How do we obtain origin (0,0,0) for a 3D Model?

PIX4Dmapper PIX4Dmapper Questions/Troubleshooting
1

Hi Pix4D Community!
I use Pix4D Mapper for generating 3D mesh models using drone imagery of buildings.

I want to understand:

  1. What is the coordinate frame of a resulting 3D mesh model,
  2. How is the origin of the 3D mesh model decided?

When I import the .obj file in Blender, sometimes I see the origin much above the building and sometimes in between the building and sometimes translated to a much different position. I obtain the offset (.xyz) file which lets me know the offset from this origin, but is there a way I can understand the coordinate system and how is this origin decided in the first place?

Can someone explain this? Thanks!

2

Hi @ashlyn.dsouza,

Welcome to the Pix4D Community :handshake:.

The coordinate frame of a resulting 3D mesh model generated by PIX4Dmapper is not inherently georeferenced. This means that the origin of the 3D mesh model is decided based on the internal coordinate system used by PIX4Dmapper during processing, which is arbitrary and not related to real-world coordinates.

When you import the .obj file into Blender or any other 3D software, the position of the origin you observe is a result of this internal coordinate system. The origin can appear at different positions relative to the building because it is not aligned with any geospatial reference by default.

However, to georeference your 3D mesh model, you can use the offset.xyz file that accompanies the 3D mesh when it is exported from PIX4Dmapper. The offset file contains the information needed to align the 3D mesh with the point cloud, which is georeferenced. By adding the offset.xyz file together with the 3D mesh files when uploading the 3D mesh, you enable the alignment of the 3D mesh to the point cloud and thus georeference it.

The offset file can be found in the ..\1_initial\params folder of your PIX4Dmapper project. If this folder does not exist, you can generate the offset file by selecting the Camera Internals and Externals, AAT, BBA option for step 1. Initial Processing under the Calibration tab and re-running Step 1.

To summarize, the origin of the 3D mesh model in PIX4Dmapper is determined by the software’s internal processing and does not have a real-world reference unless you use the offset.xyz file to align and georeference it with the point cloud data.

I hope this clarifies how the coordinate system and origin for 3D mesh models work in PIX4Dmapper. If you have any more questions or need further assistance, feel free to reach out!

Have a great day! :blush:

Daniele

3

Can Pix4D Mapper generated OBJ, FBX (or other file formats) be georeferenced to view and measure (XYZ) either in Pix4D or in 3rd party model viewers?

4

Hi @Graeme_Heinrich,

Sure, the 3D Textured Mesh can be visualized directly in PIX4Dmapper. You need to enable the mesh in the layers:

image
image865×549 59.5 KB

With external software, you need to use the _offset.xyz file as described here:

Cheers,
Daniele

5

Daniele,
Thanks for the reply. What external software can be used to create a georeferenced OBJ? We are using Bentley Acute 3D viewer, and would like the ability to interrogate (in 3D) a georeferenced OBJ, using that. Is there a process you know of to achieve this?

6

Hi @Graeme_Heinrich,

I’m not familiar with Bentley, so I will wait for Pix4D Community users with more knowledge of this software to reply.
In general, when you open an OBJ file, you are asked to define an offset file (XYZ format).