OziExplorer supports a number of different digital map types that use georef-erenced data (information that allows a program to precisely identify locations and coordinates on a map). But one of the program’s most powerful features is its ability to turn your own graphics files into georeferenced maps. This means if you have a paper map, you can scan it, load it into OziExplorer, and effectively make it an electronic (digital) map. This is a three-step process:
1. Scan the map.
Use a scanner to create a digital image of the paper map. Stitch individual map pieces, if necessary.
2. Edit the map.
Make changes to the scanned map before it’s used.
3. Calibrate the map.
Load the edited map into OziExplorer and associate georeferenced data with the map image.
The following sections explore the above three steps in further detail.
Scanning and calibrating your own maps can be fairly time consuming and sometimes frustrating if you can’t seem to get the map coordinates to match up with reality. Some maps are definitely easier to calibrate than others. If you’re not technically inclined or are somewhat impatient, you’ll probably want to stick to importing maps that are already georeferenced, such as freely available United States Geological Survey (USGS) DRG topographic maps.
Step 1: Scan the map
The first step when converting a paper map to a digital map is to scan the map and turn it into a graphics file. You don’t need an expensive, high-end scanner to accomplish this task; most any color scanner will work.
If you want to scan a large map — say, anything bigger than a legal size piece of paper — consider literally cutting it up into pieces that will fit on your scanner. (8.5 x 11 inches works well.) Instead of using a pair of scissors, use a paper cutter, such as those found at copy centers, to ensure that you end up with straight cuts. The straight cuts are important for accurately aligning the map on your scanner. Although you can scan a large map one portion at a time without cutting it, it’s more of a challenge to get the edges lined up when you stitch them together as I discuss next.
Here are some tips to improve your map scanning:
Use medium dpi: Scanning the map between 125-200 dots per inch (dpi) is good enough; you don’t need to scan at higher resolutions typically used for reproducing photos.
Use color photo scanning: Most scanning software has different settings for different types of documents you want to scan, such as text, line drawings, and photographs. Select the color photograph option to retain the most detail. However, remember that most maps don’t have millions of colors like photographs, so if your scanning software supports it, use a 256-color setting.
Watch edge alignment: Place the to-be-scanned map directly on the scanner, ensuring that the edges are aligned directly against the scanner bed with no gaps. You need to keep the paper map as square as possible to reduce distortion during a scan.
Prevent edge distortion: To help keep the map edges pressed flat, leave the scanner cover open and use a topic or something heavy to set on top of the map. The edges are typically where the most distortion occurs during scanning because they tend to lift up.
Experiment with settings: Try a couple of experimental scans first, changing the brightness and contrast settings. If you’re going to be scanning a number of maps over a period of time, write down the settings that gave you the best output so you can use them next time.
Save the final scan as BMP: When you’re ready to produce a final scan of the map, initially save it as bitmap (BMP) format file. This produces an image that’s as close to the original map as possible; bitmap files aren’t compressed like JPG and other graphics file formats. Bitmap files do take up a lot of memory and disk space, but after you edit a file, you can save it as another graphics format that’s smaller in size.
OziExplorer and World War I
The 1980s movie Gallipoli recounted the Australian experience of fighting the Turks during World War I. Although long before the time of computers and mapping software, WWI also has a link to OziExplorer.
Howard Anderson wrote a fascinating article on using OziExplorer to locate old World War I trench lines in France and Belgium. The remains of the trenches are long gone, but by using old maps from the period, scanning them, and adding georeferenced data, Anderson was able to clearly determine where the trenches were dug during the early 1900s.
After he had scanned and georeferenced the old military maps, Anderson used OziExplorer to draw GPS tracks on personally created digital maps to trace the outlines of the trenches. He also used waypoints to identify military and land features. Anderson then took the tracks and waypoints and overlaid them on a modern map in OziExplorer. This revealed where the long-ago war emplacements once stood. Anderson’s last step was to visit France with a GPS receiver and his old and modern maps. He found that, with relative accuracy, he could stand on the site of a trench where his grandfather had fought over 85 years ago.
