Transform - Node Points

The Node Points operator for drawings creates a point object at the end of every line object. If the ends of several line objects coincide, only one node will be created at that location. This transform is used to build true networks out of systems of lines.

 

images\sc_add_node_points_01.gif

 

Suppose we have three lines that are incident to each other at a location. If we would like to treat these three lines as a network we need to create a point at the ends of the lines.

 

images\sc_add_node_points_02.gif

 

Applying Node Points creates a point at the end of each line. Only one point is created at the location where all three lines are incident to each other.

 

Note the difference between the Node Points and the Points transform.

 

images\sc_add_node_points_03.gif

 

Had we run the Points transform on the initial drawing we would have obtained the result above. The Points transform adds points at every coordinate location that defines the shape of the lines. The Node Points solver adds a point at only the terminal coordinate locations.

 

Nomenclature

 

Manifold can treat any system of lines and points as a network. When we discuss network subjects within Manifold, we shift terminology so that points are called nodes and lines are called links. People unfamiliar with networks will often refer to a system of lines such as that in the first illustration above as a "network." However, a network is defined by its nodes, not by its links. Links are simply a way of describing how the nodes of a network are formed into a network. If a drawing (or map) has no points, it is not a network.

 

Some GIS systems inaccurately use the word node to mean one of the coordinate locations that defines the shape of a polyline. That's a grave error since the world of networking (a considerably larger user population than GIS) in both computers and mathematics uses the word node to mean a point that is a vertex in a network.

 

Since GIS users will often wish to use a system of lines as a network even if it contains no nodes, Manifold takes a less strict view: default operators in Manifold will treat as a network any system of lines where the endpoints of the lines exactly coincide even if no points exist at the ends of the lines. Use the Node Points transform to add points to create a true network. This will avoid trouble with other software or scripts that may apply sophisticated network mathematics and insist that the "network" in use is a true network.

 

Tech Tip

 

Many transforms automatically run a Normalize Topology transform before running to eliminate common errors that may affect correct operation. The Boundaries , Points and Node Points transform operators do not normalize target objects before running. This makes it possible, for example, to segmentize lines with a length threshold of 10 meters, and then use the Points transform to place point objects at the locations of resulting inflection points.

 

See Also

 

About Networks