QGIS/C4/Interpolation/English - Revision history

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Snehalathak at 06:38, 5 January 2021

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Snehalathak at 12:47, 28 January 2020

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Madhurig at 07:31, 28 January 2020

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Karwanjehimanshi95: Created page with " {|border=1 || '''Visual Cue''' || '''Narration''' |- || '''Slide Number 1''' '''Title Slide''' || Welcome to this tutorial on '''Interpolation Methods''' in QGIS. |- || ''..."

2020-01-20T10:01:21Z

Created page with " {|border=1 || '''Visual Cue''' || '''Narration''' |- || '''Slide Number 1''' '''Title Slide''' || Welcome to this tutorial on '''Interpolation Methods''' in QGIS. |- || ''..."

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{|border=1
|| '''Visual Cue'''
|| '''Narration'''
|-

|| '''Slide Number 1'''

'''Title Slide'''
|| Welcome to this tutorial on '''Interpolation Methods''' in QGIS.

|-
|| '''Slide Number 2'''

'''Learning Objectives'''
|| In this tutorial, we will learn about Interpolation methods.

* '''Inverse Distance Weighting (IDW)''' and

* '''Triangulated Irregular Network (TIN)'''

|-
|| '''Slide Number 3'''

'''System Requirement'''
|| Here I am using

'''Ubuntu Linux''' OS version 16.04

'''QGIS''' version 2.18

|-
|| '''Slide Number 4'''

'''Pre-requisites'''
|| To follow this tutorial you should be familiar with QGIS interface.

For the prerequisite tutorials in this series, please visit this website.

|-
|| '''Slide Number 5'''

'''Example for Demonstration'''

|| Data files required for this tutorial are provided in the Code files link.

Please download and extract the contents of the folder.

|-
|| Cursor on the code files folder.

Double click on the code file folder.
|| I have saved this folder on the Desktop.

Double-click on the folder to open it.

|-
|| Cursor on '''Airstations.shp'''
|| Locate '''AirStations.shp''' in the extracted folder.

This file shows meteorological stations located in Maharashtra.

|-
|| '''Slide Number 6'''

'''About Interpolation'''

Interpolation is a method to create continuous surface from discrete points.

Two methods of interpolation are available in QGIS.

* '''Inverse Distance Weighting (IDW)'''
* '''Triangulated Irregular Network (TIN)'''

|| Interpolation is a method to create continuous surface from discrete points.

Two methods of interpolation are available in QGIS.

* '''Inverse Distance Weighting (IDW)'''
* '''Triangulated Irregular Network (TIN)'''

|-
|| '''Slide Number 7'''

'''About Interpolation'''
|| '''Interpolation Plugin''' is used to create '''interpolated raster''' from '''Point layer'''.

|-
|| Open the QGIS interface.

Click on '''Plugins''' menu, Select '''Manage and install Plugins'''.

In the '''Plugins''' dialog-box search for '''Interpolation plugin'''.

Check the check-box for '''Interpolation plugin'''.
|| Open the QGIS interface.

Here I have opened the QGIS interface.

Enable the interpolation plugin using '''Plugins''' menu as shown here.

Check the check-box for '''Interpolation plugin'''.

Close the dialog-box.

|-
|| Click on '''Raster''' menu.

Cursor on the interpolation option.
|| Open the '''Raster''' menu.

'''Interpolation''' option is now added in the '''Raster''' menu.

|-
|| Click on''' Add Vector Layer '''tool from the left panel.

Point to the dialog-box.
|| Click on '''Add Vector Layer''' tool.

'''Add vector layer''' dialog-box opens.

|-
|| Click on the '''Browse''' button>>'''Desktop'''>>'''Interpolation-code-files'''.
|| Click on '''Browse''' button and

Navigate to code files folder.

Here we will select two files.

|-
|| Click on '''AirStations.shp''' file.
|| Select '''AirStations.shp''' file.

|-
|| Hold the Ctrl key on the keyboard and click on '''MH_Districts .shp'''.
|| Hold the Ctrl key on the keyboard and click on '''MH_Districts.shp'''.

|-
|| Click on '''Open''' button in the '''Open an OGR Supported Vector Layer''' dialog-box.

