In the last edition of LP360 News, we discussed the creation of 3D breaklines. Recall that, for our purposes, a 3D breakline is a vector that has an elevation value (Z) associated with each vertex. Generally, 3D breaklines can be divided into two categories – those with the same elevation for each vertex (used for flat water bodies, for example) and those with the ability to store a different elevation value for each vertex (a down-stream flow polyline, for example).
In this edition, let’s look at a constant Z example such as a flat water body. A common method of collecting flat water bodies is to use heads-up digitizing from an orthophoto for the X, Y (planimetric) aspects of the construction and to store the desired (and single-valued) elevation in an attribute table. I like this storage approach as compared to using a pure 3D vector (where Z is stored on each vertex) since it saves 1/3 of the storage. Why store a Z value at each polygon vertex when all Zs are the same?