Edit Georeferenced Image

Description

Georeference an image so it can be used as a background to your vector data.

Access

Manage / Configuration / Georeferenced Image / Insert a new item or Edit selected item

Requirements

Image GeoRef module

Controls

Control	Description
Name	Type a name to identify the image.
Description	Type a description for the image.
Image	Shows the folder where image is stored.
Reference external image	Select the checkbox to keep the image external to the project. Note: Only ECW format images have the option of being referenced externally. All other formats are imported into the project.
Transformation	Select the transformation to apply to the control point coordinates.
	Add a new item.
	Delete the selected item.
Transformation Type	Select the transformation type to apply to the image. See Transformation Types table below.
	Show the image view.
	Show the model view.
	Clip the image using a rectangle.
	Clip the image using a free form boundary.
OK	Start the georeferencing process.
Cancel	Close without saving the changes.

Transformation Types

Type	Description
Conformal	Use when the image is based upon an orthogonal grid with minimal distortion. A minimum of 2 control points are required.
Affine	Use when the image is based upon an orthogonal grid but may have systematic scale and axis rotation distortion. Can also be used effectively where the image is based upon a latitude / longitude grid or for orthophoto map images. A minimum of 3 control points are required.
2nd Order Polynomial	Use when the image has distortions other than just uniform scale distortions in the X and Y directions and a rotation distortion between the X and Y axes. Can be used to remove distortions such as aircraft tilt in an aerial photograph, such distortions are systematic and apply over the entire image. A minimum of 6 control points are required.
3rd Order Polynomial	Used when more control points are available to achieve a better determination of the distortions. The same conditions apply to 3rd order polynomials as to 2nd order polynomials. Although the additional control points of the 3rd order polynomial will generally give lower residuals at the control points, this may be at the expense of accuracy between the control points, depending upon the image. A minimum of 11 control points are required.

Notes

Using a Conformal or Affine transformation on an image that has considerable distortion will not cause it to fail but will result in large residuals at the control points.
Polynomial transformations should not generally be used on an image where the distortions are essentially just scale and rotation. There are minimal errors in these types of images and the mathematics of the polynomial can become unstable and either fail or grossly distort the image.
Polynomial transformations cannot be used to remove random errors over an image due to terrain height distortions because these are not mathematical distortions and vary at any location in the image. They are best used on aerial photographs with minimal height differences across the image.
Ensure that the resultant transformed image is within acceptable tolerances at any location within the image.
Externally referenced image files that are no longer available at their original location should be placed in the Image folder. The location of the Image folder can be configured via General Options.