Difference between revisions of "Digitizing in QGIS"

From CUOSGwiki
Jump to navigationJump to search
Line 6: Line 6:
   
 
==Software==
  
==Software==
−
The software that will be used for this tutorial is QGIS 2.18.15. QGIS is a user friendly open source geographic information system, it runs on Linux, Unix, Mac OSX, Windows and Android and supports numerous vector, raster and database formats and functionalities. The software can be downloaded at [[https://qgis.org/en/site/forusers/download.html| QGIS]]
 +
The software that will be used for this tutorial is QGIS 2.18.15. QGIS is a user friendly open source geographic information system, it runs on Linux, Unix, Mac OSX, Windows and Android and supports numerous vector, raster and database formats and functionalities. The software can be downloaded at [[https://qgis.org/en/site/forusers/download.html| QGIS]].
   
 
==Data==
  
==Data==
Line 17: Line 17:
 
Make sure to have QGIS downloaded and an aerial image saved to a location that it can be accessed.
  
Make sure to have QGIS downloaded and an aerial image saved to a location that it can be accessed.
 
===Starting New Project===
 
===Starting New Project===
−
For this tutorial we will want to create a new project where all of the data will be stored
 +
For this tutorial we will want to create a new project where all of the data will be stored.
 
*Along the main toolbar locate the "Project" tab-->New
  
*Along the main toolbar locate the "Project" tab-->New
   
Line 24: Line 24:
 
*The "Add raster layer" button is located along the left panel
 
*The "Add raster layer" button is located along the left panel
 
[[File:addrasterlayer1.png]]
  
[[File:addrasterlayer1.png]]
−
*locate the drive that you saved your aerial photo in and click "Open"
 +
*Locate the drive that you saved your aerial photo in and click "Open"
 
*Your aerial photo should now be open on the QGIS canvas, you can use the "Zoom in" tool[[File:zoominpic.png]] and the "Zoom out" tool[[File:zoomout.png]]to help you identify geographical features or land uses within the aerial image.
 
*Your aerial photo should now be open on the QGIS canvas, you can use the "Zoom in" tool[[File:zoominpic.png]] and the "Zoom out" tool[[File:zoomout.png]]to help you identify geographical features or land uses within the aerial image.
   
 
===Snapping Options===
  
===Snapping Options===
 
When digitizing there should be no gaps between vector layers, so setting up the snapping options will ensure that all lines and polygons are placed tightly together.
 
When digitizing there should be no gaps between vector layers, so setting up the snapping options will ensure that all lines and polygons are placed tightly together.
−
*along the main toolbar locate "Setting" and select "Options"
 +
*Along the main toolbar locate "Setting" and select "Options"
−
*the "Options" window will open and you will need to locate the "Digitizing" tab and click it
 +
*The "Options" window will open and you will need to locate the "Digitizing" tab and click it
−
* within the "Digitizing" tab you will see subheadings-locate "Snapping"
 +
*Within the "Digitizing" tab you will see subheadings-locate "Snapping"
 
*Within the "Snapping" subheading, you will set change the settings to the following:
  
*Within the "Snapping" subheading, you will set change the settings to the following:
 
**"Default snap mode" select "to vertex and segment"
  
**"Default snap mode" select "to vertex and segment"
Line 39: Line 39:
 
===Setting the Projection===
  
===Setting the Projection===
 
Before beginning to digitize the image, you need to make sure the correct projection is set for the image.
  
Before beginning to digitize the image, you need to make sure the correct projection is set for the image.
−
*to set the projection locate your aerial photo on the "Layer Panel"
 +
*To set the projection locate your aerial photo on the "Layer Panel"
 
[[File:imagelayertab.png]]
  
[[File:imagelayertab.png]]
−
*right click on the aerial photo and select "Properties"
 +
*Right click on the aerial photo and select "Properties"
−
** within the "General" tab in the properties window, locate the "Coordinate reference system" subheading and click on the "Coordinate tab" [[File:coordinatetab.png]]
 +
** Within the "General" tab in the properties window, locate the "Coordinate reference system" subheading and click on the "Coordinate tab" [[File:coordinatetab.png]]
−
**a window titled "Coordinate reference system selector" will open and within the filter search bar you can search for the appropriate coordinate system for the image you are using. For an aerial image of Ottawa the coordinate system will be MTM zone 9. Once you have selected your coordinate system click "Ok" and "Apply"
 +
**A window titled "Coordinate reference system selector" will open and within the filter search bar you can search for the appropriate coordinate system for the image you are using. For an aerial image of Ottawa the coordinate system will be MTM zone 9. Once you have selected your coordinate system click "Ok" and "Apply".
   
