Bottom of a cuboid

Revit
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1

I’m trying to place an object at the bottom of a cuboid, but I don’t know how. I manage to put it at the top and in the center, but don’t seem to find a way to put it at the bottom… Does anyone know how?

2

Construct a point as follows:

X value = (Minimum Point X value + Maximum point X value) /2
Y value = (Minimum Point Y value + Maximum point Y value) /2
Z value = Minimum Point Z value

That will be bottom center of the cuboid.

You can also use this method with the min/max point of a bounding box around any object, technically.

3

I’m not sure i follow how to connect the nodes (I’m new to Dynamo). This is the script I made earlier about putting an object at roof height.

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4

Assuming your cuboid is aligned to the world axes (at least on the XY plane), then you’ll have 4 points that makeup the bottom surface. Get the 4 corner points with the lowest Z value and get the average of the points.

For a generic case that looks at any surface alignment, check out this recent thread:
Cannot get base of all generic masses - Revit - Dynamo

5
  • Geometry.Explode will convert the solid cuboid into a list of surfaces.
  • Surface.NormalAtParameter with U and V parameters of 0.5 will give you the normal at the center of each surface.
  • Vector.Z will give you the Z component of those vectors. This will be a value between -1 (the surface is facing down and therefore the bottom) and 1 (the surface is facing up and therefore the top), where values of zero are vertical (the surfaces are facing out and therefore are sides)
  • List.SortByKey will now allow you to sort the list of surfaces (from the Geometry.Explode node) by the key of the respective Z component of their normal. Be sure to use @L2 for both inputs.
  • List.FirstItem will give you the surface which had the lowest Z component on it’s normal.
  • Surface.PointAtParameter will now allow you to select a point on that face which you can use to create a family instance (what I think you mean for placing an object), or a Surface.CoordianteSystemAtParameter can get a coordinate system if you want to position a curve relative to the surface’s orientation, or a Curve.ByParameterLineOnSurface node can produce a line relative to the surface, or… you have lots of options now.
6

You can get the bottom surface using a one liner in a python node

OUT = filter(lambda surface: surface.NormalAtParameter().Z == -1, IN[0].Explode())

Edit - Jacob’s method (most facing down normal)

OUT = sorted(IN[0].Explode(), key=lambda surface: surface.NormalAtParameter().Z)[0]
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