Create a Solid of Rotation using MicroStation VBA

Questions similar to these appear in the Be Communities MicroStation Programming Forum.

This page lists some solutions to common MicroStation VBA (MVBA) problems. Tips are published as examples and are not necessarily working code.

SmartSolids

Bentley Systems add the SmartSolid class to MicroStation VBA in a late version of MicroStation V8i. It continues to be available with MicroStation CONNECT. There are two related classes. The comments are taken from MicroStation VBA help …

SmartSolid: Holds generic methods useful in dealing with SmartSolid objects
SmartSolidElement: A kind of Element that corresponds to a MicroStation SmartSolid/SmartSurface element

In other words, the SmartSolid class is an implementation of mathematical concepts that help us create and manipulate 3D solid objects. The SmartSolidElement class provide tools to handle a 3D solid as a MicroStation DGN element.

Solid of Rotation

We can create a solid of rotation by first identifying or creating a 2D profile. Next, we rotate the profile about a given point, in a given orientation, by a specified angle. The VBA method is SmartSolid.RevolveProfile.

2D Profile

Look at the VBA documentation for SmartSolid.RevolveProfile: Revolves a wire or sheet body about the axis passing through the point and along the axis.

The profile element is a DGN element: profile body which is swept along the path, it should not be a closed curve.

A profile is a two-dimensional open shape. You can create such an element from a simple line-string or other primitive curve, or a complex string. Here's an example …

Dim profileElements(3) As ChainableElement

Set profileElements(0) = CreateLineElement2(Nothing, Point3dFromXYZ(0.0591, 0.0245, 0), Point3dFromXYZ(0.0836, 0.0806, 0))
Set profileElements(1) = CreateLineElement2(Nothing, Point3dFromXYZ(0.0836, 0.0806, 0), Point3dFromXYZ(0.0899, 0.0792, 0))
Set profileElements(2) = CreateLineElement2(Nothing, Point3dFromXYZ(0.0899, 0.0792, 0), Point3dFromXYZ(0.0899, 0.0203, 0))
Set profileElements(3) = CreateLineElement2(Nothing, Point3dFromXYZ(0.0899, 0.0203, 0), Point3dFromXYZ(0.0591, 0.0245, 0))

Dim oProfile As ComplexStringElement
Set oProfile = CreateComplexStringElement1(profileElements())

Rotation Parameters

Next, decide how to rotate that profile. We need a point to rotate about, an axis of rotation, and a rotation angle (the angle, as is usual, is measured in Radians) …

Dim pointOfRotation As Point3d
pointOfRotation = Point3dZero

Dim xAxis As Vector3d
'  Rotate about the X-axis
xAxis = Vector3dFromXYZ(1, 0, 0)

Dim rotateAngle As Double
'  Rotate by Pi radians (180°)
rotateAngle = Pi

Rotate Profile

Now everything is ready. We're going to create a SmartSolidElement that can be added to a DGN model. We create that SmartSolidElement using the RevolveProfile method of class SmartSolid. The actual rotation is quite simple …

Dim oBodySolid As SmartSolidElement
Set oBodySolid = SmartSolid.RevolveProfile(oProfile, pointOfRotation, xAxis, rotateAngle)

Cap Surface

Finally, you may want to call SmartSolidElement.CapSurface. That ensures that you create a 3D solid rather than a 3D surface. Or, as VBA help puts it: Converts a sheet body to a solid by adding faces to fill up "hollow spaces".

oBodySolid.CapSurface
ActiveModelReference.AddElement oBodySolid

Here's a screenshot of the resulting solid …

Problems

Some people have reported problems using SmartSolidElement.RevolveProfile. Here are some comments …

The profile of rotation must be an open element. It should not be a closed shape
The angle of rotation is specified in radians, not degrees. Note that if you intend to rotate by, say, 180° and specify 180 for the rotation, that is about 10313°, which is quite a few rotations and probably not what you intended. VBA provides a conversion function Radians(), so you've no excuse for not using radians
The axis of rotation is define by a vector. If you want to rotate about the Z axis that vector is 0,0,1 (the example above rotates about the X axis)
The origin and range of the resulting solid must conform to MicroStation's rules for solids, in particular the solid working area

MicroStation VBA developer Paul Rowlands commented, after struggling with SmartSolidElement.RevolveProfile: Cause of the problem is global origins set at large values which a certain infrastructure client likes to use in their seed files

Questions

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