Practical Manual for RS and GIS with Quantum GIS

1. GEOREFERENCING OF TOPOSHEET

Aim: To georeference the given toposheet by using georeferencer. Introduction:

Georeferencing is the process of assigning real-world coordinates to each pixel of the raster. These coordinates are obtained by doing field surveys - collecting coordinates with a GPS device for few easily identifiable features in the image or map. In case of digitize scanned maps, the coordinates can be obtained from the markings on the map image itself. Using these sample coordinates or GCPs (Ground Control Points), the image is warped and made to fit within the chosen coordinate system.

Methodology:-

- Click on start button on the desktop.
- Select programs and go to Quantum GIS Lisboa.
- Then go to Quantum GIS Desktop 1.8.
- Click on raster on menu bar and go to georeferencer and again click on georeferencer.
- Change the transformation settings.
- Select appropriate transformation type.
- Select appropriate resampling method.
- Select target SRS to give coordinate reference system.
- Add toposheet by clicking on open raster button.
- Click on add points button and add ground control points in Degrees Minutes and Seconds mode at extreme corner points in pixel zoom mode by using pan, zoom in, zoom out buttons.
- The points can be edited in the GCP table which can be opened through view tab.
- Now click on start georeferencing button.
- Select the name and destination to save the file.
- Click on ok button and check the box load into canvas when finished.(Automatically the georeferenced toposheet is loaded into the canvas)
- Close the georeferencer window.
- The georeferenced toposheet will be stored in TIFF format.

- To view the georeferencered toposheet, now go to add raster button and click on to zoom to layer extent.
- Compare the co-ordinates with the toposheet.
- If the coordinates are correct then the toposheet is said to be georeferenced.

Result:

The toposheet is georeferenced as per the coordinates marked with required transformation and hence can be used for further analysis.

2. DIGITIZATION OF TOPOSHEETS USING POINT FEATURE

Aim: To digitize the given toposheet using point feature

Introduction:

- The process of representing an analogue signal or an image by a discrete set of its points

is known as Digitizing. This data after conversion is in the binary format, which is directly readable by computer. The analogue signals are variable whereas the digital format is the discrete one. These discrete units are called as bits. These bits organized in groups are known as byte. The digital signals are mainly represented in the form of sequence of integers. These integers can be converted back to analogue signal that are approximately similar to the original analogue signals. Digitizing is done by reading an analogue signal at regular time intervals, representing the value of that point by an integer. The process of digitization is classified into manual digitizing, heads up digitizing, interactive tracing method and automatic digitizing. Manual Digitizing is done using digitizing tablet. The operator manually traces all the lines from his hardcopy map and creates identical digital map on the computer. It is very time consuming and level of accuracy is also not very good. Heads-up Digitizing is similar to manual digitizing in the way that lines have to be drawn manually but directly on the computer screen. So in this level of accuracy increases and time taken decreases. Interactive tracing method is improvement over Heads-up digitizing in terms of speed and accuracy. Automatic Digitizing is automated raster to vector conversion using image processing and pattern recognition techniques In this technique computer traces all the lines, which results in high speed and accuracy along with improved quality of images.

Methodology:-

- Click on start button on the desktop.
- Select programs and go to Quantum GIS Lisboa.  Then go to Quantum GIS Desktop 1.8.  Click on add raster layer on tool bar
- Add georeferenced toposheet which is saved as .tif file.
- Right click on the layer in TOC and opt for zoom to layer extent.  Go to layer on menu bar and click on new.
- Select new shape file layer.
- Then select point type.
- Fill the details in the new vector layer window and select name of the file, type, width to be provided.
- Coordinate reference system should be selected and it should be same as the georeferenced toposheet.
- Click on ok.
- Select the destination for saving the file.
- Make right click on the project name and open the attribute table.
- Select toggle editing.
- Then click on add columns.
- Fill the details like name of the column, type, width to be provided.
- Click on ok and close the window.
- Go to toggle editing and click on add features.
- Select point features and provide ID and name.
- Save the file by clicking on save project.
- Click on file on menu bar and go to new print composer.
- Go to layout and click on add image to add an image, add label to add title, add legend to add a legend, add scale bar to add a scale bar and add North arrow via add image tool.
- Go to file and click on export as pdf for saving the file in pdf format or click on export as image to save the file as image.
- Provide the name for the output file and select the destination for saving the file.

Result:

The point features like spot heights and villages were digitized using the point features.

3. DIGITIZATION OF TOPOSHEETS USING LINE FEATURE Aim: To digitize the given toposheet using line feature

Introduction:

- The process of representing an analogue signal or an image by a discrete set of its points is known as Digitizing. This data after conversion is in the binary format, which is directly readable by computer. The analogue signals are variable whereas the digital format is the discrete one. These discrete units are called as bits. These bits organized in groups are known as byte. The digital signals are mainly represented in the form of sequence of integers. These integers can be converted back to analogue signal that are approximately similar to the original analogue signals. Digitizing is done by reading an analogue signal at regular time intervals, representing the value of that point by an integer. The process of digitization is classified into manual digitizing, heads up digitizing, interactive tracing method and automatic digitizing. Manual Digitizing is done using digitizing tablet. The operator manually traces all the lines from his hardcopy map and creates identical digital map on the computer. It is very time consuming and level of accuracy is also not very good. Heads-up Digitizing is similar to manual digitizing in the way that lines have to be drawn manually but directly on the computer screen. So in this level of accuracy increases and time taken decreases. Interactive tracing method is improvement over Heads-up digitizing in terms of speed and accuracy. Automatic Digitizing is automated raster to vector conversion using image processing and pattern recognition techniques In this technique computer traces all the lines, which results in high speed and accuracy along with improved quality of images.

Methodology:-

- Click on start button on the desktop.
- Select programs and go to Quantum GIS Lisboa.  Then go to Quantum GIS Desktop 1.8.  Click on add raster layer on tool bar
- Add georeferenced toposheet which is saved as .tif file.
- Right click on the layer in TOC and opt for zoom to layer extent.  Go to layer on menu bar and click on new.
- Select new shape file layer.
- Then select line type.
- Fill the details in the new vector layer window and select name of the file, type, width to be provided.
- Coordinate reference system should be selected and it should be same as the georeferenced toposheet.
- Click on ok.
- Select the destination for saving the file.
- Make right click on the project name and open the attribute table.
- Select toggle editing.
- Then click on add columns.
- Fill the details like name of the column, type, width to be provided.
- Click on ok and close the window.
- Go to toggle editing and click on add features.
- Select line features and provide ID and name.
- Save the file by clicking on save project.
- Click on file on menu bar and go to new print composer.
- Go to layout and click on add image to add an image, add label to add title, add legend to add a legend, add scale bar to add a scale bar and add North arrow via add image tool.
- Go to file and click on export as pdf for saving the file in pdf format or click on export as image to save the file as image.
- Provide the name for the output file and select the destination for saving the file.

Result:

The line features like roads, railways and contours were digitized using the line feature.

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