3D Analyst - Lab
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This document provides an overview of tools and techniques for 3D analysis in GIS, including interpolating surfaces from point data, creating contours and derivative surfaces, analyzing visibility, and comparing surfaces for cut-fill analysis. It discusses various interpolation methods like inverse distance weighting and spline that can be used to generate grid surfaces from point data. Methods for analyzing terrain properties like slope, aspect and hillshade are also covered. The document concludes with explanations of how to determine line of sight and create viewsheds for visibility analysis, as well as how to compare two surfaces to determine cut and fill volumes.
3D Analyst - Lab
- 1. (ITM 524) Practical Topic: 3D Analyst Laboratory - 1 “ Hartanto Sanjaya” <hartantosanjaya @ gmail.com>
- 2. 3D Analyst Activate 3D Analyst File Extensions 3D Analyst Set View Properties The projection for the view must be set to the projection of the raster or TIN data. Your feature theme data is projected to the coordinates your raster or TIN data is already in.
- 3. Working with Grid Theme Interpolate Grid Create Contours Derive Slope Derive Aspect Compute Hillshade
- 4. Interpolate Grid Interpolate Grid Using IDW Using Spline IDW Spline
- 5. The Inverse Distance Weighted (IDW) assumes that each input point has a local influence that diminishes with distance . It weights the points closer to the processing cell greater than those farther away. A specified number of points, or optionally all points within a specified radius, can be used to determine the output value for each location. Use it, for example, to interpolate a surface of consumer purchasing. More distant locations have less influence, because people are more likely to shop closer to home. The power parameter in the IDW interpolation controls the significance of the surrounding points upon the interpolated value. A higher power results in less influence from distant points. Each line in a barrier input line theme is used as a break that limits the search for input sample points. A line can represent a cliff, ridge, or some other interruption in a landscape. A choice of No Barriers will use all points specified in the No. of Neighbors or within the identified radius.
- 6. The Spline is a general purpose interpolation method that fits a minimum-curvature surface through the input points. Conceptually, it is like bending a sheet of rubber to pass through the points, while minimizing the total curvature of the surface. It fits a mathematical function to a specified number of nearest input points, while passing through the sample points. This method is best for gently varying surfaces such as elevation, water table heights, or pollution concentrations. It is not appropriate if there are large changes in the surface within a short horizontal distance, because it can overshoot estimated values. The Regularized method yields a smooth surface. The weight parameter defines the weight of the third derivatives of the surface in the curvature minimization expression. The Tension method tunes the stiffness of the surface according to the character of the modeled phenomenon. The weight parameter defines the weight of tension. The number of points parameter identifies the number of points per region used for local approximation.
- 8. Derive Slope
- 11. Working with TIN Theme Create TIN from Features Create Contours Derive Slope Derive Aspect Compute Hillshade Area and Volume Statistic
- 12. Create TIN from Features
- 13. Create Contours
- 14. Derive Slope
- 15. Derive Aspect
- 17. Area and Volume Statistic
- 18. Determining Cut and Fill Add the before and after surfaces as themes to a view or 3D scene. These surfaces can be two grid themes, two TIN themes, or a grid theme and a TIN theme. Activate both themes. Choose Cut Fill from the Surface menu. Using the dropdown list in the Cut Fill dialog, specify which surface is the before representation and press OK. 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.
- 19. Analyzing Visibility The two types of visibility analysis are line of sight and viewshed analysis. Determining line of sight Line of sight tells you whether a given target is visible from a particular point of observation. It answers the question, 'Can I see that from here?' Viewshed analysis Viewshed analysis identifies the areas on a surface that are visible from one or more observation points. It answers the question, 'What can I see from these locations?‘
- 20. ….. Hartanto Sanjaya Center of Technology for Natural Resources Inventory (PTISDA, BPPT) E-mail: hartantosanjaya @ gmail.com Web: http://hartanto.wordpress.com Y!M/GTalk: hartantosanjaya