How modify b3dm coordinates?

How does each building represent its own coordinates in 3DTILES? Is the property RTC-CENTER used? I want to get each building coordinates, but b3dm is binary, not very convenient to get, is there any good way? These building coordinates can be modified?

The 3d-tiles-tools are offering some functions that can be helpful here.

You can

  • install it with npm install 3d-tiles-tools, and then run it with npx 3d-tiles-tools ...
  • or clone the repository, and run npx ts-node ./src/main.ts ... in the cloned repository

The relevant functions are

  • b3dmToGlb to extract the GLB from a B3DM file
  • glbToB3dm to create a simple, default B3DM file from a GLB

Note: The question about what should happen with the RTC_CENTER is not yet clear. There is a recent PR where this came up, but it is not yet decided what the final solution will be.

If your intention is to …

  • extract the GLB from the B3DM
  • modify the GLB
  • create a B3DM from the GLB

then it is not clear what should happen with the RTC_CENTER in this process. One approach that could work in this case is to use the state from the linked PR, i.e. the branch at GitHub - CesiumGS/3d-tiles-tools at apply-rtc-to-glb . With this branch, the behavior will be:

  • when you extract the GLB from the B3DM with b3dmToGlb, then it will transform the GLB with the RTC_CENTER
  • then you can modify the (transformed) GLB
  • then you can create a B3DM from the (transformed) GLB with glbToB3dm.

The resulting B3DM file will then not define a RTC_CENTER any more, because that will then already be part of the GLB - so the GLB should still be at the right position, even without the RTC_CENTER.

Note that other information from the B3DM, e.g. batch table data, would also be lost in this process - from your screenshot, it looks like there is no batch table data, but it may be worth mentioning. As I said: The linked PR is only a draft, and we’ll have to see how to move forward from that.

If you have any feedback about the desired behavior and how the RTC_CENTER should be handled, then we can consider this for our next steps.

thank you for your reply.
My goal is to modify the position of these models. Which attribute information of b3dm should I modify, or what other method should I use. B3dm information is binary and processed

Maybe there are some additional details that have to be considered, but generally, it should be possible to…

If the question is about how to specifically modify the positions of a certain building, then there are different options for that. One approach could be to just import the GLB into Blender and perform the modifications there.

thank you for your reply. but i have some questions.In b3dm under 3dtiles, these binary data are very inconvenient to view, is there any tool to convert him? Convert to normal English strings. It can be viewed directly on txt.

like red part

Most of this data is the actual GLB contents. After extracting this from the B3DM with the b3dmToGlb command of the 3d-tiles-tools, you can inspect this data in different ways. And depending on what exactly you want to analyze here, there are different options.

But a relatively easy and versatile one could be to use the glTF Tools - Visual Studio Marketplace plugin in VSCode. After installing this, you can…

Right-click the GLB file and select “glTF: Import from GLB”

Cesium GLB 001

(and then confirm the location for the .gltf file)

Then you can obtain information about the glTF itself, by looking at the glTF JSON, and you can right-click, for example, on one of the accessors and select “glTF: Inspect Data”:

The data will then be displayed in the window in the lower left - here, for example, the indices of the mesh: