The source of an image, even if it is a screenshot, is not as critical as identifying the same objects in both the image and the real world and assigning accurate coordinates to these objects or control points. Control points are essential for georeferencing, as they establish the relationship between the “XY” coordinates of a raster image and real-world coordinates. In other words, they serve as the connection that enables the georeferencing of the image and determine its spatial location.
After loading the image and setting the coordinate system, the process of inserting control points can begin. If the image is not currently visible on the screen, the “Fit To Display” option in the “Prepare” group within the “Georeference” tab can be selected to make the image visible.
“Fit to Display” within the “Georeference” tab.
To georeference the image based on specific control points, the process starts by clicking on the “Add Control Points” icon found in the “Adjust” group of the “Georeference” tab. The cursor will change into a cross with the label “From point (source)” below it, allowing the user to select a known point in the image. After selecting the point, the label will switch to “To point (target)”.
To enter the real-world coordinates of the selected point, a right-click on the location will open a window titled “Target Coordinates”. In this example, values such as X: 691263 and Y: 9532775 are entered and confirmed by clicking “OK”.
It is possible that the image may no longer be visible after inserting the first control point. To address this, the user can right-click on the image in the “Contents” panel and choose “Zoom To Layer”.
This procedure should be repeated to add additional control points, such as a second point with coordinates X: 692075 and Y: 9532387. Generally, the use of more control points leads to higher accuracy in georeferencing. Geographic coordinates can also be entered in degrees, minutes, and seconds. To enable this format, the checkbox “Show Coordinates in DMS” should be activated.
Adding control points with the “Add Control Points” tool.
Once all control points have been correctly inserted, it is necessary to save the changes. This is done in the “Georeference” tab, within the “Save” group, by clicking the “Save” button. This step generates auxiliary files associated with the current image, storing the transformation data.
If it is preferred to keep the original image unchanged, the “Save as New” option should be selected. This creates a new version of the image with the georeferencing applied. To exit the georeferencing environment, the “Close Georeference” option located on the right side of the tab should be used.
To navigate directly to a specific location on the map, the “Go to XY” button, located in “Map > Navigate”, can be used. This tool accepts coordinates in multiple formats, enabling users to quickly reach the desired location.
Save georeferenced image.
The units used to display coordinates in the current map view can be customized. This adjustment is made from the bottom bar of the ArcGIS Pro interface, allowing users to choose the format most suitable for their work.
Change the map’s coordinate units.
