In the previous issue of LP360 News, I introduced the use of Triangulated Irregular Networks (TIN) for modeling point derived elevation data as well as the basic concepts of “soft” breaklines. I realized when writing that first article that it is probably a useful exercise to review contours. Thus this part II article will be devoted to this subject and we will continue with breaklines in the third article of the series.
Before we delve in to hard breaklines, it is useful to review contours and how they are generated from a TIN. A contour is a mathematical concept. It is generally a curve along which a function of two variables has a constant value (also called an “isoline”). In terrain modeling, we can express the elevation, z, at any point (x, y) as a function of that planimetric location; z = f(x, y). Thus an elevation contour is a line in x, y along which the value of z remains a constant. If you walk along a contour line, you will never move up or down. In Figure 1 is illustrated a contour rendering (using dynamic contouring in LP360 for ArcGIS®) of an open pit mine. The 1,650’ contour is indicated by the red arrow. If you were to walk around this mine, staying on the contour (not recommended!), you would move in the x, y plane but not up or down.