View source for QGIS/C4/DEM-Analysis/English-timed


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|| '''Time'''
|| '''Narration'''
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|| 00:01
||Welcome to this tutorial on '''DEM Analysis''' in '''QGIS'''.

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|| 00:07
|| In this tutorial, we will learn to,

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|| 00:11
|| Download '''DEM''' data from '''SRTM''' data website.

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|| 00:16
|| Show Hillshade of '''DEM'''.

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|| 00:19
|| Here I am using

'''Ubuntu Linux '''OS version 16.04

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|| 00:25
|| '''QGIS''' version 2.18 and 

A working internet connection.

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|| 00:33
|| To follow this tutorial you should be familiar with '''QGIS '''interface.

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|| 00:39
|| To view the prerequisite tutorials in this series, please visit this website.
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|| 00:45
|| '''Digital Elevation Model''' or '''DEM''' is a raster file.

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|| 00:50
|| It shows elevation data for each raster cell.

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|| 00:55
||'''DEMs''' are used to represent the bare earth terrain. 

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|| 01:00
|| The terrain is usually devoid of vegetation and man-made features.

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|| 01:06
|| '''DEMs''' are used for calculations and analysis of an area, based on the elevation.
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|| 01:14
|| Let us download '''DEM '''data.

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|| 01:17
|| Open the given link in any web browser.

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||01:21
|| '''Shuttle radar topography mission (SRTM) data''' website opens.

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|| 01:27
|| '''SRTM''' data from this website can be downloaded freely.

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|| 01:32
||On the '''Download Manager''' page, the elevation models are arranged into tiles.

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|| 01:39
|| Two options for '''Tile Size''' and '''Format''' are available.

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|| 01:44
|| We can choose the tile size and format by clicking the radio buttons.

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||01:50
||Scroll down the page to the world map.

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||01:54
||Use + sign on the left corner of the map to zoom in the world map.

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|| 02:00
||Click on '''Maharashtra''' tile.

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||02:03
||Click on '''Search''' button located on the top-left corner of the world map.

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||02:09
||'''Download''' window opens.

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|| 02:12
|| Scroll down to '''Description''' heading.

Click on '''Download SRTM''' link at the bottom.

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||02:20
||A dialog-box opens, select '''Save File''' option. Click on '''OK '''button.

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|| 02:29
|| On my system, '''zip file '''downloads to the '''Downloads '''folder.

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||02:34
|| Extract the contents of the '''zip file'''.

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|| 02:38
|| Right-click and select '''Extract Here '''option.

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|| 02:43
|| Double-click on the extracted folder.

This is a '''DEM''' '''dataset'''.

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|| 02:50
|| Here we see many files with different file extensions.

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||02:55
||Close the folder.

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||02:57
|| Open the '''QGIS '''interface.

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|| 03:00
|| Click on, '''Layer menu '''on the '''menu bar'''.

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|| 03:04
|| Select '''Add Layer, '''from the '''sub-menu''', click on '''Add Raster Layer '''option.

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|| 03:11
|| '''Data source '''dialog-box''' '''opens.

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|| 03:14
|| Navigate to the '''SRTM '''folder downloaded from the '''SRTM ''' website.

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|| 03:21
|| From the contents of the folder, select the file with '''.tif '''extension.

Click on '''Open '''button.

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||03:31
||On the canvas you will see '''DEM''' of the terrain.

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|| 03:36
|| '''DEM''' contains all the '''3D information''' about the terrain.

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|| 03:41
|| Each pixel on the raster image represents the average elevation at that location.

This elevation is given in meters.

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|| 03:52
|| Dark pixels represent areas with low altitude.

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|| 03:57
|| Lighter pixels represent areas with high altitude.

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||04:02
||Let us begin the '''DEM '''analysis of this map.

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|| 04:07
|| Click on '''Raster '''menu on the menu bar.

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|| 04:11
|| Click on '''Analysis''' from drop down.

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

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||04:19
|| '''DEM''' dialog-box opens.

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|| 04:22
|| Input file field has '''DEM layer '''as the default selection.

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||04:28
|| Click on '''Select '''button next to '''Output file'''. 

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||04:33
|| '''Save the results to..''' Dialog-box opens.

