GIS basic software and operation (vii)

Original GIS basic software and operation (vii)

Practice VII, Topography analysis

Terrain Analysis: Generation and application of tin and DEM

1. Deepen the understanding of the principle and method of tin establishment process;
2. Master the technical method of establishing DEM and tin in ArcGIS;
3. The ability of using DEM to solve geo-spatial analysis problem is mastered.

1. TIN and DEM Generation

Vector data:

• Elevation Point elevpt_clip.shp

• Elevation elev_clip.shp

• Boundary boundary.shp

• Erhai erhai.shp

Most of the exercises in this chapter will use the three-dimensional analysis extension module, to use the "three-dimensional analysis module" first in ArcMap to execute the menu command "Custom" > "Extension Module", in the Extension Module Management window, check the "3D
Analyst ". Then in ArcMap
Right-click on the blank area of the toolbar and find "3D" in the right-click menu that appears.
Analyst item, click the item to display the three-dimensional Analysis toolbar in ArcMap.

1.1 Generating a tin from elevation point, contour vector data to Dem

(1) Create a new map document in ArcMap to add vector data: Elevpt_clip, Elev_clip, boundary, Erhai;

(2) in Arctoolbox, double-click 3D Analyst Tools > Tin management > Create tin to open the Create Tin dialog box;

(3) Add the above 4 layers in the dialog box, parameter settings such as (note: When building the Erhai layer, the Sf_type parameter needs to be set to "hard Replace"):

Parameter description in the Create Tin dialog box:

Height_field: elevation field, which provides elevation values for features. When there is no height attribute in the layer, the <None> is optional, but at least one of the layer attribute tables is guaranteed to have an elevation value.

sf_type: surface feature Type field, which defines how feature geometry is added to the triangle.

Tag_field: A label field that specifies the attribute field of the feature type that is used as the label value in the tin.

The "Sf_type" field value type description:

discrete multipoint: is the node in the Tin network, mainly determines the shape of the surface, in the area with a greater degree of surface changes include more discrete points, less surface changes in areas including fewer discrete points.

break line: mainly used to indicate natural features (such as ridges, rivers) or artificial features (such as roads), broken down and soft break.

hard break: used to denote discontinuities in slope, such as rivers and roads, which can be included as hard break lines in tins;

soft break: used to add edges to a tin to capture linear features that do not alter the local slope of the surface, and the study area boundary can be included as a soft break line in a tin.

(1) in layer control, only [Erhai] and [tin] two layers are turned on, and the edge type of the layer [tin] is turned off, which results in the following:

(1) in Arctoolbox, double-click 3D Analyst Tools > turn from Tin > tin to Raster to open the tin to Raster dialog box and set the relevant parameters in the dialog box (as shown):

Need to be saved in the personal database

(1) Determine the resulting raster data layer [Tingrid], where each raster cell represents an area of 50m*50m, as shown in.

Display of 1.2 tin

(1) in layer control, open the [Tin] layer only, edit the properties of the layer, in the Properties dialog box, click on the Symbology Options page, remove the "Edge type" and "Elevation" check, and click the "Add" button as shown:

(1) In the Add Renderer dialog box, add edges with the same symbol and nodes with the same symbol to the display list of the tin, as shown in:

(1) Click OK to enlarge the [tin] layer locally, carefully understand the storage mode and display mode of the tin, as shown in:

1.3 Converting a tin to a slope polygon

(1) Create a new map document, load the layer [Tin], refer to the previous action, add the "surface slope with graduated color ramp" item to the display list of the Tin;

{width= "3.248031496062992in"
Height= "2.688976377952756in"}

(1) In the dialog box above, select Slope (degrees), specify "class" in category as "5", click the "Classify" button, and in the box below, specify "method" in "Classification" as "manual", and in the Break Value list, enter the slope break value in turn: 8, 15, 25, 35, 90, as shown in:

When you click OK to close the Layer Properties dialog box, the layer [Tin] renders according to the specified rendering, as shown in the following:

(1) in Arctoolbox, double-click 3D Analyst Tools > Surface triangulation > Surface slope to open the Surface Slope dialog box and specify the parameters as shown (note: You need to select a database Slopecode.mdb in the class schedule) :

Get the polygon layer [Tinslope], which represents the distribution of various slopes in the study area, the result is a vector format, open its attribute table can see the attribute field [Slopecode]
The values are 1, 2, 3, 4, 5.

