Georeferencing a raster dataset
When georeferencing, you should look for well-defined objects within your images, such as road intersections or land features. This way you can be certain that you are referencing the same location in both the raster dataset and aligned datasets.
In ArcMap, add the layers residing in map coordinates and then the raster dataset you want to georeference.
Adding the data with the map coordinate system first is a good workflow, so that you do not need to set the data frame coordinate system.
- To display the Georeferencing toolbar, click the Customize menu, point to Toolbars, then click Georeferencing.
- In the table of contents, right-click a target layer (the referenced dataset) and click Zoom to Layer.
- From the Georeferencing toolbar, click the Layer drop-down arrow and click the raster layer you want to georeference.
Click Georeferencing and click Fit To Display.
This displays the raster dataset in the same area as the target layers. You can also use the Shift and Rotate tools to move the raster dataset as needed. To see all the datasets, adjust their order in the table of contents.
- Click the Add Control Points tool to add control points.
To add a link, click a known location on the raster dataset and click a known location on the data in map coordinates (the referenced data).
You can also add your links in the Magnification window or the Viewer window. When working with two raster datasets, you can open the Image Analysis window and adjust the transparency or turn layers on and off in the table of contents to view each image as you add your links.Tip:Press ESC to remove a link while you're in the middle of creating it.Note:The Rotate and Shift tools are not available after you place the first link.
Add enough links for the type of transformation.
You need a minimum of 3 links for a spline or first-order polynomial, 6 links for a second-order polynomial, and 10 links for a third-order polynomial.
Click the View Link Table button to evaluate the transformation.
You can examine the residual error for each link and the RMS error. If you're satisfied with the registration, you can stop entering links.
- You can delete an unwanted link from the Link Table dialog box.
Click Georeferencing and click Update Georeferencing to save the transformation information with the raster dataset.
This creates a new file with the same name as the raster dataset but with an .aux.xml file extension. It also creates a world file for some of the file formats, including .tif and .img files.
You can permanently transform your raster dataset after georeferencing by using the Rectify command; click Georeferencing and click Rectify or use the Warp tool.