Georeferencing in ArcGIS
What is Georeferencing
Georeferencing means, a image convert to referenced or Earth coordinate system. The term is commonly used in the geographic information systems (GIS) field to describe the process of associating a physical map or raster image of a map with spatial locations.
Georeferencing refers to the process of assigning map coordinates to image data. The image data may already be projected onto the desired plane, but not yet referenced to the proper coordinate system. Image-to-image rectification involves georeferencing only if the reference image is already georeferenced.
In this Tutorial Learn Image to Image and Ground to Image Georeferencing in ArcGIS.
Perform Image to Image Georeferencing
1. First add to Basemap in ArcMap. Dropdown ‘+’ button and add a base map, and choose Topographic, or any others.
2. In the Catalog window expand the Folder (ex.- ArcGIS) that contains open unreferenced images, just drag it.
3. When you try to add any GIS data that missing spatial reference information in the ArcMap it will warn you. Click the OK button to close this warning message.
4. To display individual images in the map. select any one image from the Table of Content (TOC) window, click the right-button of the mouse and choose Zoom To Layer option.
5. If do not display the Georeferencing toolbar, click the Customize menu and click Toolbars> Georefencing, from the Georeferencing toolbar.
Click the Layer drop-down arrow and click the unreferenced raster layer that you want to georeference.
6. Minimum 4 points are required to complete this task. You can also collect maximum points to better accuracy for georeferencing.
Select Add point-click any particular place in unrectified image(Los angeles.jpg), then zoom to layer Basemap and zoom its same place and click it.
7. The same process follows to completed 4 points or many. You will show unrectified image automatically adjust the same area in the Basemap.
Just check it table to collect all points, open view link table, and show all the information.
Now finally rectify the unrectified image.
8. Dropdown arrow Georeferencing button, select Rectify. Now rectify window is open, select output lacation , you can change the name and file format, then click Save button.
Discard the unrectified image.
9. Already open a Basemap, now open Rectified image, you can swipe (available effects layer) and check it accuracy label of this georeferenced image.
Perform Ground to Image Georeferencing
1. From the right side Catalog window, drag the unrectified image (sikkim_disrict.jpg) to the map.
When you add this image, ArcMap generates a warning window, Because ArcMap does not found any spatial referencing information for this image.
You just click the Ok button and close this warning window.
2. Click the Add Control Points tool, click anyone cross point of this unreferenced image to add the source coordinate of the 1st link.
3. Click the right button of the mouse and select Input X and Y option from the pop-up window. Coordinates dialog box appears, enter the longitude(X) and latitude(Y) value.
4. Click OK, follow the same technique and add additional three links for the other three cross points (you can also generate more points to better accuracy).
5. Click the View Link Table(i) to evaluate the transformation. Input any wrong point or value choose select link(ii), select a point, and then press the delete button on your keyboard.
6. Select the Georeferencing dropdown menu and click Rectify. Save as window is appears, change the output location and also change name and file format, and click save.
7. Select the unreferenced image (sikkim_district) from the TOC(Table of Content) window and remove it. Now Save changes to the existing map window is open, click No button. Because now you don’t need to save this map.
8. Before adding the rectified image in the catalog window select rectified image (Sikkim_district_rectify), click the right button to choose Properties.
9. Scroll down the Raster Dataset Properties window, on the Spatial Reference Section, click Edit button.
In the Spatial Reference Properties window, expand the Geographic Coordinate Systems folder. Then expand the World subfolder and choose WGS 1984 coordinate system and click Ok button.
Change Projection (GCS to PCS)
Learn how to convert map in geographic coordinate system(GCS) to projected coordinate system(PCS).
1. Change the projection in a map, open Arc Toolbox(i). Arc toolbox window appears to expand Data manage tools, then expend projection and Transformation subgroup, expend Raster, select project raster, and double click it.
You also use the short cart method open search window(ii), search project raster in the box, the result is an automatic show.
2. Project raster pane is open, select input raster, choose a folder to output dataset, then click the output coordinate system button.
Expand the Projected Coordinate Systems folder and choose the required coordinate system, click OK and then press ok.
Open a new projected coordinate system image and check it.
