's why you see 2000 mm.

Nicholas-Fox commented

2024-03-01 01:13:40 +01:00

I've attached the scene to show what Blender did to it during conversion. The lights are way off and were approximately 2.4m high when created. They are no longer at that height and doing a conversion makes zero difference. Try changing the Floor scale 1 1 or 0.001, the Scene scale from 1 to 0.001 and the units to metres and/or millimetres then add cubes and cameras in the 3d viewport and you'll see how they appear. It would seem that the 'conversion' is only applicable to empty scenes and only then does it work correctly while converting while objects are in a scene doesn't as Blender fails to correctly adjust things like light height and basically seems to ignore them.

m-mm conversion.blend

1.1 MiB

Nicholas-Fox reopened this issue

2024-03-01 01:13:43 +01:00

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Germano Cavalcante commented

2024-03-04 16:25:59 +01:00

I imagine that perhaps you are confusing the issue and actually wanting to describe this one:
#116497: Inconsistent size of Added Objects when changing the overlay grid scale or unit scale

Could you check?
As far as I can see, there is no conversion error.
You always mention about "add cubes". So perhaps you are referring to the size of the object (which actually changes and is something known, as the size depends on the first time an object was added. The size settings is saved. This is indeed confusing for some users, that's why it was reported in #116497).

I imagine that perhaps you are confusing the issue and actually wanting to describe this one: #116497: Inconsistent size of Added Objects when changing the overlay grid scale or unit scale Could you check? As far as I can see, there is no conversion error. You always mention about "add cubes". So perhaps you are referring to the size of the object (which actually changes and is something known, as the size depends on the first time an object was added. The size settings is saved. This is indeed confusing for some users, that's why it was reported in #116497).

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labels 2024-03-04 16:26:08 +01:00

Germano Cavalcante commented

2024-03-25 16:07:00 +01:00

No activity for more than a week. As per the tracker policy we assume the issue can be closed.
I will assume it is a duplicate of #116497

No activity for more than a week. As per the tracker policy we assume the issue can be closed. I will assume it is a duplicate of #116497

Germano Cavalcante closed this issue