Click on '''Open''' button on the '''Add vector layer''' dialog-box.
|| Click on the '''Open''' button.

Click on '''Open''' button on the '''Add vector layer''' dialog-box.

|-
|| Cursor on the canvas.

Using cursor show the point features.
|| On the canvas we see map of Maharashtra state.

Locations of Air stations in each district are shown as point features.

|-
|| '''Add labels''' for Air Stations.

Right click on the '''Air Stations layer>> Properties'''.

'''Layer Properties''' dialog-box opens.
|| Let us label these '''point features'''.

Right click on the '''Air Stations layer'''.

Click on '''Properties '''option to open''' Layer Properties''' dialog box.

|-
|| Select the '''labels''' option located at the left side.
|| Select the '''Labels''' option located on the left panel.

|-
|| Click on the drop-down located at the top.

Select the '''Single Labels for this layer''' option from dropdown.
|| Click on the drop-down located at the top.

Select '''Show labels for this layer''' from the drop-down.

|-
|| From new menu click on the '''Label With''' Option.

Select '''Air_Pollut''' from the drop-down.
|| In the '''Label With''' drop-down select '''Air_Pollut'''.

Scroll down.

|-
|| Point to the options.
Click on '''OK''' button.
|| Here you will find various options to modify the label style.

Choose the required style and click on '''OK''' button.

|-
|| Cursor on the canvas.
|| On the canvas, points with the labels will be displayed.

|-
|| Point towards the '''Air Stations''' layer on Layers panel.
|| Open the attribute table for '''Air Stations.shp''' layer.

|-
|| Cursor on the first column of the '''Attribute table'''.

Cursor on the '''Nox''' Column.
|| In the attribute table there are five columns.

In the 4th column, Nitrogen Oxides levels for every station is given.

|-
|| Cursor on the interface.

Click on''' Close''' button.
|| We will interpolate '''Air Stations''' layer by the '''Nox''' attribute.

Here we will use '''IDW method''' for interpolation.

Close the attribute table.

|-
|| '''Slide number 8'''

'''IDW Interpolation'''

|| '''Inverse Distance Weighting''' method gives weights to sample points.

It is used for interpolating data such as temperature, rainfall, population etc.

|-
|| Open QGIS interface.
|| Back to the QGIS interface.

|-
|| Click on the '''Raster''' menu.

Locate the '''Interpolation''' Plugin.
|| Click on the '''Raster''' menu.

|-
|| Click on the '''Interpolation''' plugin.

Cursor on the dialog-box.
|| Click on the '''interpolation '''plugin.

'''Interpolation plugin''' dialog-box opens.
|-
|| Cursor on the '''Input'''.

Select '''Air Stations '''from''' Vector layers'''.

Cursor on the '''Air Stations'''.

|| In the''' Input''' section,

Select '''Air Stations''' as option as the '''Vector layers'''.

Here, by default, '''Air Stations''' layer is already selected.

|-
|| Select '''Interpolation''' attribute as '''NOx'''.
|| Select '''Interpolation''' attribute as '''NOx'''.

|-
|| Click on the '''Add '''Button.

'''Air Stations.shp''' layer with '''NOx''' attribute is seen in the panel.

Click on '''Types '''drop-down and select '''Points.'''

|| Click on the '''Add '''Button.

This will add '''Air Stations.shp''' layer with '''NOx''' attribute.

Select '''Points '''in the''' Type '''drop-down.

Here '''Points''' is selected by default.

|-
|| Select '''Inverse Distance Weighting (IDW) '''from '''Interpolation Method'''

drop-down.
|| Go to the '''Output''' section.

Select '''Interpolation method''' as '''Inverse Distance Weighting'''.

Leave all the Settings as '''default'''.

|-
|| Click on the three dots button next to''' Output File'''.

Give the name as '''IDW _Stations'''.

Save it on the '''Desktop''' and click on '''Save''' button.
|| Click on the three dots button''' '''next to '''Output file'''.

