Terrain Analysis and Visualization

1. Experiment name:

Terrain Analysis and Visualization

2. The purpose of the experiment:

Learn Terrain Analysis and 3D Terrain Visualization

3. Experimental content and requirements:

1. Terrain model extraction;

2. Terrain feature extraction;

3. Visual analysis;

4. 3D terrain visualization.

4. Experimental steps:

Experiment 1: Terrain Model Extraction

1. Open the DEM.tif file.

 

2. In Toolbox, start /Terrain/Topographic Modeling, in the Topo Model Input DEM dialog box, select the DEM.tif file, and then click OK to open the Topo Model Parameters dialog box.

 

3. In the Topo Model Parameters dialog, select 5 for the Topographic Kernel Size. Different transformation kernels can be used to extract multi-scale terrain information, and the larger the transformation kernel, the slower the processing speed.

4. Select the terrain model to compute by clicking in the "Select Topographic Measures to Compute" list.

5. If "Shaded Relief" is selected, enter or calculate the sun altitude and azimuth. Click the Compute Sun Elevation and Azimuth button, and in the Compute Sun Elevation and Azimuth dialog box, enter the date and time GMT as 9:0:0, Lat (latitude) as 40 degrees, and Lon (longitude) as 105 degrees. Click the OK button, ENVI will automatically calculate the sun altitude and azimuth.

6. Select the output path and file name, and click the OK button to execute the terrain model calculation.

 

7. The result is a multiband image file, with each terrain model forming a band.

 

8. Load different types of data in Data Manager.

 

Experiment 2: Terrain Feature Extraction

1. In Toolbox, start /Terrain/Topographic Features. In the Topographic Feature Input DEM dialog box, select the DEM.tif file, click OK, and open the Topographic Features Parameters dialog box. Some parameters need to be set.

2. Slope Tolerance (Slope Tolerance): 1. In degrees; Curvature Tolerance (Curvature Tolerance): 0.1. The two tolerances determine the classification of each feature. The slope value corresponding to the pixel divided into peak, pit, and pass must be smaller than the slope tolerance, and the curvature in the vertical direction must be greater than the curvature tolerance. Increasing the slope tolerance and decreasing the curvature tolerance increases the number of peak, pit, and pass divisions.

 

3. Topographic Kernel Size : 7.

4. Select all terrain features in the Select Feature to Classify list.

5. Select the output path and delivery name, and click OK to perform terrain feature extraction.

6. The result is a classified image of ENVI.

Experiment 3: Analysis of visual field

1. In Toolbox, start /Terrain/Viewshed Analysis Workflow, open the file selection panel File Selection;

2. Select the corresponding file DEM File: DEM.tif; Image File: Orthoimagery.tif, click Next to enter the Viewshed Analysis panel;

3. In the Viewshed Analysis panel, set the following parameters:

Visual distance Default View Range : 1000

Visual height Default View Height: 100

(4) The default state of the mouse is to draw "point annotation" to draw four points on the orthophoto;

 

(5) Select Any Source (the union of four observation points), check the Preview preview result, green indicates the visible area, and red indicates the invisible area;

 

(6) Select All Sources (the intersection of four observation points) respectively, and preview the results;

(7) Click Next to enter the Viewshed Export panel, and you can export the results of the line-of-sight analysis as vector and image results.

Experiment 4: 3D Terrain Visualization

1. Open Orthoimagery.tif and DEM data file DEM.tif respectively.

2. In the Toolbox, select /Terrain/3D SurfaceView. Select the three RGB bands of the Orthoimagery.tif image file, and then select the corresponding DEM.tif file.

 

3. In the 3D SurfaceView Input Parameters dialog box, some parameters need to be set.

 

4. Click the OK button to create a 3D scene.

 

5. Experimental experience:

    1. Question 1: "Shaded Relief" is selected when extracting the terrain model, and it is necessary to input or calculate the sun altitude and azimuth.

Solution: If "Shaded Relief" is selected, the sun altitude and azimuth need to be entered or calculated. Click the Compute Sun Elevation and Azimuth button, and in the Compute Sun Elevation and Azimuth dialog box, enter the date and time GMT as 9:0:0, Lat (latitude) as 40 degrees, and Lon (longitude) as 105 degrees. Click the OK button, ENVI will automatically calculate the sun altitude and azimuth.

2. Question 2: When visualizing 3D terrain, you need to select the three RGB bands of the Orthoimagery.tif image file, and then select the corresponding DEM.tif file.

3. Internship experience: learned DEM data and extracted geomorphic and topographic features from DEM. Learned the use of the viewshed analysis tool Viewshed Analysis Workflow. Learned simple 3D terrain visualization under ENVI. If you don't know the problem, you need to find more relevant steps and methods, and practice repeatedly.