View vector layers: tinslopef
In the feature attribute table, where the attribute fields [Slopecode]1, 2, 3, 4, 5 represent slope ranges (0-8), (8-15), (15-25), (25-35), (35-90), respectively.
。

1.4 Merging broken polygons

(1) Create a new map document, load the slope polygon layer generated in the previous step [Tinslope], open the attribute table, add a field area (type Double);

(1) Calculate the area of each polygon by using the Calculate geometry operation:

(1) Execute the menu command "select" > "Select by Attribute", open the "Select by Attribute" dialog box, select the polygons with a size of less than or equal to 10000 square meters, and the selected polygons will be highlighted:

(1) Double-click data management Tools > Cartographic synthesis > Dismiss in Arctoolbox to open the dismiss dialog to merge polygons with an area of less than or equal to 10000 square meters into the largest polygon in the surrounding area.

Original polygon

Merged polygons

Enlarge the map appropriately, comparing the original layer [Tinslope] with the merged layer [tinslope_eliminate].

Eliminate (combined broken polygon) operating principle

Convert 1.5 tin to aspect polygon

Refer to the steps in section 1.3 to get the aspect polygon layer [Tinaspect]:

The resulting value of the attribute Aspectcode in the slope Polygon ( -1,1,2,3,4,5,6,7,8,9) represents the aspect of the current pattern (flat, north, northeast, east, southeast, south, southwest, west, northwest, north), of which 1,
9 are the same can be combined into 1.

2. Application of DEM 2.1 slope slope

(1) Create a new map document and load the raster data obtained in the 6th step of the 1.1 section [Tingrid];

(2) Double-click Spatial Analyst Tools > Surface Analysis > Slope in arctoolbox to open the Slope dialog box, referencing the specified parameters:

(3) to get the slope raster Slope_tingrid, the value of the grid cell varies between [0-90] degrees:

(1) Right-click on the layer [Slope_tingrid], execute [Properties command], set layer [symbol], readjust slope grade (refer to section 2nd of 1.3 for classification):

2.2 Slope direction Aspect

(1) Create a new map document and load the raster data obtained in the 6th step of the 1.1 section [Tingrid];

(2) Double-click Spatial Analyst Tools > Surface analysis > Aspect in Arctoolbox to open the Aspect dialog box, referencing the specified parameters:

(1) Get the Poe grid [Aspecttingrid]:

2.3 Extracting Contour Lines

(1) Create a new map document and load raster data [Tingrid];

(2) Double-click 3D Analyst Tools > Raster surface > Contour in Arctoolbox to open the Contour dialog box and refer to the specified parameters:

(1) Generate contour vector layer [Contour_tingrid]:

2.4 Calculating the shadow map of the terrain surface

(1) Create a new map document and load raster data [Tingrid];

(2) Double-click 3D Analyst Tools > Raster surface > Hillshade in Arctoolbox to open the Hillshade dialog box and refer to the specified parameters:

(1) Generate a grid of ground shadows: [Shadowtingrid]:

(1) Close all layers except [Tingrid] and [Shadowtingrid] and place [Tingrid] above [Shadowtingrid], right click [Tingrid], execute "Properties" in the right-click menu that appears, in the "Layer properties" dialog box, set the color in the Symbology Options page as shown in the reference:

(1) Open the toolbar "effects", as shown in, set the transparency of the raster layer [Tingrid] to about 40%, so that the underlying hillshade effect is partially revealed.

2.5 Visual analysis

(1) Create a new map document and load raster data [Tingrid];

(2) Open the "3DAnalyst" toolbar and select the "Create Line of sight" tool from the toolbar:

(1) in the "line of Sight" dialog box that appears, enter "Observer offset" and "target offset", which is the distance from the ground,

When you draw multiple lines in different directions from a point A in the map display area, you can get the visibility of the observer point A to the different target points:

The green segment represents the visible part, and the red segment represents the invisible part

2.6 viewshed Analysis

(1) Create a new map document, load raster data [Tingrid] and vector data [mobile base station. SHP];

(2) Double-click 3D Analyst Tools > Visibility > viewshed in Arctoolbox to open the Viewshed dialog box and refer to the parameters specified:

(1) Generate a visual area grid [View_tingrid], where green indicates that the existing transmit base station information has been covered area, the red color indicates that the cell phone signal can not receive the area.

2.7 Terrain Profile

(1) Create a new map document and load raster data [Tingrid];

(2) Open the 3DAnalyst toolbar and select the line interpolation tool from the toolbar to track a line segment that can get the elevation value from [Tingrid]:

(1) Select the Create Profile View tool from the 3DAnalyst toolbar to get a section view of the area where the segment is located:

Wang Smooth
Comment posted: 2016-01-14 14:56:18
Updated on: 2016-04-28 21:41:49
Original link: Http://www.wshunli.com/2016/01/14/GIS basic software and operation-Seven/
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GIS basic software and operation (vii)