Georeference an Image

Use the Georeference Image command to geodetically position raster images in the Plan View by correlating specific pixels with known coordinates. This enables you to use imported, ungeoreferenced images, such as aerial photographs and scanned job site designs, as positionally accurate backgrounds for your data. You can also use this command to edit the position of an image that is already georeferenced.

By correlating two or more pixels with coordinates, you can change the planimetric orientation and scale of an image when you compute the transformation. The computations use the least squares method; the error is spread across all pixel / coordinate pairs so that the error is minimized (rubber-sheeting is not used). Once you have georeferenced an image, the pixel / coordinate pairs used for the computations are saved so you can modify the georeference at any time.

Prerequisites:

License; See the Subscription Plans page. For a license matrix by command, see the License page in the TBC Community. Also see View and manage licensed features.
Imported, ungeoreferenced image (.gif, .jpg, .png, or .tif)
Two or more known coordinates for features that can be correlated with specific pixels in the image

To access the command:

Select Georeference Image in CAD > Images.
Select an image (under Imported Files in the Project Explorer), right-click, and select Georeference Image from the context menu.

To geodetically position an image:

In the Plan View, zoom or pan to the general area in which you want the image to be located.
Right-click the image in the Project Explorer and select Georeference Image from the context menu. The Georeference Image command pane displays.
Click Add.
Pick a specific pixel that you want to correlate with a coordinate or control point in your project. The label A is added to the image in the view. The top, left corner of the image is pixel 0,0 (vertical, horizontal).
In the Point box corresponding to the A pixel, specify a coordinate. A line in the view indicates the direction and distance of the change / correlation that repositions the image.
Repeat steps 3 - 5 to create a B point. Two points position and rotate the image, if applicable.
Click Compute and review the mean square error (MSE) reported in the Results pane. With just two points the error will be zero. With more than two points, the higher the error, and the further each pixel is from its corresponding coordinate.
If necessary, add and compute up to ten additional pixel / coordinate pairs.
Click Close when you are done.

Image display styles

There are several options for controlling the appearance of images in the Plan View. These styles can be applied using the Display styles list in the Properties pane for an image:

Desaturated - Select this to remove all color from the image so it becomes a grayscale image.
Bluelined - Select this to turn black pixels into blue pixels.
The purpose of this filter is to convert a PDF plan that has a white background and black lines into an image that resembles a blue print (black background and blue lines). When used on a color photograph, the filter makes the image a bi-chromatic blue and black photo. If the image has a transparent background, you will not see it because it turns blue.
Inverted - Select this to swap each color for an inverse color.
Red,Blue,Green (RGB) color values range from 0 - 255 in intensity. The inverse color is calculated by subtracting the current RGB value from 255.
Dimmed - Select this to reduce the brightness of the image.

Each style modifies the original image, not a styled image. When images are styled, the changes are saved in the project.

Image transparency

You can specify the transparency of an image in the Properties pane for the image. In the Transparency box, specify a percentage (0 = opaque; 100 = completely transparent/invisible).

Scenarios:

If you need to edit the position of a georeferenced image, you can simply delete or change the pixel or coordinate of any pair.