How infinite is an Infinite Plane?

I just created an IP for the first time, using the ThroughPoint option. Rhino generated a plane whose boundaries encompassed all the objects already in the viewport. It does not seem to be any different from creating a planar surface of like dimensions. If I add an object outside its boundary it will not split that object until I move or scale it to encompass the new object.

This seems to be a somewhat mean interpretation of infinite. Is this the expected behaviour or is it broken?

Rhino 7.18.22102.9001, 2022-04-12

Regards
Jeremy

Hi Jeremy - it

correct - pseudo infinite as the prompt says - it is just a quick way to do that. If you use IP inside a command, like Trim or Intersect, the plane is not created in the document, it is just used to trim, split, whatever and then disappears - that is the more common, I think, way to use infinite planes.

-Pascal

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Thanks @pascal. So just to be clear: In wirecut, say, when asked for the cutting object I should type IP, then select ThroughPoint, select my point, then select the object to be cut?

Hmm. Wirecut looks for a curve only I believe. But substitueTrim and what you suggest will work - ThroughPoint uses plane parallel to the current CPlane, but there are any number of other planes that can be specifed as well.

BooleanSplit will work as well, with IP, if you want ‘wirecut-like’ results.

-Pascal

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I think so too, but the help on IP lists wirecut as one of the commands it can be used with so I’ll have to try it out when back at my computer.

Certainly, thinking of the IP as a transitory thing makes more sense than keeping it as I initially thought.

That’s a Papercut then. Documentation is wrong: an IP cannot be used with Wirecut.

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Yes, Help is not super clear either on whether the object stays around or not. We’ll tune up, thanks.
RH-68378 Help: InfinitePlane tune up

-Pascal

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An infinite plane can be represented simply by the three coordinates of a point on the plane and the three components of a vector normal to the plane. This formulation for a infinite plane is actually simpler than is needed for a finite plane. It could be used for split, trim, etc operations but would require some rewrite of the code used in Rhino.

Hm. Not sure that I follow - Are you suggesting another way to designate a plane in the UI, with a point and a normal direction? I’m sure that is possible…

-Pascal

I was talking about how a truly infinite plane could be represented internally and used for calculations. I wouldn’t be surprised if some of the Rhino calculations involving planes use the point and normal formulation for intersections, etc because it can be computationally very efficient, and then follows with a separate calculation to trim the results to within the boundaries of the finite plane.

Lots of UI alternatives to input an infinte plane including:

Use selects a an existing plane or planar surface and Rhino uses that for the point and normal.

User provides a point on the plane another point in the direction normal to the plane. The normal vector is then the vector difference between the two points.

User provides three points on the plane. Rhino then uses first point as the point on plane and calculates the normal vector as a cross product using all three points.

User provides a point on the plane and selects one of the Cplane axis as the normal direction.

User provides a point on the plane and selects one of the Cplanes for the infinite plane to be parallel to.

Etc.