Geo-reference Archives -

Georeference a map with the help of another georeferenced map

Here we will see how to georeference a map with the help of another georeferenced map in QGIS (Quantum GIS). Georeference is a process to associate geographic location coordinates to any kind of physical object which is physically present over a Raster image map or to a physical map, with help of other georeferenced data or with know location coordinates of some points of image which is effectively called as control points. It is one of the important concept of GIS (Geographical Information System). We have already discussed about how to Georeference Map with the help of know control points.

New to QGIS – Check other tutorial in QGIS.

Georeference a map with the help of another georeferenced map:

1.) Open QGIS and Load the georeferenced map, by selecting Layer -> Add Layer -> Add Raster Layer or by directly selecting Add Raster Layer from Layer panel as shown below.

2.) After loading the file, from the menu select Raster and click on Georeferencer to select Georeferencer.

3.) In the Georeferencer window which is open up by above step, select Add Raster Layer icon to load non georeference map.

4.) Click add point and select a point on your map. In the pop up window click from map canvas.

Georeference a map with the help of another georeferenced map

5.) Select location in the georeferenced map same as the location you selected in non-georeferenced map. You will see it will load the coordinates.

6.) Click ok.

7.) Likewise select at least four points in different direction. Click transformation setting icon button as shown below in image.

8.) Select any one Transformation Type and provide your output raster name.

9.) Click start Georeferencing button from the Georeferencer window.

10.) Select CRS same as the georeferenced map. In our case it is WGS 84. Close georeferencer. You will see georeferenced image in canvas. Note the coordinates.

I hope this article would be helpful for you to know the basics of how to georeference raster image with the help of another georeferenced map. If you are facing problem in implementing the process do comment below, so that we can discuss over it.

How to Georeference Map Image with Geo Coordinate Control points

How to Geo-reference Map Image with Geo Coordinate points in QGIS (Quantum GIS). Georeference is a process to associate geographic location coordinates to any kind of physical object which is physically present over a Raster image map or to a physical map, with help of other georeferenced data or with know location coordinates of some points of image which is effectively called as control points. Georeference is one of the important concept of GIS (Geographic Information System). Here we will see how to Georeference map manually in QGIS. You can also see how to georeference from one map to another and other QGIS tutorial.

Here is the steps to georeference raster image map in QGIS:

1.) Open QGIS and Import your image map using ADD RASTER LAYER in QGIS.

2.) We need to find the control point and known geolocation coordinates. I prefer Google Maps to get the Latitude and Longitude values.

Go to google map and search the location which matches your image map location on it. Select a point in google map which matches in your map. You can also switch to satellite view. Select a point such as any land mark place as per your convenience. Right click on that point in Google Map and click what’s here you will see it will display latitude and longitude of the point.

Georeference Map Image with Geo Coordinate Control points in QGIS 1

3.) Latitude is written first and the second one is longitude. Also notice (-) sign (if present). Note down the points. Likewise select at least 4 points in different directions and note down the latitude and longitude of them.

4.) Moving to QGIS tool, Right click on the Raster layer and click remove.

5.) Now go to Georeferencer, you will find it in Raster tab, if you already have installed georeferencer plugin. If you don’t see the option, click Plugins and then select manage and install plugins. Search for georeferencer and install the same as shown below.

Georeference Map Image with Geo Coordinate Control points in QGIS

6.) Import your map here and click add points. You can pan and zoom here.

7.) Click on the location on your map which you selected on google map as control points. You will see a window demanding X,Y values. Put longitude value in X and latitude value in Y.

8.) Like wise add all the points. Go to Settings and click Transformation Setting.

9.) Select any one Transformation Type and Give your output raster name.

10.) Click load in to map canvas when done or if you forget to do so you can import the georeferenced map from the location where you saved it. The extension for the map will be .GeoTiff.

11.) Select CRS WGS: 84 because we are using Latitude and Longitude.

12.) Now click start Georeferencing symbol as shown below:

13.) Close georeferencer. You will see georeferenced image in canvas. Note the coordinates.

I hope this article would be helpful for you to know the basics of how to georeference raster image with the help of control points. You are getting problem in implementing the process do comment below, so that we can discuss over it.

Geo-Referencing raster image in QGIS w.r.t. vector file

Geo-Referencing raster image in QGIS with respect to vector file. Geo referencing is the process used to provide geographical information to the raster images like cadastral maps, physical maps and satellite imagery with the help of projection or coordinate system. As an ordinary raster image formed by the number of pixel which has no particular size, Geo-referencing gives a particular coordinate to a pixel with respect to the ground point, it represents. Thus every individual pixel get its coordinate and size.

Look for other QGIS tutorial.

There are many GIS tools which perform Geo-referencing like ArcGIS, PCI Geomatica, Erdas Imagine, QGIS etc. Here Geo-referencing is shown in QGIS:

Geo-Referencing raster image in QGIS with respect to vector file

In QGIS first start with loading the vector file in QGIS environment by click on add vector layer.

Once the vector layer is loaded it can be given symbology by right click on the layer in the layers window. For geo-referencing the click on the georefrencer tab present at bottom of the QGIS environment window as shown below.

This will open a new window named Georeferencer . In this window open the raster image to be referenced by click on the tab open raster layer present on the top left corner.

When raster is open in the georefrencer window to add control points according to which raster will be georefrenced click on the add point button on the tool bar. Control points are the coordinate points of the ground or the projected coordinates.

These control points may be enter manually or from the map canvas as here reference is vector layer which is present on the map canvas. click on from map canvas on Enter map coordinates window.

This will open the map canvas or main QGIS window , select the point of reference on the vector layer.

Selection of point on vector layer will fill in the XY coordinates on the Enter map coordinates window. In this way first control point is marked.

Following same procedure select more and more points with minimum residual error which is generated by the tool and shown in the GCP table window.

Residual error is the difference between the actual coordinate of the control points and the geographic coordinate created by control points. The residuals represent the level of accuracy of the georefrenced images.

Check more :

Georeference on Map image with Geo Coordinates Control

Change projection of a georeference

These georefrenced images can be placed in the layers of any Geographic information system and can be used to locate points on the ground. Feel free to comment below, if you are having any problem to Geo-Referencing raster image or if you want to discuss for the same topic.