The same calibration technique described in the section Calibrating raster images applies to scanned maps. Maybe the most common difference is that while calibrating maps we can use regular networks of reference points more often than for other types of drawings.

Open hberg.tif file and Zoom window around its left lower corner, so that the coordinates written there are legible, as shown below.

Click the Move raster button. Pick the left lower corner of the map as base point and type Tab 3476100 Tab 5476200 Enter to provide coordinates of target point . Again, this is just a preliminary move which precision does not have any influence on the calibration results, so no snapping or Magnifying Glass is needed. Choose the OTM - Accept option to complete the Move raster operation.

Click the Zoom extents button to show the entire map again, and the Calibrate raster button to show the Calibration toolbar.

Push the Define net button on Calibration toolbar and type in the Calibration Net dialog parameters describing a reference network corresponding to coordinate marks printed on the map as small crosses:

Push the Create button and check if the created net looks as on the picture above. In this zoomed-out view, it goes practically right through the marks.

Push the Add net-based vectors button on Calibration toolbar. The CALIBRATOR zooms automatically around the first corner of the defined net with the calibration vector attached to it; i.e. having the target location already defined.

Since the coordinate marks on the map have the regular form of small raster crosses, we are going to use raster snap to intersection. Choose the Options – Configuration option and check the Snap to raster active and Intersection of raster lines on the Snap tab. On the Magnifying Glass tab check the Magnifying Glass active , Verify every snap trial and Keep on display options.

For each target define corresponding Raster point by clicking the snap cursor at the corresponding coordinate mark and accept it with a right click. You may use Set options button on Calibration toolbar to change the AutoZoom level , if necessary.

Magnifying Glass pops up for every snapped coordinate mark (intersection) and provides instant visual verification. Do not correct errors smaller than half a pixel - it does not have any statistical meaning and often is very subjective. Correct only those points that are obviously wrong, usually due to interference of some other lines with the cross mark, as shown below. You should need to correct no more than 5-6 snaps. Only at one point Raster snap will not find the intersection at all, so you must pick the correct point manually.

Simply pick a new position for the snap cross in the Magnifying Glass window and accept with usual right click.

After defining Raster points corresponding to all 56 Target points of the net, push the Toggle vector list button to show the Raster Calibration Results dialog presenting complete, sortable numerical information concerning this calibration operation. Choose the Bicubic model using buttons on Calibration toolbar and check that Sqrt of mean square error that will remain after calibration is in the range of 0.219m (in world coordinates).

You may push the Toggle preview button and scroll through the list of Raster and Target points in order to evaluate visually differences between requested Target points and Calculated points depending on the Calibration model you choose. If you need to change something, you may delete points from the list or drag the red grip on the beginning of given calibration vector and correct it if necessary.

When using Calibration models higher than Bilinear, you must look at the calibration preview before executing it. Insufficient or badly selects calibration data, e.g. colinearly placed Target points , may result in perfectly small residual error and very bad deformation of the raster image between calibration points. Push the Zoom extents button and switch on the Toggle preview button. Calculated net should show only small and smooth deviations from the Reference net , as shown below. To check or change calibration nets colors push the Set options button on the Calibration toolbar.

When you are satisfied with the calibration preview, click the Execute button (or choose the OTM Execute option) in order to have the transformation applied to the image data. You may save the calibration report if you wish. After the calibration is executed, you may still keep the Raster Calibration Parameters dialog on the screen in order to examine the results by scrolling through the list of calibration vectors. If you want to get closer to some point, click at the Zoom in button on Main toolbar. Then use Undo and Redo buttons on Main toolbar to see that point before and after calibration. If you keep your Toggle preview button pushed, you should see that the Raster point is being moved by calibration to the end of the Calculated vector . To check or change calibration vector colors, push the Set options button on the Calibration toolbar.

Finish the calibration process by clicking the Accept button on the Calibration toolbar or choose the OTM Accept option. Optionally you may save the calibration vectors on file but, if you plan re-using them, remember to save the raster file just before doing the calibration, so that you may repeat the process using the saved vectors.

You may still Undo and Redo calibration changes from the Main toolbar. If you want to be able to repeat this exercise without reinstalling demo files, exit SuperEdit without saving the modified raster file, or choose the File - Save As.. option and give it a new name.

Zoom window around the left lower corner of the map, as at the beginning of this section. Snap to raster mark (intersection) at the left lower corner, as shown below.

All coordinate marks on the whole area of the calibrated map will show correct coordinates with accuracy better than 0.2 m in world coordinates. At 1:1000 scale, it means that the calibrated image accuracy is better than 0.2 mm across the entire map.