With Bentley Descartes it's possible to register images so they can be correctly located to a given coordinate system. This is done by warping them to fit a reference or base document. The base document can be an image, a vector file, a drawing, a map sheet, or a list of known points.
The first step in the register process is to place control points. Control points are locations on the image that typically represent a feature for which the world coordinates are known. This would include features such as the corners of a building, a road intersection, the edge of a property and so forth.
To obtain the world coordinates for a feature:
Note that the precision of the world coordinates are very important for the accuracy of the registration.
In preparation for placing control points, first define their locations by placing a marker at the location. For example, you can place red circles on the unregistered image feature to indicate that they are in an uncorrected location. Then place green circles on the corresponding locations using the read world coordinates obtained from the field, Google Earth or georeferenced document. The green markers represent the Base System while the red markers represent the Uncorrected System.
In the graphic below, the image needs to be registered to the vector map which is georeferenced correctly.
The Place Control Points tool can be used to position the points needed for Register to process the image. Pre-defining the locations of the points simplifies and streamlines this workflow.
To refine the registration and/or ensuring that the image lies accurately over the known features, you can move or delete any control point during the registration process.
The register process requires you to select the model that could be best used to transform the unregistered image. This selection is made in the Register dialog which is also where you can manage the quality of the control points.
After defining the control points and choosing the correct model for the registration process, the last step is to resample the image which is done using the Resampling dialog.
Productivity Tip : Since the resampling can be time consuming and CPU instensive, it is advisable to group resampling tasks together and process them during off hours.