Calibrating the map

After you scan, edit, and save your map, one more step is left before you can start using the map with OziExplorer. At this point, your map is simply a graphics file. You can use Microsoft Paint or any another graphics program to view, edit, and print the map, but you want to turn the image into a smart map to take advantage of OziExplorer’s features.
This involves calibrating the map, which involves linking georeferenced data with the map image so that each pixel in the map has a geographic coordinate associated with it. When a map has georeferenced data, you can

• Move the cursor on the map, and OziExplorer will accurately report the coordinates of the cursor in latitude and longitude or UTM (Universal Transverse Mercator)
• Draw lines on the map to measure distance.
• Calculate the size of areas.
• Track and display your current position on the map when the computer is connected to a GPS receiver.
• _ Transfer GPS waypoints, routes, and tracks between the map and a GPS receiver.

When you calibrate a map with OziExplorer, the georeferenced data isn’t embedded directly inside the image file. OziExplorer creates a separate MAP file (.map) that contains the following information:

• The location of the map image file
• The map datum
• The map projection
• Map calibration data

Inside a MAP file, the file is in text format and can be viewed with any word processor.
Calibration requires you to identify a series of points on the map with known coordinates. Depending on the number of points that you select, as well as the map datum and projection, OziExplorer performs different mathematical calculations to link coordinate information with the map image. To demonstrate the process of calibrating a map with OziExplorer, use a scanned copy of a 1:100,000 scale USGS topographic map Some digital maps have georeferenced data embedded directly into the map image as tags or come with associated files that contain the reference data. (A common example is a DRG map.) OziExplorer can use these maps without going through the calibration process that I describe next. Check the OziExplorer Web site or the program’s online help for a full list of these supported map types.