QGIS/C4/DEM-Analysis/English-timed
From Script | Spoken-Tutorial
| Time | Narration |
| 00:01 | Welcome to this tutorial on DEM Analysis in QGIS. |
| 00:07 | In this tutorial, we will learn to, |
| 00:11 | Download DEM data from SRTM data website. |
| 00:16 | Show Hillshade of DEM. |
| 00:19 | Here I am using
Ubuntu Linux OS version 16.04 |
| 00:25 | QGIS version 2.18 and
A working internet connection. |
| 00:33 | To follow this tutorial you should be familiar with QGIS interface. |
| 00:39 | To view the prerequisite tutorials in this series, please visit this website. |
| 00:45 | Digital Elevation Model or DEM is a raster file. |
| 00:50 | It shows elevation data for each raster cell. |
| 00:55 | DEMs are used to represent the bare earth terrain. |
| 01:00 | The terrain is usually devoid of vegetation and man-made features. |
| 01:06 | DEMs are used for calculations and analysis of an area, based on the elevation. |
| 01:14 | Let us download DEM data. |
| 01:17 | Open the given link in any web browser. |
| 01:21 | Shuttle radar topography mission (SRTM) data website opens. |
| 01:27 | SRTM data from this website can be downloaded freely. |
| 01:32 | On the Download Manager page, the elevation models are arranged into tiles. |
| 01:39 | Two options for Tile Size and Format are available. |
| 01:44 | We can choose the tile size and format by clicking the radio buttons. |
| 01:50 | Scroll down the page to the world map. |
| 01:54 | Use + sign on the left corner of the map to zoom in the world map. |
| 02:00 | Click on Maharashtra tile. |
| 02:03 | Click on Search button located on the top-left corner of the world map. |
| 02:09 | Download window opens. |
| 02:12 | Scroll down to Description heading.
Click on Download SRTM link at the bottom. |
| 02:20 | A dialog-box opens, select Save File option. Click on OK button. |
| 02:29 | On my system, zip file downloads to the Downloads folder. |
| 02:34 | Extract the contents of the zip file. |
| 02:38 | Right-click and select Extract Here option. |
| 02:43 | Double-click on the extracted folder.
This is a DEM dataset. |
| 02:50 | Here we see many files with different file extensions. |
| 02:55 | Close the folder. |
| 02:57 | Open the QGIS interface. |
| 03:00 | Click on, Layer menu on the menu bar. |
| 03:04 | Select Add Layer, from the sub-menu, click on Add Raster Layer option. |
| 03:11 | Data source dialog-box opens. |
| 03:14 | Navigate to the SRTM folder downloaded from the SRTM website. |
| 03:21 | From the contents of the folder, select the file with .tif extension.
Click on Open button. |
| 03:31 | On the canvas you will see DEM of the terrain. |
| 03:36 | DEM contains all the 3D information about the terrain. |
| 03:41 | Each pixel on the raster image represents the average elevation at that location.
This elevation is given in meters. |
| 03:52 | Dark pixels represent areas with low altitude. |
| 03:57 | Lighter pixels represent areas with high altitude. |
| 04:02 | Let us begin the DEM analysis of this map. |
| 04:07 | Click on Raster menu on the menu bar. |
| 04:11 | Click on Analysis from drop down.
From the sub-menu click on DEM (Terrain models). |
| 04:19 | DEM dialog-box opens. |
| 04:22 | Input file field has DEM layer as the default selection. |
| 04:28 | Click on Select button next to Output file. |
| 04:33 | Save the results to.. Dialog-box opens. |
| 04:37 | In the dialog-box, name the file as Hillshade.tif. |
| 04:44 | I will save it on the Desktop. |
| 04:47 | Click on Save button. |
| 04:50 | Select Hillshade as Mode option. |
| 04:54 | Here by default Hillshade is already selected. |
| 04:59 | Check the check-box next to Load into canvas when finished. |
| 05:05 | Here by default it is already selected. |
| 05:09 | Leave the default settings as such. |
| 05:12 | Click on Ok button. |
| 05:15 | A pop-up box opens with message Processing Completed.
Click on OK button. |
| 05:22 | Click OK button in the Qgis.bin dialog-box. |
| 05:27 | Click on Close button on the DEM dialog-box. |
| 05:32 | A new layer, Hillshade is now added in the Layers panel. |
| 05:37 | On the canvas you will see a raster map in Hillshade mode. |
| 05:42 | This map is generated using light and shadow to create a 3D image. |
| 05:48 | To make the model more pronounced, we will use Hillshade as an overlay. |
| 05:54 | Now we will change the symbology of the original DEM layer. |
| 05:59 | Right-click on the srtm layer in the Layers Panel. |
| 06:04 | From the context menu select Properties option. |
| 06:09 | Layer Properties dialog-box opens. |
| 06:13 | Select Style from the left panel. |
| 06:17 | Under Band Rendering section, change the Render type to Singleband pseudocolor. |
| 06:24 | Under Load minimum/maximum values, click on minimum/maximum radio button. |
| 06:33 | Select Linear from Interpolation drop-down. |
| 06:37 | This is a default selection here.
From the Color drop-down select Spectral. |
| 06:44 | Scroll down.
Select Mode as Continuous from the drop down. |
| 06:50 | Click on Classify button. |
| 06:53 | 5 new color values are created. |
| 06:57 | The colors represent values of elevation of raster from lowest to highest. |
| 07:04 | Click on Apply button and OK button at the bottom right corner. |
| 07:10 | In the Layers panel, disable the Hillshade layer . |
| 07:14 | Uncheck the check-box against Hillshade layer. |
| 07:18 | Now on the canvas you will see a map in spectral colors. |
| 07:24 | The red shaded terrain is least elevated and blue is most elevated. |
| 07:30 | Enable the Hillshade layer. |
| 07:33 | Open the Layers Properties dialog-box. |
| 07:37 | Select Transparency from left panel. |
| 07:41 | Set the Global transparency to 50% by dragging the slider. |
| 07:47 | Click on Apply button and OK button. |
| 07:51 | Zoom in the map. |
| 07:53 | On the canvas now we see an enhanced topography of the landscape. |
| 08:00 | Let us summarize, |
| 08:03 | In this tutorial we have learnt to
Download DEM data from SRTM data website. |
| 08:11 | Show Hillshade of DEM. |
| 08:15 | Here is the assignment. |
| 08:17 | Visualize the terrain using Slope mode for the raster map. Change the symbology for the Slope layer |
| 08:27 | Hint: Select the Mode as Slope and use it as overlay. |
| 08:33 | Your completed assignment should look as shown here. |
| 08:38 | This video summarizes the Spoken Tutorial project. Please download and watch it. |
| 08:45 | We conduct workshops using Spoken Tutorials and give certificates.
Please contact us. |
| 08:54 | Please post your timed queries on this forum |
| 08:58 | The Spoken Tutorial Project is funded by NMEICT, MHRD Government of India. |
| 09:06 | This tutorial is contributed by Vaishnavi Honap from college of Engineering Pune,
Snehalatha Kaliappan and Himanshi Karwanje from IIT Bombay.Thank you for joining. |
