In that case, the engineer was probably trying to make aesthetically pleasing contours that don’t reflect the actual CAD model that s/he created. Suppose you see nice-looking curving contours that don’t hit any of your spot elevations or that cause flags in your breaklines. If you ever see jagged or zigzagging contours, that means that the engineer probably used a poor-quality surface to generate the contours. This method can be good or bad depending on the quality of the surface they made. Some engineers build the DSM and then generate contours that directly trace that surface. CONTOUR LINES TO DETERMINE BREAKLINES?Ĭontour lines can be molded differently in CAD, depending on the engineer. Breaklines are critical to creating an accurate surface model because it is not enough to have just the data alone it is the interpolation of that data that gives you the model's shape. This line data forces the surface to create triangles that connect the vertices on the breakline. They are lines used to connect data representing a specific surface, such as the centerline of a road, a ridgeline, or a ditch's flowline. For example, spot elevation points tell you the elevation of various drainage features and give you the top and bottom of retaining walls, among other things.īreaklines are a way of manipulating the surface triangles. These points are critical for construction because they provide you with specific locations above or below their surroundings. Spot elevations tell you the actual elevation of a particular point, both existing and proposed, which can be used for planning purposes and for creating 3D models. Precise grading plans will provide you with better drainage management, accurate building foundation depths, and they will also account for the various landscaping features.Ī spot elevation is a point on a map that identifies the height above mean sea level. Some reasons for this are: it will help you get your permits easier, and it allows your earthwork contractors to provide you with better estimates. When it comes to grading plans, the quality of the plan is the key factor. For this reason, topographic maps are made up of different line types, colors, and shadings, which give you a visual of the changes in elevation and terrain shape. These models are used for creating topographic maps.Ĭreating, or even reading, topographic maps can be overwhelming because we live in a 3D world, and it's not necessarily easy to represent it all on a 2D map. The difference between the DSM and the DTM is that the DSM includes all objects on the earth's surface, whereas a DTM represents only the bare ground. These models provide a 3D representation of terrain elevation data. A Triangulated Irregular Networks (TIN) is a representation of a continuous surface consisting entirely of triangular facets. A Digital Elevation Model (DEM) is often used as a generic term for Digital Surface Models (DSMs) and Digital Terrain Models (DTMs). So, we will start with defining DEMs, DSMs, DTMs and TINs. We can't jump right into answering that question without providing you with some terms related to this topic that are important for you to know. We are often confronted with that question and are here to help you figure it out. Are you having trouble deciding when to use spot elevations versus contour lines to determine your breaklines? Well, don't worry because you're not alone.
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