Save the output as an '''IDW_Stations''' in the desire folder.

I will save it on '''Desktop'''.

|-
|| Check the check-box '''Add result to project'''.
|| Check, '''Add result to project''' if it is unchecked.

|-
|| Click on '''OK''' button.
|| Click '''OK''' button.

|-
|| Cursor on the map.

Point to White areas.

|| The map with '''black''' and '''white''' areas will be displayed on the screen.

White areas represent high levels of '''Nitrogen Oxides'''.

|-
|| Point to black areas.
|| Black areas represent low levels of '''Nitrogen Oxides'''.

|-
|| Point Towards '''Interpolation_Stations''' layer.

Right click on '''IDW_Stations''' layer>>Select '''Properties'''.
|| For more clarity, we will change the symbology of layer.

Open '''Layer properties''' for the '''IDW''' layer.

|-
|| From the left panel, click on the '''Style''' option.

Select '''Render type''' as '''Single band Pseudocolor'''.
|| From the left panel, click on the '''Style '''option.

Select '''render type''' as '''Single band Pseudocolor'''.

|-
|| Click on '''Interpolation '''drop down and select '''Discrete'''.

Select '''Spectral''' from '''Color''' drop-down.

Check the check-box as '''Invert'''.
|| Select '''Discrete''' from '''Interpolation''' drop-down.

Choose '''Spectral''' from color drop-down.

Check the '''Invert''' check-box.

|-
|| Cursor on '''classify''' tab.

Click on '''Apply''' and '''OK'''.
|| Click on the '''classify''' button.

Leave all other settings as '''default'''.

Click on '''Apply''' and '''OK''' button.

|-
|| Cursor on '''the QGIS interface'''.

Point to red area.

Cursor on blue area.

|| Map with areas in '''Spectral''' colors is displayed on the canvas.

The red colored areas have high concentration of '''Nitrogen Oxides'''.

Blue areas have least concentration of '''Nitrogen Oxides'''.

|-
|| '''Save''' Your Results.

Give the name as''' IDW-Station'''.

Save it on the''' Desktop'''.

Click on '''Save '''button.

|| Save the project using '''Save''' tool from the tool bar.

Give an appropriate name.

Choose a convenient location.

Click on '''Save''' button.

|-
|| '''Slide number 9'''

'''TIN Interpolation Method'''
|| Let us now learn about the '''Triangulated Irregular Network interpolation''' method.

'''TIN '''is used to create a surface formed by triangles.

This is based on '''nearest neighbor point '''information.

'''TIN '''method is commonly used for elevation data.

|-
|| Click on '''New''' tool on the tool bar.
|| Open a new '''QGIS''' window.

Click on '''New''' tool on the tool bar.

|-
|| '''Add Vector Layer>> Browser>> Navigate to Points.shp layer.'''

Right Click on '''Points.shp''' layer. Select '''Open Attribute Table'''.
|| Use the '''Add Vector Layer''' tool to load '''Points.shp''' layer.

Open '''Attribute table''' of '''Points''' layer.

|-
|| Point to '''Elevation '''data.
|| Notice the '''Elevation''' data for each '''Point feature.'''

|-
|| Close the '''Attribute''' table'''.
|| Close the '''Attribute''' table'''.

|-
|| Click on the '''Raster''' tab from the sub-menu select '''Interpolation'''.
|| Again open '''Interpolation window''' from '''Raster''' menu.

|-
|| In the '''Interpolation '''dialog-box select '''Points''' as '''Vector layers'''.

Select '''Elevation '''as''' Interpolation attribute'''.
|| In the''' Input''' section, select '''Points''' layer in the '''Vector layers''' drop-down.

Select '''elevation '''as''' Interpolation attribute'''.

|-
|| Click on''' Add''' button.

Cursor on the '''Points layer'''.
|| Click on '''Add '''Button.

This will add '''Points layer''' with '''Elevation attribute''' for '''interpolating'''.

'''Points''' in '''Type''' drop-down is chosen automatically.

Leave it as such.

|-
|| Select '''Triangular interpolation '''from the drop-down.