 
===Digitizing===
  
===Digitizing===
Line 49: Line 49:
 
* A new box will open, the first choice is whether you want to draw a point, line or polygon
  
* A new box will open, the first choice is whether you want to draw a point, line or polygon
 
**choose "line" as we will draw the roads within the image
  
**choose "line" as we will draw the roads within the image
−
*the next step is to set the projection so that the lines are within the same coordinate system as the aerial image
 +
*The next step is to set the projection so that the lines are within the same coordinate system as the aerial image
−
**click the "coordinate tab" [[File:coordinatetab.png]] and a new bow will open titled "Coordinate Reference System Selector". Within the filter option search for MTM zone 9 and select it and click "Ok"
 +
**Click the "coordinate tab" [[File:coordinatetab.png]] and a new bow will open titled "Coordinate Reference System Selector". Within the filter option search for MTM zone 9 and select it and click "Ok"
 
*Still within the "New shapefile layer" box, you will need to fill in the fields for the vector line. Under the subheading "New field" fill in the following;
 
*Still within the "New shapefile layer" box, you will need to fill in the fields for the vector line. Under the subheading "New field" fill in the following;
 
** Name; Roads
  
** Name; Roads
Line 57: Line 57:
 
**click "Add to fields list"
  
**click "Add to fields list"
 
**Within the "Fields list" box there is a default vector layer, you may want to delete this. You can delete it by selecting it and clicking the "Remove field" button
  
**Within the "Fields list" box there is a default vector layer, you may want to delete this. You can delete it by selecting it and clicking the "Remove field" button
  +
[[File:shapefilelayer1.png]]
  +
**Save your new shapefile, to the location that your project is saved
  +
*Along the main toolbar locate the "Toggle editing button"
  +
*select the
   
 
==Conclusion==
  
==Conclusion==

Revision as of 19:51, 19 December 2017

Purpose

The purpose of this tutorial is to demonstrate the process of creating a vector model by digitizing an aerial image within QGIS.

Objective

The objective is to retrieve an aerial image of the City of Ottawa and using QGIS software digitize the different land use classes and geographical features within the photo.

Software

The software that will be used for this tutorial is QGIS 2.18.15. QGIS is a user friendly open source geographic information system, it runs on Linux, Unix, Mac OSX, Windows and Android and supports numerous vector, raster and database formats and functionalities. The software can be downloaded at [QGIS].

Data

The data for this tutorial is a aerial photo that was retrieved from [Carleton Library Aerial Images]. The specific aerial image that was used in this tutorial was from the 2014 Orthophotos-National Capital Commission (20cm) and the region that was chosen was over Carleton University.

Methods

This section outlines the steps that will be taken to digitize the image.

Before Beginning

Make sure to have QGIS downloaded and an aerial image saved to a location that it can be accessed.

Starting New Project

For this tutorial we will want to create a new project where all of the data will be stored.

  • Along the main toolbar locate the "Project" tab-->New

Adding Aerial Image

To add the aerial image that was chosen and saved,it can be added into the QGIS canvas by using the "Add raster layer" button.

  • The "Add raster layer" button is located along the left panel
           Addrasterlayer1.png
  • Locate the drive that you saved your aerial photo in and click "Open"
  • Your aerial photo should now be open on the QGIS canvas, you can use the "Zoom in" toolZoominpic.png and the "Zoom out" toolZoomout.pngto help you identify geographical features or land uses within the aerial image.

Snapping Options

When digitizing there should be no gaps between vector layers, so setting up the snapping options will ensure that all lines and polygons are placed tightly together.

  • Along the main toolbar locate "Setting" and select "Options"
  • The "Options" window will open and you will need to locate the "Digitizing" tab and click it
  • Within the "Digitizing" tab you will see subheadings-locate "Snapping"
  • Within the "Snapping" subheading, you will set change the settings to the following:
    • "Default snap mode" select "to vertex and segment"
    • "Default snapping tolerance" set to "10.0 pixels"
    • Search radius" to "10.0 pixels"

Setting the Projection

Before beginning to digitize the image, you need to make sure the correct projection is set for the image.

  • To set the projection locate your aerial photo on the "Layer Panel"
       Imagelayertab.png
  • Right click on the aerial photo and select "Properties"
    • Within the "General" tab in the properties window, locate the "Coordinate reference system" subheading and click on the "Coordinate tab" Coordinatetab.png
    • A window titled "Coordinate reference system selector" will open and within the filter search bar you can search for the appropriate coordinate system for the image you are using. For an aerial image of Ottawa the coordinate system will be MTM zone 9. Once you have selected your coordinate system click "Ok" and "Apply".

Digitizing

  • Along the main toolbar locate "Layer" select "Create Layer" and select "New Shapefile Layer"
  • A new box will open, the first choice is whether you want to draw a point, line or polygon
    • choose "line" as we will draw the roads within the image
  • The next step is to set the projection so that the lines are within the same coordinate system as the aerial image
    • Click the "coordinate tab" Coordinatetab.png and a new bow will open titled "Coordinate Reference System Selector". Within the filter option search for MTM zone 9 and select it and click "Ok"
  • Still within the "New shapefile layer" box, you will need to fill in the fields for the vector line. Under the subheading "New field" fill in the following;
    • Name; Roads
    • Type; Text data
    • Length; leave the default value
    • click "Add to fields list"
    • Within the "Fields list" box there is a default vector layer, you may want to delete this. You can delete it by selecting it and clicking the "Remove field" button
               Shapefilelayer1.png
    • Save your new shapefile, to the location that your project is saved
  • Along the main toolbar locate the "Toggle editing button"
  • select the

Conclusion

Retrieved from "https://dges.carleton.ca/CUOSGwiki/index.php?title=Digitizing_in_QGIS&oldid=9474"