Select Point ToolWhen an image is first imported to WMS, the image must be "registered." Registering an image involves identifying two or three points on the image corresponding to locations with known real world (xy) coordinates. Once these points are identified, they are used by WMS to stretch or map the image to the proper location when it is drawn with the other objects in WMS in the Graphics Window. If an image is not registered properly, any objects which are created using the background image as a guide will have the wrong coordinates.
An image is registered using the Register Image dialog. This dialog appears automatically after opening an image that is not auto-georeferenced. It can also be accessed using the Register Image command when right-clicking on the image in the Project Explorer.
The main feature of the Register Image dialog is a large window in which the image is displayed. Registration points (shown by "+" symbols) are also displayed in the window. These points are used to identify locations with known real world coordinates. The points are moved to the desired locations on the image by dragging the points using the tools to the left of the image (described below). Once the points are located, the real world coordinates can be entered in the edit fields shown below the image. Either two or three point registration can be used.
The Single Point Conversion command in the Edit menu can be helpful if you know the geographic (latitude/longitude) coordinates and want to convert to planimetric coordinates, or generally in converting between any two coordinate systems. You should perform this conversion prior to entering the registration dialog.
The Import World File button can be used to automatically define the registration data. A world file is a special file associated with a previously registered image that is exported from another program such as ArcView® or Arc/Info®. The file contains registration data that can be loaded into WMS and used to register the image.
The following tools can be used to help position the registration points:
The Select Point tool is used to select and drag register points to a location on the map for which real world coordinates are known so that they can be entered in the corresponding XY edit fields.
In some cases, it is useful to magnify a portion of the image so that a registration point can be placed with more accuracy. The Zoom tool is used to zoom in a portion of the image.
After zooming in on a portion of the image, the Pan tool is used to pan the image vertically or horizontally.
The Frame macro is used to automatically center the entire image within the drawing window of the dialog after panning and zooming in on a specific location.
After an image is imported and registered, the registration data are saved to a WMS image file as part of the project. The image file includes the path to the file containing the image file (TIFF, JPEG, etc.) image, the coordinates of the three registration points, and the XY limits of the currently resampled region.
After saving an image file as part of a project, when the project is read back into WMS, the image file is read, the associated image is opened and the image is registered and resampled. Thus, the image is automatically restored to its state just prior to when the project was saved.
Related Topics:
Importing an Image
Images
