Scale overall robot in XML file without editing XML #330
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Can we scale the robot model in the XML file without editing the XML itself? like: mujoco.MjModel.from_xml_path(
file_name="path_to_xml",
globalScaling=10.0)my robot needs to be twice the size according to the bounding box in fusion360. (The box is the bounding box) EDIT: The bounding box was not correctly specified ImagesThis urdf export is from fusion with fusion2urdf exporter. This model is then converted to XML with compile.cc
In pybullet
Inertias, masses, joints, etc have been exported properly, but not the meshes, they are half the size In Mujoco
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Replies: 5 comments 6 replies
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That's a good question. At the C API level, the route to creating a MuJoCo mjModel always goes through XML. Once an mjModel is created, scaling like that can't be done through the API. That means that scaling like you suggest does need to happen by creating a modified XML file, even if we hide it behind an API. We've chosen to make the MuJoCo python bindings are a thin layer on top of the C APIs, so such functionality doesn't exist. Where it could live might be the PyMJCF sub-library in dm_control. Another thing we talked about was building a better For your case, I think the quickest route forward is to figure out why the export produces meshes of the wrong sizes, and make a fix either to fusion2urdf, or to MuJoCo's URDF importer, depending on the cause. |
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I have used fusion2urdf and then compile.cc to convert it to an XML relatively easily. However, upon conversion, the size of the robot in the urdf that was generated from fusion2urdf fit correctly when rendered in pybullet as was in the CAD software. When converting to XML using compile.cc, the generated xml file was half the size.(1/8th in volume). Although the masses and the inertias were exported correctly. Note: The box is the approximate bounding box of the robot In bullet
After compile.cc
After compile.cc and scaled meshes to 2xScaling meshes to 2x in ``, the size fits, and as expected the joints are not correct
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OK. Given the same URDF works in Bullet, it's likely that there's a problem with MuJoCo's URDF importer. Would you be able to share the generated URDF and maybe the assets? |
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I cannot give the source, however, I have replicated the same effect with a 4-bar mechanism. Here are the files: There is a script to launch it in pybullet as well as one in mujoco. In the produced XML (from <option gravity="0 0 0" collision="predefined" />
<worldbody> <!--within <worldbody>-->
<light diffuse=".5 .5 .5" pos="0 -2 2" dir="0 1 -1" />
<body pos="0 0 0">
<geom type="box" size="1.05 0.15 1.05" rgba="1 1 1 .3" />
</body>
</worldbody>In pybulletSize: as defined in cad softwareScale: 1: 1 (if we assume 1=1m in pybullet)
In mujocoSize: 1/2 in length, 1/8th in volumeScale: 1: 0.5 (if we assume 1=1m in mujoco)
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defines a box that is 2.1m x 2.1m x 0.3m, since the size attribute on Does that explain the problem? |
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Ah yes, this was the issue. My mistake!😊 |
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shall I open an issue for this?
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It's very much on our mind but we need to articulate exactly what we want to do, so don't worry about it for now. |
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@nimrod-gileadi , I manually translated a Human3.6M Walkmujoco.human3.6m.walk.mp4When doing this, the things I had to scale down(or up) some of the the data sequentailly in the tags: <geom: pos size />
<body: pos />
<inertial: pos /> <!-- Altough, this was eliminated as I didn't need inertial properties in the final xml -->Although this is a simple example, perhaps could be loaded and manipulated like this: model = mujoco.MjModel.from_xml_path("robot.xml")
data = mujoco.MjData(model)
# via named access
data.body("top_level_body_name").scale= 1.25 # changes value of the pos, size while manintaing the origin in position |
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Nice work. As I mentioned, scaling should be done on the model (rather than the data), and at the moment MuJoCo doesn't support such modifications once a model is "compiled" (i.e after from_xml_path). PyMJCF allows the modification of the XML structure before compilation, so probably scaling should go there. |
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<geom type="box" size="1.05 0.15 1.05" rgba="1 1 1 .3" />defines a box that is 2.1m x 2.1m x 0.3m, since the size attribute on
geomspecifies half-size.Does that explain the problem?