QGIS Raster Operations

Transcription

1 QGIS Raster Operations I) Raster Calculator II) Thematic Map Symbology III) Interpolation IV) Image Clipping V) Slope creation VI) Zonal statistics VII) Generating Contours VIII) Vector to Raster Conversion 1

2 Open QGIS I) Raster Calculator 1. Press Add Raster Layer icon 2. Access Liss3 data from \QGIS_Raster_Operations\L3Data\Hyd1DL3.img 3. Select projection EPSG:4326 from the Coordinate Reference System Selector window 4. Press OK and see the Multispectral image 2

3 5. Select and click from Raster Menu and view the following window 6. Select output file and write ( "Hyd1DL3@3" - "Hyd1DL3@2" ) / ( "Hyd1DL3@3" + "Hyd1DL3@2" ) in Raster Calculator Expression 3

4 7. Press OK to view the NDVI Image as shown below II) Thematic Map Symbology 1. Add NDVI Image either created or load from..\qgis_raster_operations\ndvi\ndvi.img 2. Right Click on Ndvi from layers window and select the Properties 4

5 3. Choose the following properties : Render Type Singleband pseudocolor Color Interpolation Discrete Spectral 11 for color map Mode- Equal Interval Classes Press Classify Button to view the following window 5

6 5. Press OK button to view the NDVI image with Symbology III) Interpolation 1. Add AWS data from..\qgis_raster_operations\aws_data\indiastns.shp 2. Select Interpolation command from Raster Menu 6

7 3. View the following window 4. Provide the following parameters Select ELEVATION for Interpolation attribute and press Add button See the default parameters for Interpolation method, Number of columns, Number of rows, cellsizex, Cellsize Y or provide the desire parameters. Provide the Output file See the following window. 7

8 5. Press OK and see the interpolated image in the main window. 8

9 IV) Image Clipping 1. Add DEM which is created in previous exercise or add form QGIS_Raster_Operations\IDW_Elevation\India_AWS_IDW_300.asc 2. Press Add vector icon from the toolbar 3. Access the polygon(ap State Boundary) from the path \QGIS_Raster_Operations\AP_Vectors\AP_State.shp 4. Press Open 5. Select Raster>Extraction>Clipper 9

10 6. Provide the outputfile 7. Select Mask radio button and view the following window 8. Press OK button to see the following window 10

11 V) Slope creation 1. Use AP_Elevation map from previous exercise or add from..\qgis_raster_operations\idw_elevation_ap\ap_elevation.tif 2. Select slope from Raster>Terrain Analysis>Slope as shown below 3. Provide the output file name in the following Window 4. Press OK button provide the symbology as given earlier exercise to see the following window 11

12 VI) Zonal statistics 1. Add the NDVI image created in earlier exercise or add from \QGIS_Raster_Operations\NDVI\ndvi.img 2. Add vector layer from \QGIS_Raster_Operations\AP_Vectors\Hyd_Poly.shp 3. Select zonal statistics from Raster>Zonal stistics>zonal statistics 4. See that the layers are automatically selected and Provide the column prefix as slope 5. Press OK 6. Select HYD_POLY and right click to select Open Attribute Table to see the following details 7. Observe that new three columns slopecount, slopesum, slopemean 12

13 VII) Generating Contours 1. Open a new project from by selecting icon 2. Add the DEM created from earlier exercise or add from \QGIS_Raster_Operations\IDW_Elevation\India_AWS_IDW_300.asc 3. Select Raster>Extraction>Contour as shown below 4. Provide output file name 5. Provide interval between contours as Select Attribute Name Checkbox and provide as Elev and see the window as given below 7. Press OK button 8. See the following window 13

14 9. Right Click on contour file and select Open Attribute Table to see the elevation values as shown below 14

15 VIII) Vector to Raster Conversion 1. Open new project 2. Add Hyd_Poly from the path \QGIS_Raster_Operations\AP_Vectors\Hyd_Poly.shp 3. Select Raster>Conversion>Rasterize(Vector to Raster) as shown below 4. See that Input file already selected and Provide output file for rasterized vectors (raster) and Raster size in pixels as 300 in each Widht and Height 5. Press OK see the raster as given below 15

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