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|| 04:37
|| In the dialog-box, name the file as '''Hillshade.tif.'''

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|| 04:44
||I will save it on the '''Desktop'''.

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|| 04:47
||Click on '''Save '''button.

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||04:50
|| Select''' Hillshade''' as''' Mode '''option.

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|| 04:54
||Here by default '''Hillshade '''is already selected.

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||04:59
|| Check the check-box next to '''Load into canvas when finished'''.

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||Here by default it is already selected.

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|| 05:09
||Leave the default settings as such.

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|| 05:12
||Click on '''Ok '''button.

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|| 05:15
|| A pop-up box opens with message '''Processing Completed'''.

Click on '''OK''' button.

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||05:22
||Click '''OK''' button in the '''Qgis.bin''' dialog-box.

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||05:27
||Click on '''Close''' button on the '''DEM''' dialog-box.

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||05:32
|| A new layer, '''Hillshade''' is now added in the '''Layers panel'''.

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|| 05:37
||On the canvas you will see a raster map in '''Hillshade''' mode.

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||05:42
||This map is generated using light and shadow to create a 3D image.

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||05:48
|| To make the model more pronounced, we will use '''Hillshade''' as an overlay. 

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||05:54
|| Now we will change the '''symbology''' of the original '''DEM''' layer.

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|| 05:59
|| Right-click on the '''srtm layer '''in the '''Layers''' Panel.

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|| 06:04
||From the context menu select '''Properties '''option.

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||06:09
|| '''Layer Properties''' dialog-box opens.

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|| 06:13
||Select '''Style''' from the left panel.

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||06:17
|| Under '''Band Rendering '''section, change the '''Render type '''to '''Singleband pseudocolor.'''

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|| 06:24
|| Under '''Load minimum/maximum values''', click on '''minimum/maximum '''radio button.

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||06:33
|| Select''' Linear''' from '''Interpolation '''drop-down.

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|| 06:37
||This is a default selection here.

From the '''Color '''drop-down select '''Spectral'''.

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|| 06:44
|| Scroll down.

Select '''Mode '''as '''Continuous '''from the drop down.

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|| 06:50
||Click on '''Classify '''button.

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||06:53
|| '''5''' new color values are created.

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|| 06:57
||The colors represent values of elevation of raster from lowest to highest.

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||07:04
||Click on '''Apply''' button and '''OK''' button at the bottom right corner.

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|| 07:10
|| In the '''Layers''' panel, disable the '''Hillshade''' layer .

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|| 07:14
||Uncheck the check-box against '''Hillshade''' layer.

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||07:18
||Now on the canvas you will see a map in spectral colors.

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||07:24
|| The red shaded terrain is least elevated and blue is most elevated.

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|| 07:30
||Enable the '''Hillshade layer'''.

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||07:33
|| Open the '''Layers Properties''' dialog-box.

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|| 07:37
|| Select '''Transparency''' from left panel.

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|| 07:41
|| Set the '''Global transparency''' to 50% by dragging the slider.

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||07:47
|| Click on '''Apply '''button and '''OK '''button.

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|| 07:51
|| Zoom in the map.

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|| 07:53
||On the canvas now we see an enhanced topography of the landscape.

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|| 08:00
|| Let us summarize,

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|| 08:03
||In this tutorial we have learnt to

Download '''DEM''' data from '''SRTM''' data website.

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|| 08:11
||Show Hillshade of '''DEM'''.

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|| 08:15
|| Here is the assignment.

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|| 08:17
|| Visualize the terrain using '''Slope''' mode for the raster map. Change the symbology for the '''Slope''' layer

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|| 08:27
|| Hint: Select the '''Mode''' as '''Slope''' and use it as overlay. 

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||08:33
||Your completed assignment should look as shown here.

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|| 08:38
|| This video summarizes the Spoken Tutorial project. Please download and watch it.

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|| 08:45
||  We conduct workshops using Spoken Tutorials and give certificates. 

Please contact us.
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|| 08:54
||Please post your timed queries on this forum

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|| 08:58
|| The Spoken Tutorial Project is funded by '''NMEICT, MHRD''' '''Government of India'''. 

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||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. 
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