Confusing mesh coordinate

[FlyCole]

Hi,
I have a question about mesh coordinate. I tried to extract mesh from ngp and use the mesh as a real-world digital twin in the following tasks. In that case, I need to keep the real-world coordinate rather than the ngp convention. I'm aware that there's a transformation between ngp coordinate and opencv coordinate. So I transformed the coordinate and got the correct real world pose for the mesh. However, if I set offset in the config file with only one value, it seems the final extracted mesh transformed not only from the axis I specified. The figure below shows the difference when I set offset to (0, 0.4, 0) . (The right bottom one is after offset)
May I ask is there some hard coded translation for the offset or did I use a wrong transformation?

[GaroleAtharva]

what aabb_scale did you use?

It’s possible that the unexpected transformation behavior might be related to the aabb (axis-aligned bounding box) scale used in instant-ngp. The aabb_scale can impact how transformations and offsets are applied, especially if there’s a mismatch between the instant-ngp coordinate system and the real-world system you’re targeting.

Just a thought - could be totally wrong, though

[FlyCole]

Hi, I'm actually using aabb_scale = 1. But thanks for your advice, it gives me some insights!

[FlyCole]

I double-checked it and found out it is related to offset itself. The figure below shows what it would be when I move it differently and it's very interesting. The top left one is when the offset is [0, 0, 0]. If I use [0, 0.4, 0], it would move to the center one; Then if I use [0, 0.8, 0], it would move to the bottom right. If I use '[0.4, 0.4, 0]', it would move to to top middle. However, if I use [0.4, 0.4, 0.4], it would move back to the top left again! Then I also checked, as long as the three numbers are the same, it would always be back to the origin. I haven't figured out how to align it in real-world. But thanks for your insights!

[GaroleAtharva]

Did you find out what offset values you should be using?

[FlyCole]

The quick answer is that if I'm using [0, 0.4, 0] as the offset during training, I have to move the mesh back to the right position by [0, -0.4, 0.4] (for different coordinate systems that might be different). However, I didn't have enough time to figure out the reason behind it.