Questions similar to this appear on the Be Communities. This question appeared in the MicroStation Forum.
Q
- What is a vertex?
- What is a segment?
- How do I count the vertices in a line?
- How do I count the segments in a line?
A A CAD tool, such as MicroStation, lets a user draw simple lines and line-strings, sometimes known as polylines. Lines and and line-strings are defined by points in 3D space. The points are termed vertices. Each pair of vertices is joined by a line segment.
Introduction to Line Geometry
Line
A simple line has a start point and end point: the vertices of the line. Those points are usually a 3D point that has X, Y and Z components. The start and end points are joined by a single segment. Here's an example of a simple line having a single segment …
A line is a line-string having only two vertices: the start and end points.
The line has two vertices and one segment.
Line-String
A line-string has a start point and end point and several intermediate vertices. Those points are usually a 3D point that has X, Y and Z components. Each pair of vertices is joined by a single segment. Here's an example of a line-string having several segments …
The line-string has four vertices and three segments.
Programming Lines with VBA
MicroStation VBA provides the LineElement object.
A LineElement has the usual MicroStation element characteristics, plus features relevant to a line or line-string.
For example, here's an abbreviated list of the methods and properties of a LineElement …
| Method | Comment |
|---|---|
LineElement.StartPoint | A Point3d |
LineElement.EndPoint | A Point3d |
LineElement.VerticesCount | Informs how many vertices make up this line or line-string. The number of segments is one less that the number of vertices |
LineElement.GetVertices | Returns the list of vertices. Each vertex is a Point3d |
To create a LineElement use application method CreateLineElement1 or CreateLineElement2.
For a full list of LineElement methods and properties, refer to
MicroStation VBA help.
Domain-Specific Terminology
Some technology domains, such as a Geographic Information System (GIS), call a vertex a node and a segment an edge.
Glossary
Vertex (plural Vertices)
A point at the start and end of a simple line or line-string, joined by one or more segments. A line-string will have multiple vertices: each pair of vertices is joined by a segment.
Segment
The part of a line that we see. It joins two vertices. A simple line has one segment. A line-string has multiple segments. The number of segments is one less than the number of vertices.
Questions
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