GPS for Dummies.pdf - Engineering Surveyor

Chapter 15: Creating and Using Digital Maps with OziExplorer251The shareware version of OziExplorer can load only BMP images. Becausebitmaps aren’t compressed, the entire file must be loaded into memory,which can slow down the performance of computers that don’t havemuch RAM.Step 3: Calibrate the mapAfter you scan, edit, and save your map, one more step is left before you canstart using the map with OziExplorer. At this point, your map is simply a graphicsfile. 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 totake advantage of OziExplorer’s features.This involves calibrating the map, which involves linking georeferenced datawith the map image so that each pixel in the map has a geographic coordinateassociated with it. When a map has georeferenced data, you can Move the cursor on the map, and OziExplorer will accurately report thecoordinates of the cursor in latitude and longitude or UTM (UniversalTransverse Mercator; read more about these in Chapter 2). Draw lines on the map to measure distance. Calculate the size of areas. Track and display your current position on the map when the computeris connected to a GPS receiver. Transfer GPS waypoints, routes, and tracks between the map and a GPSreceiver.When you calibrate a map with OziExplorer, the georeferenced data isn’tembedded directly inside the image file. OziExplorer creates a separate MAPfile (.map) that contains the following information: The location of the map image file The map datum The map projection Map calibration dataInside a MAP file, the file is in text format and can be viewed with any wordprocessor.Calibration requires you to identify a series of points on the map with knowncoordinates. Depending on the number of points that you select, as well asthe map datum and projection, OziExplorer performs different mathematicalcalculations to link coordinate information with the map image.