#A CONTOUR DRAWING PROFESSIONAL#

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#A CONTOUR DRAWING PROFESSIONAL#

Penn State Professional Masters Degree in GIS: Winner of the 2009 Sloan Consortium award for Most Outstanding Online Program Dutton e-Education Institute College of Earth and Mineral Sciences, The Pennsylvania State University. Dutton e-Education Institute and Assistant Program Manager for Online Geospatial Education, and Adrienne Goldsberry, Senior Lecturer, John A. Dutton e-Education Institute, Beth King, Senior Lecturer, John A. Dutton e-Education Institute Ryan Baxter, Senior Research Assistant, John A. Instructors and contributors: Jim Sloan, Senior Lecturer, John A. Dutton e-Education Institute, and Director of Education, Industry Solutions, Esri. The distinguishing geometric characteristic of a Delaunay triangulation is that a circle surrounding each triangle side does not contain any other vertex.)Īuthor: David DiBiase, Senior Lecturer, John A. One approach is called Delaunay Triangulation which, in one of its constrained forms, is useful for representing terrain surfaces. (There are algorithms for triangulating irregular arrays that produce unique solutions. Similarly, the smaller the contour interval you intend to use, the more spot elevations you need. In general, the density of spot elevations should be greater where terrain elevations vary greatly, and sparser where the terrain varies subtly.

Related to this element of subjectivity is the fact that the fidelity of a contour map depends in large part on the distribution of spot elevations on which it is based. As you will see, deciding which spot elevations are 'near neighbors' and which are not is subjective in some cases. You may notice that there is more than one correct way to draw the TIN. I omitted breaklines from this example just to make a point. Photogrammetrists refer to spot elevations collected along linear features as breaklines (Maune, 2007). In practice, spot elevations would always be measured at several points along the stream, and along ridges as well. Wonder why I suggest that you not let triangle sides that make up the TIN cross the stream? Well, if you did, the stream would appear to run along the side of a hill, instead of down a valley as it should. With a little imagination and practice, you can visualize the underlying surface from the TIN even without drawing contours. (Spot elevations produced photogrammetrically are called mass points.) A useful characteristic of TINs is that each triangular facet has a single slope degree and direction. The vertices of the triangles are spot elevations that may have been measured in the field by leveling, or in a photogrammetrist's workshop with a stereoplotter, or by other means. A TIN is a vector representation of a continuous surface that consists entirely of triangular facets. The result is a triangulated irregular network (TIN).

A contour drawing