Autodesk Forge提取RVT几何至OBJ出现400错误及相关疑问

Let’s tackle your two main questions one by one, starting with the 400 error you’re hitting when calling the Model Derivative API.

1. Fixing the 400 Bad Request Error #

Looking at your code, there’s a critical data type mismatch in the objectIds field that’s almost certainly causing the error:

Issue in Java Code #

Your current code converts integer objectIds to strings before adding them to the payload:

List objectIdList = new ArrayList();
objectIds.forEach(e -> objectIdList.add(Integer.toString((Integer) e)));

The Model Derivative API expects objectIds to be an array of integers, not strings. This type mismatch will trigger a 400 Bad Request.

Corrected Java Code #

Update that section to keep the values as integers:

List<Integer> objectIdList = new ArrayList<>();
objectIds.forEach(e -> objectIdList.add((Integer) e));

Additional Checks to Rule Out Other Problems #

• Verify the URN: Ensure the URN you’re passing is correctly Base64-encoded (most implementations strip trailing = characters, which is required for the API).
• Check Token Scopes: The access token used for the API call must include both data:read and data:write scopes. Double-check your token generation logic to confirm these are included.
• Validate modelGuid: Make sure the modelGuid matches the GUID of the model in your Viewer instance (you can retrieve this via viewer.model.getDocumentNode().getGuid()).
• Confirm Payload Structure: Ensure your final payload matches the official schema—for example, the output.formats.type should be obj (lowercase), though your Java SDK’s TypeEnum.OBJ should handle this correctly.

2. Format Support Questions #

Can I Extract Geometry from RVT to OBJ Directly? #

No, direct translation from RVT to OBJ is not supported by the Model Derivative service. As you noted, the official supported translations for RVT only include formats like SVF, SVF2, IFC, and DWG—OBJ isn’t on that list.

Can I Use SVF to Extract Geometry? #

You can’t use the Model Derivative API to convert SVF to OBJ (the API only accepts source design files like RVT as input, not intermediate formats like SVF). However, you can extract geometry directly from the SVF using the Forge Viewer’s API:

• Use the Viewer’s selection tools to get the selected objects.
• Traverse each object’s geometry to extract vertices, faces, normals, and UV data.
• Manually construct the OBJ file content using this extracted data (you’ll also need to generate a corresponding MTL file if you want to include material information).

There are open-source code snippets available that demonstrate this workflow—for example, iterating over Mesh instances in the Viewer and converting their raw data to OBJ format.

内容的提问来源于stack exchange，提问作者Widnmax J