Before a scanned map can be displayed in the correct location, it needs to be calibrated (geo-referenced). This process involves specifying the location of two known points on the map. Once the correct geographic coordinates are known for these points (called Calibration Points), ExpertGPS can calculate the coordinates of every other point on the map.
Before you can use your map in ExpertGPS, it must be added to the Map Library and calibrated.
To add a new map to the Scanned Map Library, clickon the , under .
The Open Scanned Map dialog will appear. Select a JPEG, TIFF, PNG, or Bitmap image of your map.
In the Edit Scanned Map dialog, enter a descriptive name for your map, and specify the projection information located on the collar of your map. If your scanned map came with a calibration file (worldfile or map calibration file), it will automatically be detected and used. Otherwise, you will need to manually calibrate the map so that your GPS data appears correctly on it.
Once you've named your map and selected a projection, you can skip ahead to calibrating your scanned map.
In order for your scanned map to display correctly, ExpertGPS needs to know the details of the projection used when the map was printed. This information should be printed in the margin or a corner of your map.
Enter the latitude of the two standard parallels, in degrees and decimal minutes.
The standard parallels for maps showing all 50 US states are typically 20º and 60º North.
The standard parallels for maps showing the 48 conterminous US states are typically 29º 30' and 45º 30' North.
Enter the longitude of the central meridian. This is the only line of longitude on the map that is vertical. All other meridians are at an angle.
If the Central Meridian is not explicitly listed in the map margin, determine the line of longitude that is vertical on the map. In the example below, the 0º and 20º East lines of longitude slope away from the vertical at the same angle. Therefore, the vertical Central Meridian lies halfway between them, at 10º East.
Enter the latitude of the natural origin of the map.
Enter the false easting used by this projection.
Enter the false northing used by this projection.
Enter the scale factor at the natural origin of the map.
Once you have selected a new scanned map and specified its name and projection in the Edit Scanned Map dialog, the uncalibrated map will appear in the Map window in ExpertGPS. Because the map is not yet calibrated, it will appear in the wrong location, relative to the GPS data in the file. You will now add calibration points to the map, which will "anchor" a specific landmark on the map to its correct geographic coordinates. ExpertGPS needs two calibration points to properly fit your scanned map to its correct location on the Earth.
To create a calibration point at a grid line intersection, click with the Calibration Point Tool over a point on the map where you know the correct coordinates.
The Edit Calibration Point dialog will appear. Enter the coordinates, and click .
To use a waypoint as a calibration point, hold down the Shift key and click with the Calibration Point Tool over a feature on the map which corresponds to a waypoint in the file. (a mountain summit, the trailhead parking lot)
The Select Waypoint dialog will appear. Select the corresponding waypoint, and click .
If you have GPS waypoints, a tracklog, or shape data that matches with features on the scanned map, you can drag them into position on the map. Switch to one of the Calibration Point Tools, and move the mouse over a piece of data on the map. Click and hold the mouse, and drag the data to its correct location on the scanned map.
The cursor will change to . Set the second calibration point using one of the three techniques above. For best results, set the second calibration point on the opposite side of the map from where you set the first calibration point. Once you have set the second calibration point, you should see that the rest of your data now lines up nicely with features on the scanned map. You can switch between the two calibration point tools to make final adjustments to the map calibration.
The Keep Scanned Map Calibration Changes dialog appears. If you are not satisfied with the calibration point changes you just made, you have the option to discard them.
Your scanned map is now calibrated and ready for use. The next time you want to view GPS data over this map, clickon the .