NRM 435 Spring 2016 ArcGIS 3D Analyst Page#1 of 9 0B3D Analyst Extension The 3D Analyst extension extends ArcGIS to support surface modeling and 3- dimensional visualization. 3D Shape Files Analogous to measures stored in PointM or PolylineM shapes, elevation or depths can be stored as an invisible Z measure for every point that makes up a point, line, or polygon theme. There are 2 basic ways to convert 2D features to 3D features. 1) By deriving feature elevation from a constant value or attribute value.
NRM 435 Spring 2016 ArcGIS 3D Analyst Page#2 of 9 2) By interpolating feature elevation from an elevation surface Sometimes you want see what the depth or elevation is within a the pointz, linez or polygonz feature.
NRM 435 Spring 2016 ArcGIS 3D Analyst Page#3 of 9 Triangulated Irregular Networks (TINs) A surface is either represented by an elevation grid or a Triangulated Irregular Network (TIN). A TIN is a network of triangles with each triangle having a slope gradient and direction. You can generate a TIN from a an elevation grid, point, line or polygon themes or 3-D shape files TINs have several advantages over elevation grids: 1) The surface model is more efficient and accurate because large triangles are produced for areas that have little terrain variation while many small triangles are produced to represent areas with high terrain variation. For example, take a LIDAR raster and convert it to a TIN Hillshade produced from elevation raster
NRM 435 Spring 2016 ArcGIS 3D Analyst Page#4 of 9 TIN produced from elevation raster One advantage ot TINs is relatively small file size compared to rasters: So in this example, the TIN is 73728/1980176 = 3.7 percent the size of the raster TIN Breaklines Breaks in terrain can be modeled by using point, line or polygon themes as breaklines. A hard breakline is where there is a sudden change in slope.examples might be a line theme of ridge roads, a line theme of streams, a polygon theme of lake shorelines, etc.
NRM 435 Spring 2016 ArcGIS 3D Analyst Page#5 of 9 Example TIN created using elevation raster and hard breaklines. Soft breaklines allow you to add edges to a TIN to capture linear features that do not alter the local slope of a surface. Study area boundaries could be included in a TIN as soft breaklines to capture their position without affecting the shape of the surface Other options for inputs when creating TINs include: Mass point - individual points are entered into the triangulation process as nodes to the triangulation. Examples include elevation estimates from GPS stations, contour lines, or marine soundings. Clip polygons define a boundary for interpolation. Input data that falls outside the clip polygon are excluded from the interpolation and analysis operations. Erase polygons are the opposite of clip polygons. All areas inside the polygon are marked as being outside the zone of interpolation. Analytic operations such as volume calculation, contouring, and interpolation will ignore these areas. Replace polygons set the boundary and all interior heights to the same value. Examples of replace polygons are lakes and ponds where the water level is a constant elevation. Fill polygons assign an integer attribute value to all triangles that fall within the fill polygon. The surface height is unaffected, and no clipping or erasing takes place. Once you have a TIN, you can do the following surface modeling operations: Add point, line, or polygon features to modify the TIN Create contours Estimate slope aspect, gradient Create a hillshade Create a viewshed Estimate areas and volume
NRM 435 Spring 2016 ArcGIS 3D Analyst Page#6 of 9 For example, what is the area above 870 meters elevation for the Murphy Dome area? Cut/Fill Analysis Cut-and-fill analysis determines how much material has been lost or gained in a study area by comparing two surface models of the area -- one before a change and one after. Therefore you need either two elevation grids or two TINs that represent the surface before and after a cut or fill
NRM 435 Spring 2016 ArcGIS 3D Analyst Page#7 of 9 ArcScene 3D Visualization In ArcGIS, ArcScene allows you to create 3-dimensional perspective views. You can drape point, line, polygon, grid, or image themes over a terrain model developed from an elevation grid or TIN. Here is an example of a the airphoto draped over the TIN. Here is an example, using the themes from the LIDAR lab. First create add your themes to your viewer then assign the canopy elevation values to each theme Since the X,Y units are in meters and the canopy units are in cm, assign a conversion factor of 100 so that the X,Y, Z values are all the same units.
NRM 435 Spring 2016 ArcGIS 3D Analyst Page#8 of 9 You can exaggerate the vertical dimension of your view.
NRM 435 Spring 2016 ArcGIS 3D Analyst Page#9 of 9 You can float point, lines or polygon themes above a surface. And you can extrude polygons above a surface.