Raster Map Import and Calibration
Overview
This dialog can be found in ‘Menu-Map-Management-Recalibrate Map’ and in ‘Menu-Map-Management-Import Map’.
It allows to convert (import) an arbitrary image as map. And existing raster maps can be re-calibrated here. In contrast to a vector map the raster map is basically an image that contains additional attributes in order to use it as geographic map.
During calibration known points will be placed on the image. ‘Known’ means that a landmark or point of interest is clearly identifiable in the image and that its exact geodetic position is known.
Image Import
As suitable image can server an aerial photo or a scanned map. At least 4, better 5 to 8 prominent points on the image should be recognizable and their position must be at hand.
1. Open the image
Press ‘Open Image’ and choose an image.
2. Chose Approximation
Leave the combo-box ‘Approximation’ unchanged, a polynomial approximation of degree one () is good enough in most of the cases. Using an approximation the calibration algorithm converts the reference points into a mathematical formula. The formula is saved with the image and can later be used in order to convert pixel positions in the image into geodetic coordinates and vice versa.
Higher degree approximations be more precise but require more reference points.
3. Set Reference Points
Once the image is open left-click into the image and mark the known points prepared above as precisely as possible. For low-zoom images - like a world or country map - cities are good references. In images with a lower scale or higher resolution street junctions, landmarks or an antenna mast can be used. Once the reference point is placed a pop-up dialog requires the input of the geodetic (map) coordinates. If the position is not known but the reference point is accessible in the real world it could be an option to locally determine the coordinates using a GPS device.
Use mouse or keyboard in order to zoom or move the image and to set the reference points more precisely.
| Mouse | |
| left button click | set reference points |
| left button double click | edit reference points |
| left button press and hold | move reference points |
| middle button press | move map |
| mouse wheel | zoom in/out |
| Keyboard | |
| Cursor keys | move map |
| +/- key | zoom in/out |
4. Remove Reference Points
Drag the point and drop it out of the image area. Press ‘Clear Points’ in order to drop all points.
5. Refine the Map
If there is a GPS-track at hand it can be used to load the trackpoints or waypoints as reference points.
Leave this dialog open and switch to the FancyRoute main window. Load or create the track (just a few points), then copy the track to the clipboard. Switch back to this calibration dialog, press ‘Refine’ and paste the track just copied as blue reference points into the image. Then move these blue points to their proper position. They turn red then.
Throw the redundant, blue points away by pressing ‘Clean up’.
6. Save the Map
Press ‘Save Map’ in order to permanently save the calibrated map. Then this dialog can be closed
Image Re-calibration
Maps that have been created by image import or image download can be re-calibrated by using this dialog. The procedure is exactly the same.
Tips
Press the calculator symbol in the top right corner of the dialog in order to pre-calculate the expected map scale.
Calibration Preferences
In ‘Menu-Options-Preferences-Calibration/Download’ several options can be arranged for the map calibration.
