Difference between revisions of "QGIS/C4/DEM-Analysis/English"

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To view the prerequisite tutorials in this series, please visit this website.
 
To view the prerequisite tutorials in this series, please visit this website.
 
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'''DEMs''' are used for calculations and analysis of an area, based on the elevation.
 
'''DEMs''' are used for calculations and analysis of an area, based on the elevation.
 
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'''STRM website'''
 
'''STRM website'''
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Input file field has '''DEM layer '''as the default selection.
 
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'''Summary'''
 
'''Summary'''
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'''Assignment 1'''
 
'''Assignment 1'''
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'''Spoken Tutorial Workshops'''
 
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'''Forum for Specific questions'''
 
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'''Acknowledgements'''
 
'''Acknowledgements'''

Latest revision as of 16:56, 2 December 2019

Visual Cue Narration
Slide Number 1

Title Slide

Welcome to this tutorial on DEM Analysis in QGIS.
Slide Number 2

Learning Objectives

In this tutorial, we will learn to,
  • Download DEM data from SRTM data website.
  • Show Hillshade of DEM.


Slide Number 3

System Requirement

Here I am using

Ubuntu Linux OS version 16.04

QGIS version 2.18 and

A working internet connection.

Slide Number 4

Pre-requisites

To follow this tutorial you should be familiar with QGIS interface.

To view the prerequisite tutorials in this series, please visit this website.

Slide Number 5

About DEM

Digital Elevation Model or DEM is a raster file.

It shows elevation data for each raster cell.

Digital Elevation Model or DEM is a raster file.

It shows elevation data for each raster cell.

Slide number 6

About DEM

DEMs are used to represent the bare earth terrain.

The terrain is usually devoid of vegetation and man-made features.

DEMs are used for calculations and analysis of an area, based on the elevation.

Slide number 7

STRM website

Open Firefox/Chrome web browser.

Type http://srtm.csi.cgiar.org/srtmdata/

Let us download DEM data.

Open the given link in any web browser.

http://srtm.csi.cgiar.org/srtmdata

Cursor on SRTM data website.

Click on SRTM data tab on top-left corner of the page.

Shuttle radar topography mission (SRTM) data website opens.

SRTM data from this website can be downloaded freely.

Cursor on the Download Manager page.


Point to Tile Size and Format.

Point to radio button.

On the Download Manager page, the elevation models are arranged into tiles.

Two options for Tile Size and Format are available.

We can choose the tile size and format by clicking the radio buttons.

Scroll down Scroll down the page to the world map.
Cursor on +/- sign on the map. Use + sign on the left corner of the map to zoom in the world map.
Click on the Maharashtra tile. Click on Maharashtra tile.


Click on Search. Click on Search button located on the top-left corner of the world map.
Cursor on Download window. Download window opens.
Scroll down.

Click on Download SRTM.

Scroll down to Description heading.

Click on Download SRTM link at the bottom.

A dialog-box opens, select Save File option. Click on OK button. A dialog-box opens, select Save File option. Click on OK button.
Open Downloads folder and point the zip file. (STRM 51_09) On my system, zip file downloads to the Downloads folder.
Right-click to extract the contents. Extract the contents of the zip file.

Right-click and select Extract Here option.

Double-click to open the folder.

Cursor on

Double-click on the extracted folder.

This is a DEM dataset.

Here we see many files with different file extensions.

Click on close button on the top-left corner. Close the folder.
Double-click on QGIS icon. Open the QGIS interface.
Click on layer on the menu bar.

Click on add layer.

Click on add Raster layer.

Click on, Layer menu on the menu bar.

Select Add Layer, from the sub-menu, click on Add Raster Layer option.

Point to Data source manager Raster dialog-box . Data source dialog-box opens.
Click on Browse.

Locate the SRTM folder.

Navigate to the SRTM folder downloaded from the SRTM website.
From the folder, select the file srtm_53_11.tif

Click Open button.

From the contents of the folder, select the file with .tif extension.

Click on Open button.

Point to the DEM on canvas. On the canvas you will see DEM of the terrain.


DEM contains all the 3D information about the terrain.

Point to the DEM on canvas.

Scroll to zoom in.

Each pixel on the raster image represents the average elevation at that location.

This elevation is given in meters.

Point to the DEM on canvas. Dark pixels represent areas with low altitude.

Lighter pixels represent areas with high altitude.

Cursor on canvas Let us begin the DEM analysis of this map.
Click on the menu item Raster.

Select Analysis from drop down.

Select DEM (Terrain models).

