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Why are operators Object -> Set Origin -> "Origin to Geometry" and Object -> Set Origin -> "Origin to center of Mass (Volume)" allocating Origin differently? I would imagine them finding center of Geometry and simply putting Origin there. What is the difference? Object -> Set Origin -> "Origin to Geometry

Object -> Set Origin -> "Origin to center of Mass (Volume)

Blue line is the location of origin set by Object -> Set Origin -> "Origin to Geometry" operator. Red line is the location of origin set by Object -> Set Origin -> "Origin to center of Mass (Volume)" operator.

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    $\begingroup$ Origin to Geometry will take the vertices density into account, while Origin to Mass will take the general shape of the volume only into account $\endgroup$
    – moonboots
    Commented Apr 30, 2023 at 6:48

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If additional information was needed:

Origin to geometry

It is the mean of the vertices coordinates.

Origin to center of mass (surface)

Calculates the centroid of each face then the barycenter of these centroids ponderated by the face surfaces.

A link.

An illustration:

enter image description here

For each face, loops over its triangles (green, blue, red), calculates their centered and ponderate them by the triangle surface. In result, calculates the yellow one (their barycenter).

Do that for all faces and calculate the overall barycenter.

Origin to center of mass (volume)

Calculates the centroid of each volume (see below) then the barycenter of them ponderated by their individual volumes.

A volume here is made of a tetrahedron composed of each face triangle and a reference center.

This center is itself precalculated as a barycenter of each face centroid ponderated by their amount of vertices.

A link.

An illustration:

enter image description here

For each face and from the center calculates the volume for each tetrahedron (green, blue, red) and the volume center is the barycenter. Do it for all faces and get the barycenter off all (ponderated by individual volumes).

The difference between the two former is often small, but that may be important for simulations.

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  • $\begingroup$ So, basically, Origin to Geometry accounts only for the vertices shown in edit mode, and Origin to Center of Mass (Volume/Surface) takes in account the whole Volume/Surface Area of a shape? I still kind of don't get your "Origin to Center of Mass (Volume)" explanation. It seems to me like you described "Origin to Center of Mass (Surface)" again. I very much might be wrong. $\endgroup$
    – Imp
    Commented May 1, 2023 at 10:10
  • $\begingroup$ @Imp, I've added some illustration. A bit hard to describe as my english is far from perfect... $\endgroup$
    – lemon
    Commented May 1, 2023 at 10:40
  • $\begingroup$ I kind of understand what you're trying to say. However, on the first picture you've provided, I think that the "yellow barycenter" should be closer to the red centroid, shouldn't it? That is because Blender calculates a mean out of those centroids' positions and, therefore, we get the barycenter. Correct me if I'm wrong, please. $\endgroup$
    – Imp
    Commented May 1, 2023 at 13:35
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    $\begingroup$ Yes the yellow are rapidly drawn for illustration, not real things. And yes, this is the principle. $\endgroup$
    – lemon
    Commented May 1, 2023 at 13:40
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Origin to Geometry (1) will take the vertices density into account, while Origin to Center of Mass (2) will take the general shape of the volume only into account, therefore the difference:

enter image description here

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