Autodesk 00126-050008-1640A User Guide - Page 58

5 Calibrating Raster Images To create calibration pairs: 1. Specify the known theoretical point coordinates (real points). There are two ways to do this - define a calibration grid or add them one by one. Both methods may be used simultaneously. Upon creation, each calibration pair has the same measured and real point coordinates. 2. Specify the appropriate measured points for all real points by picking them on the image or entering the point coordinates from the keyboard. Defining Calibration Grid A calibration grid is helpful when calibrating images covered with the raster grid with nodes that must have known coordinates. Such images are, for example, scanned images of maps or geodetic plans. Defining a calibration grid creates a set of calibration pairs placed in the nodes of a rectangular grid. These calibration pairs have the Grid type. The position of grid nodes is determined by the origin, angle, cell size and the number of cells in the vertical and horizontal directions. Þ There can only be one grid defined on the image. Redefining a calibration grid removes all calibration pairs of the present grid from the image. To define a calibration grid 1. Open the Calibration dialog box. 2. Click the button in the Calibration dialog box. The Calibration Grid dialog box appears: Calibration Grid dialog box 3. Specify the grid origin. Enter its coordinates into Origin, or press the Measure button and click the origin location on the image. The grid origin is assumed to be in the lower-left corner, and the grid is generated along the positive direction of the X and Y axis. To set a different corner and grid direction, set negative values in Size and Cell boxes. 4. Specify X Size and Y Size of the grid cell. 59