Click on the three dots button next to''' Output File'''.

Give the name as '''TIN-Stations.'''

Save it on the '''Desktop '''and click on '''Save '''button.

Click on '''OK '''button on the '''Interpolation plugin.'''
|| In the '''Output''' section, select '''Triangular interpolation''' as '''Interpolation method'''.

Save the '''output''' file as '''TIN-Stations''' and click '''OK.'''

|-
|| Cursor on the '''QGIS''' interface.
|| Map showing '''triangulated interpolation''' appears on the canvas.

|-
|| Right click on '''TIN-Stations '''layer>>Select '''Properties.'''

From the left panel, click on the '''Style '''option.

'''Select render '''type as '''Single band Pseudocolor. '''

Click on '''Interpolation '''drop down and select '''Discrete.'''

Select '''Spectral''' from '''Color''' drop-down.

Check the check-box as '''Invert.'''

Cursor on '''classify''' tab.

Click on''' Apply '''and''' OK.'''
|| Change the '''symbology''' for this layer.

Follow the same steps as we did for '''IDW''' layer.

|-
|| Cursor on the map.

Point to red area.

Point to blue area.
|| The map is now displayed in '''Spectral''' colors.

Areas in red represent high elevation.

Areas in blue represent low elevation.

|-
|| Save your Result
|| Save the maps using the '''Save''' tool on the toolbar.

|-
|| '''Slide Number 10'''

'''Summary'''
|| Let us summarize,

In this tutorial we have learnt about two methods of Interpolation.

* '''Inverse Distance Weighting (IDW)'''

* '''Triangulated Irregular Network''' '''(TIN)'''

|-
|| '''Slide Number 11'''

'''Assignment'''
|| For the assignment,

Create IDW Interpolated map for Air Stations layer with SO<sub>2 </sub>attribute.

|-
|| Show the glimpse of the map.
|| Your map should look as shown here.

|-
|| '''Slide Number 12'''

'''About the Spoken Tutorial Project'''

|| This video summarizes the Spoken Tutorial project.

Please download and watch it.

|-
|| '''Slide Number 13'''

'''Spoken Tutorial Workshops'''

|| The spoken tutorial project team conducts workshops and gives certificates.

For more details please write to us.

|-
|| '''Slide Number 14'''

'''Forum for specific question'''

|| Please post your timed queries in this forum.

|-
|| '''Slide Number 15'''

'''Acknowledgements'''
|| The Spoken Tutorial Project is funded by '''MHRD''' '''Government of India'''.

This tutorial is contributed by Ambadas Maske from College of Engineering Pune.

Snehalatha Kaliappan and Himanshi Karwanje from IIT Bombay.

Thank you for joining.
|-
|}

@@ Line 267: / Line 267: @@
 This will add '''Air Stations.shp layer''' with '''NOx''' attribute.
-Select '''Points '''in the ''' Type'''drop-down.
+Select '''Points '''in the ''' Type''' drop-down.
 Here '''Points''' is selected by default.

@@ Line 201: / Line 201: @@
 Cursor on the '''Nox''' Column.
-|| In the '''attribute''' table there are five columns.
+|| In the '''attribute''' table '''Nitrogen Oxides''' levels for every station is given.
-−
-In the 4th column, '''Nitrogen Oxides''' levels for every station is given.
 |-

