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Add distance sensing for SDF geoms #2216

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dyackzan opened this issue Nov 6, 2024 · 0 comments · May be fixed by #2218
Open

Add distance sensing for SDF geoms #2216

dyackzan opened this issue Nov 6, 2024 · 0 comments · May be fixed by #2218
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enhancement New feature or request

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@dyackzan
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dyackzan commented Nov 6, 2024 •
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The feature, motivation and pitch

The distance sensor returns the distance between two bodies/geoms normally, but if one of the elements is an SDF geom, then it will only return the penetration distance if the geoms are in contact. So if the objects are not in contact then the distance sensor doesn't actually sense the distance and will just return the cutoff value.

I'll make this a feature request rather than a bug since this behavior seems intentional/place-holding based on the mjc_SDF function that gets used when a distance sensor between an SDF and most other geom types is created.

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Additional context

I used the following model to test:

<mujoco model="distance_testing">
    <extension>
        <plugin plugin="mujoco.sdf.torus">
            <instance name="torus">
                <config key="radius1" value="0.35"/>
                <config key="radius2" value="0.15"/>
            </instance>
        </plugin>
    </extension>

    <asset>
        <mesh name="torus">
            <plugin instance="torus"/>
        </mesh>
    </asset>
    <option sdf_iterations="10" sdf_initpoints="40"/>

    <worldbody>
        <light name="top" pos="0 0 1"/>
        <body name="sphere" pos="1.0 0. 0." >
            <joint name="trans_1" type="slide" damping="100" axis="1 0 0"/>
            <joint name="trans_2" type="slide" damping="100" axis="0 1 0"/>
            <geom name="sphere_geom" type="sphere" size=".2 .2 .2" rgba="1 0 0 1" margin="1.0" gap="1.0"/>
        </body>

        <body name="sphere2" pos="0.0 1.0 0." >
            <geom name="sphere2_geom" type="sphere" size=".2 .2 .2" rgba="0 1 0 1" margin="1.0" gap="1.0"/>
        </body>

        <body name="torus" pos="0.0 0.0 0.0">
            <geom type="sdf" name="torus_geom" mesh="torus" rgba="0.4 0.4 0.4 1" margin="1.0" gap="1.0">
                <plugin instance="torus"/>
            </geom>
        </body>
    </worldbody>

    <actuator>
        <position name="trans_jnt_1" joint="trans_1" ctrlrange="-1 1" ctrllimited="true" kp="4000" kv="600"/>
        <position name="trans_jnt_2" joint="trans_2" ctrlrange="-1 1" ctrllimited="true" kp="4000" kv="600"/>
    </actuator>

    <sensor>
        <distance name="sphere_torus_distance_sensor" geom1="sphere_geom" geom2="torus_geom" cutoff="10"/>
        <distance name="sphere_sphere_distance_sensor" geom1="sphere_geom" geom2="sphere2_geom" cutoff="10"/>
    </sensor>
</mujoco>

You can see that the distance sensor reading between the mobile sphere and the sphere changes value as you slide the mobile sphere around. But the distance sensor reading between the torus (SDF) and the mobile sphere never changes unless the two geoms come into contact.
@dyackzan dyackzan added the enhancement New feature or request label Nov 6, 2024
@dyackzan dyackzan linked a pull request Nov 7, 2024 that will close this issue
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Enable distance sensing with SDF geoms PickNikRobotics/mujoco
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@dyackzan