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Why are physical size measurements so important?

January 12, 2018 - 6:24am #1

Here at step 11 states: 

It is also important to make sure that the physical dimensions of your real-world object matches the Model Target Physical Length, Width and Height.

And here also mentions:

The size of the target needs to match the size of the object in real life

 

As long as the 3D scene scales are correct, then why is it so important to get the physical measurements correct?

I'm working with small target objects, a 12x12x12cm multi target cube and now i want to add a 2 x 3.5 x 5.5cm model to the scene. If i work as 1 unit = 1 meter, then the scale on the main multitarget would be 0.12, and everything rendered on that even smaller. I don't prefer to work at such a small scale, you often would tweak values that are in the thousandths decimal place, and the unity physics system functions better if you work at a scale that is based around 1.

So for that reason i setup my multitarget model as being 10x10x10 meters large, and this works great. However this means to match the scene, i will need to scale up the 3D Model Target. When i do this in Unity, it then becomes a 1.6 x 4.5 x 2.8 meter model.

 

So my question is, will having a 3D model/environment that is 83 times larger than the real world equivalent, still work for model targets? I haven't printed the model yet, so i wanted to confirm this beforehand.

Why are physical size measurements so important?

January 12, 2018 - 12:07pm #3

Hi Strasza,

I still don't quite understand the need for physical measurements, since if there's no other object in the scene with known measurements, then the phone can't tell whether something is 1 meter tall vs 10 meters tall. Anyways, my 3D model's scale will match the physical size, no distortions or anything. The trick for me is getting the model's scale to align with my cube's scale.

Cube is already multi-target. I'm excited to add a model target to the scene and see how it can interact with my cube multi-target. 

Why are physical size measurements so important?

January 12, 2018 - 10:18am #2

Hello PLGRM,

Model Targets use the size defined in the dataset when trying to detect the object. The best results are achieved when the physical and digital model are aligned in their size. However, Model Targets will still function if the digital model is defined with a different size than the physical model, as long as the scales are relative. We've seen various examples of this occurring, but some models (usually targets that aren't of the greatest quality for MT) will face difficulties if the scales between the two do not match.

My question for you is, are you using Model Targets to detect a cube? This will not be ideal as the target will no have sufficient geometry. I'd recommend using our Multi-Target feature for cube detection.

Thanks,

Vuforia Support

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