@@ Line 75: / Line 75: @@
 || '''Interpolation''' is a method to create continuous surface from discrete points.
-Two methods of '''interpolation''' are available in QGIS.
+Two methods of '''interpolation''' are available in '''QGIS'''.
 * '''Inverse Distance Weighting (IDW)'''
@@ Line 195: / Line 195: @@
 |-
 || Point towards the '''Air Stations''' layer on Layers panel.
-|| Open the '''attribute''' table for '''Air Stations.shp''' layer.
+|| Open the '''attribute''' table for '''Air Stations.shp layer.'''
 |-
@@ Line 261: / Line 261: @@
 || Click on the '''Add '''Button.
-'''Air Stations.shp''' layer with '''NOx''' attribute is seen in the panel.
+'''Air Stations.shp layer''' with '''NOx''' attribute is seen in the panel.
 Click on '''Types '''drop-down and select '''Points.'''
@@ Line 320: / Line 320: @@
 Right click on '''IDW_Stations''' layer>>Select '''Properties'''.
-|| For more clarity, we will change the symbology of layer.
+|| For more clarity, we will change the symbology of the '''layer'''.
-Open '''Layer properties''' for the '''IDW''' layer.
+Open '''Layer properties''' for the '''IDW layer'''.
 |-
@@ Line 405: / Line 405: @@
 || '''Add Vector Layer>> Browser>> Navigate to Points.shp layer.'''
-Right click on '''Points.shp''' layer. Select '''Open Attribute Table'''.
+Right click on '''Points.shp layer'''. Select '''Open Attribute Table'''.
 || Use the '''Add Vector Layer''' tool to load '''Points.shp layer.'''
-Open '''Attribute table''' of '''Points''' layer.
+Open '''Attribute table''' of '''Points layer'''.
 |-
@@ Line 426: / Line 426: @@
 Select '''Elevation '''as''' Interpolation attribute'''.
-|| In the''' Input''' section, select '''Points''' layer in the '''Vector layers''' drop-down.
+|| In the''' Input''' section, select '''Points layer''' in the '''Vector layers''' drop-down.
 Select '''elevation '''as''' Interpolation attribute'''.
@@ Line 461: / Line 461: @@
 |-
-|| Right click on '''TIN-Stations '''layer>>Select '''Properties.'''
+|| Right click on '''TIN-Stations layer'''>>Select '''Properties.'''
 From the left panel, click on the '''Style '''option.

@@ Line 454: / Line 454: @@
 || In the '''Output''' section, select '''Triangular interpolation''' as '''Interpolation method'''.
-Save the '''output''' file as '''TIN-Stations''' and click '''OK.'''
+Save the '''output''' file as '''TIN-Stations''' and click '''OK button.'''
 |-

@@ Line 56: / Line 56: @@
 |-
-|| Cursor on '''Airstations.shp'''
+|| Cursor on '''Air Stations.shp'''
-|| Locate '''AirStations.shp''' in the extracted folder.
+|| Locate '''Air Stations.shp''' in the extracted folder.
 This file shows meteorological stations located in Maharashtra.
@@ Line 77: / Line 77: @@
 Two methods of '''interpolation''' are available in '''QGIS'''.
-* '''Inverse Distance Weighting (IDW)'''
+* '''Inverse Distance Weighting (IDW)''' and
 * '''Triangulated Irregular Network (TIN)'''
@@ Line 148: / Line 148: @@
 || On the canvas we see map of Maharashtra state.
-Locations of Air stations in each district are shown as point features.
+Locations of '''Air stations''' in each district are shown as point features.
 |-
 || '''Add labels''' for Air Stations.
-Right click on the '''Air Stations layer>> Properties'''.
+Right click on the '''Air Stations layer >> Properties'''.
 '''Layer Properties''' dialog-box opens.
@@ Line 160: / Line 160: @@
 Right click on the '''Air Stations layer'''.
-Click on '''Properties '''option to open''' Layer Properties''' dialog box.
+Click on '''Properties '''option to open '''Layer Properties''' dialog box.
 |-
@@ Line 269: / Line 269: @@
 This will add '''Air Stations.shp layer''' with '''NOx''' attribute.
-Select '''Points '''in the''' Type '''drop-down.
+Select '''Points '''in the ''' Type'''drop-down.
 Here '''Points''' is selected by default.
@@ Line 434: / Line 434: @@
 Cursor on the '''Points layer'''.
-|| Click on '''Add '''button.
+|| Click on '''Add''' button.
 This will add '''Points layer''' with '''elevation attribute''' for '''interpolating'''.
@@ Line 504: / Line 504: @@
 In this tutorial we have learnt about two methods of '''Interpolation'''.
-* '''Inverse Distance Weighting (IDW)'''
+* '''Inverse Distance Weighting (IDW)''' and
 * '''Triangulated Irregular Network''' '''(TIN)'''