Click on Raster menu on the menu bar.

Click on Analysis from drop down.

From the sub-menu click on DEM (Terrain models).

DEM (Terrain models) dialog-box opens. DEM dialog-box opens.

Input file field has DEM layer as the default selection.

Click on Select in front the Output file. Click on Select button next to Output file.
Select the raster file to save the results to Dialog-box opens. Save the results to.. Dialog-box opens.
In the File name text box, type Hillshade.tif .

Click on Save.

In the dialog-box, name the file as Hillshade.tif.

I will save it on the Desktop.

Click on Save button.

Cursor on DEM (Terrain models) dialog-box. Select Hillshade as Mode option.

Here by default Hillshade is already selected.

Check the box next to Load into canvas when finished. Check the check-box next to Load into canvas when finished.

Here by default it is already selected.

Leave the default settings as such.

Click on Ok Click on Ok button.
Finished dialog-box opens.

Click on Ok.

A pop-up box opens with message Processing Completed.

Click on OK button.

Click OK button in the Qgis.bin dialog-box. Click OK button in the Qgis.bin dialog-box.
Click on Close in DEM (Terrain models) dialog-box. Click on Close button on the DEM dialog-box.
Cursor on layers panel. A new layer, Hillshade is now added in the Layers panel.

On the canvas you will see a raster map in Hillshade mode.

Cursor on canvas. This map is generated using light and shadow to create a 3D image.
Cursor on Hillshade layer. To make the model more pronounced, we will use Hillshade as an overlay.
Cursor on canvas. Now we will change the symbology of the original DEM layer.
Right-click on the srtm_53_11 layer in the Layers Panel.

Select Properties option.

Right-click on the srtm layer in the Layers Panel.

From the context menu select Properties option.

Cursor on Layer Properties dialog-box. Layer Properties dialog-box opens.
Select Style from left panel. Select Style from the left panel.
Click on Singleband pseudocolor in front of Render type. Under Band Rendering section, change the Render type to Singleband pseudocolor.
Under Load min/max values, click on min/max. Under Load minimum/maximum values, click on minimum/maximum radio button.
Scroll down.

Select linear Interpolation.

Choose Spectral.

Select Linear from Interpolation drop-down.

This is a default selection here.

From the Color drop-down select Spectral.

Select Mode as Continuous.

Click on Classify button.

Scroll down.


Select Mode as Continuous from the drop down.

Click on Classify button.

Cursor on the panel. 5 new color values are created.

The colors represent values of elevation of raster from lowest to highest.

Click on OK button. Click on Apply button and OK button at the bottom right corner.
In the Layers panel,

Uncheck the check-box for Hillshade layer.

In the Layers panel, disable the Hillshade layer .

Uncheck the check-box against Hillshade layer.

Point to the map. Now on the canvas you will see a map in spectral colors.
Cursor on the panel. The red shaded terrain is least elevated and blue is most elevated.

Enable the Hillshade layer.

Right-click on the Hillshade layer in the Layers Panel.

Select Properties option.

Open the Layers Properties dialog-box.
Select Transparency from left panel. Select Transparency from left panel.
Set the Global transparency to 50%. Set the Global transparency to 50% by dragging the slider.
Click on OK button. Click on Apply button and OK button.
Cursor on canvas.

Use mouse wheel to zoom in.

Zoom in the map.

On the canvas now we see an enhanced topography of the landscape.


Slide Number 8

Summary

Let us summarize,

In this tutorial we have learnt to

  • Download DEM data from SRTM data website.
  • Show Hillshade of DEM.


Slide Number 9

Assignment 1

Here is the assignment.
  • Visualize the terrain using Slope mode for the raster map.
  • Change the symbology for the Slope layer
  • Hint: Select the Mode as Slope and use it as overlay.
Cursor on the interface. Your completed assignment should look as shown here.


Slide Number 10

About Spoken Tutorial Project

  • This video summarizes the Spoken Tutorial project
  • Please download and watch it.
Slide Number 11

Spoken Tutorial Workshops

  • We conduct workshops using Spoken Tutorials and give certificates.
  • Please contact us.


Slide Number 12

Forum for Specific questions

Please post your timed queries on this forum
Slide number 13

Acknowledgements

The Spoken Tutorial Project is funded by NMEICT, MHRD Government of India.
This tutorial is contributed by Vaishnavi Honap from college of Engineering Pune,

Snehalatha Kaliappan and Himanshi Karwanje from IIT Bombay.

Thank you for joining.

Contributors and Content Editors

Karwanjehimanshi95, Snehalathak

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