If you have a map that’s made up of multiple image files, such as a large map cut up into a series of smaller maps, you’ll need to stitch them and a single, large image. Commercial graphics program such as Adobe Photoshop and Jasc Paint Shop Pro have commands for combining files. You can also manually stitch together images with Microsoft Paint by using the Paste From command of the Edit menu. Here’s a link to a great tutorial on stitching together scanned images: www.sibleyfineart.com/index.htmTtutorial-join-scans.htm.
Step 2: Edit the map
After you successfully scan the map, make any last-minute changes to the image. This could include
- Adjusting the brightness and contrast to make the map more readable.
- Adding symbols or text information.
- Removing the white space (or collar as it’s known in map-speak) that surrounds the map.
Use your favorite graphics program to make any final edits to the map image. After you’re through, save the map as a TIFF, PNG, or JPG file to reduce how much disk and memory space the image takes up. (These compressed file formats are more space-efficient and memory-efficient.)
The shareware version of OziExplorer can load only BMP images. Because bitmaps aren’t compressed, the entire file must be loaded into memory, which can slow down the performance of computers that don’t have much RAM.
Step 3: Calibrate 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.
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.
FUGAWI
FUGAWI is a popular Windows mapping program with some of the same basic features as OziExplorer.
Like OziExplorer, FUGAWI can read a number of different map formats with georeferenced data as well as use do-it-yourself, calibrated, scanned image maps. The program can also interface with a GPS receiver and handle waypoints, routes, and tracks. See a FUGAWI map in the figure here.
Comparing FUGAWI with OziExplorer, you’ll see that FUGAWI isn’t shareware, it’s priced a little higher, and it comes bundled with a base set of maps.
FUGAWI and OziExplorer both have extremely loyal user bases. If you check around the Internet, you’ll see some strong feelings expressed about why one product is better than the other. (I think
OziExplorer has a better user interface and supports a few more advanced features.) If you’re considering FUGAWI or OziExplorer, download the free demo versions of each program and see which one you prefer.
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.
Choosing calibration points
To associate georeferenced data with your scanned map, you’ll need to find a series of points on the map with coordinates you know. If you can’t assign a latitude and longitude (or UTM) position to a few features on the map, you won’t be able to calibrate the map.
Here are some ways in which you can pick calibration points:
If the scanned map has a collar with coordinates printed on the edge, use the coordinate marks. USGS topographic maps are easy to calibrate because each corner is marked with the latitude and longitude.
Use another mapping program to get the coordinates of a feature on a map that you want to calibrate. This can be a man-made feature (such as a building or a bridge) or a natural feature (such as a mountain peak).
If you’re in the United States, you can use National Geodetic Survey datasheets to identify points on the ground that have known coordinates associated with them. Visit www.ngs.noaa.gov/cgi-bin/datasheet. prl to access datasheets for your area.
Visit a location that’s clearly identifiable on the map, and use your GPS receiver to record the coordinates for that location. Road intersections make good calibration points. (Just watch out for traffic!)
The number of points that you select for calibration depends on the map and how much accuracy you want. Use the following guidelines to determine how many points you should use:
Two points: If you’re limited to two calibration points, select two points at opposite corners of the map. (This is the only calibration method available in the shareware version of OziExplorer.)
If you have a registered version of OziExplorer, always choose at least three calibration points, such as three corners of a map.
Three or four points: Selecting three or four points (such as the map corners) provides better map accuracy and should be all you need for calibrating most maps.
Five or more points: If the latitude and longitude lines are curved, if the paper map has been folded, or if the scan of the map is distorted, use more than four points. OziExplorer supports up to nine calibration points; generally, the more points you choose, the better the accuracy with any map that might have distortions that could impact accuracy.
Try to spread your calibration points out over as much of the map as possible. If you clump the points together in a small area, the accuracy won’t be as precise.
After you look at the map and determine which calibration points you’re going to use, write down the coordinates and then double-check that they’re correct. Entering calibration points with incorrect coordinates is a common cause of map accuracy troubles.
In Figure 15-2, the example USGS topographic map was scanned in pieces, stitched, and then saved as a JPG file. The original paper map had the latitude and longitude coordinates in all four corners, so I use these coordinates as the calibration points. (This map is too large to reproduce here, so note that you can see the coordinates only in the upper-left corner.)
Figure 15-2:
Corner coordinates on a map make good calibration points.
Setting calibration points
After you decide which points you’ll use to calibrate the map, load the map image file into OziExplorer and do some georeferencing. Here are the steps to take:
1. Select Load and Calibrate Map Image from the File menu; a file dialog box is displayed.
2. Select the location of the map image file and click Open.
The map appears in a setup window, as shown in Figure 15-3.
Figure 15-3:
The OziExplorer setup window with a loaded map.
3. Enter the map’s name, datum, and projection.
Information provided on the example paper map says the datum is NAD 27 and the projection is Universal Transverse Mercator. Enter those values.
If you don’t know the map datum, make an educated guess or use WGS 84. If you don’t know the map projection, try using Latitude/Longitude. Both of these settings can be changed later if they end up incorrect.
Entering the wrong map datum and projection can severely affect the accuracy of your map. If you don’t know the datum and projection, your best bet when calibrating the map is to match coordinates that you recorded with your GPS receiver to features that you can clearly identify on the map; then use the WGS 84 datum and Latitude/Longitude projection.
4. For each calibration point (up to nine points), repeat the following steps:
a. Click the point’s tab in the setup window.
b. Move the cursor on the map over the point.
Figure 15-4:
The first calibration point setup window.
The cursor turns into a cross-hair icon with the number 1 next to it. A zoom window shows a magnified image of the cursor location allowing you to precisely place the cursor over the calibration point.
c. Click the left mouse button to select the calibration point.
A bull’s-eye appears over the calibration point.
After the bull’s-eye appears onscreen, you can move the calibration point to a new location by holding down the Shift key and using the navigational arrow keys. This gives you a fine level of control over placing the calibration point.
d. Enter either the latitude and longitude or the UTM coordinates for the calibration point.
OziExplorer expects the latitude and longitude coordinates to be expressed in degrees and decimal minutes. If your coordinates are in another latitude and longitude format, you can quickly convert them at this Web site: http://jeeep.com/details/coord.
5. When you’re finished, click Save.
OziExplorer prompts you for a name and where to save the MAP file. You’re now ready to start using your imported map. The example scanned-and-calibrated map being used with tracks and waypoints is show in Figure 15-5.
Figure 15-5:
A scanned and calibrated OziExplorer map with waypoints and tracks.
Maps that are made for general information purposes are usually difficult to calibrate correctly because they don’t have the level of accuracy as navigation or survey maps do. (In fact, they’re more of diagrams — not maps — because they don’t have projections.) The actual locations of features shown on the map might not be correct, and distances and proportions might not be accurate.
Checking your Work
After you load and calibrate a scanned map, always check to make sure that your calibration was correct. Here are some ways to do this:
Select Grid Line Setup from the Map menu. This allows you to overlay latitude and longitude grid lines over the map. The overlaid grid lines should match with the grid lines on the map or the coordinate marks on the map edges.
On USGS topographic maps, don’t get latitude and longitude lines confused with the more predominant Township and Range lines.
If your scanned map has a ruler printed on the map that shows distance (for example, in one-mile increments), select Distance Display from the View menu. This allows you to measure the distance of a line that you draw on the map. The length of the map’s ruler should match whatever distance is shown when you measure it.
Move the cursor over a feature on the map with known coordinates. (The coordinates can come from a GPS receiver, another mapping program, or a gazetteer.) The cursor coordinates in OziExplorer should be relatively close to the known coordinates of the feature.
If any coordinate or distance numbers seem significantly off, there’s likely a problem with your calibration. To address this, do the following:
1. Choose Check Calibration of Map from the File menu. This displays the calibration setup window.
2. In the calibration setup window, verify or change calibration data.
• Make sure that your calibration points are in the proper location on the map and have the correct coordinates.
• Try changing the map datum and/or projection to different values.
3. Click Save to save the results to a different MAP file.
The newly calibrated map is loaded and is displayed onscreen.
4. Check whether the calibration is more accurate.
If the calibration isn’t sufficiently accurate, repeat these steps.
