Getting started
by Alain Hoffmann

Let's assume you have a paper map in front of you. Best would be to have it professionally cut into sheets not larger than what your scanner can take which is letter size or A4 for "normal" users. Try scanning the map in 72 or 100 dpi resolution. Generally you don't need to go above 100 dpi but I sometimes find it better to scan at 200 dpi and have it reduced to final size by a good paint program (I like Paintshop Pro for this). Set the scanner to "color document" or "color photo" and high color (24 bit depth). Resize it first to the desired size, sharpen if needed and only as last step reduce colors to 256. I recommend saving them as GIF, PNG or TIFF, smaller maps can also be saved as JPG. Keep however always a backup of the scan in one of the first mentioned formats so you have a nice clean base to return to should your map file get corrupted. Several maps can be fitted to one large map using freeware or shareware tools found on The Net.

Another option is to have the map professionally scanned. This is however an expensive way. If doing so have it recorded onto a CD-ROM and tell them to use TIFF, GIF or PNG as saving format. JPG always looses some details. This is maybe not obvious the first time you work with the map but after some alterations you will notice it.

Once you have scanned the map successfully you need to calibrate it. By doing this you add several attributes to the file, telling the program some coordiantes on the map. You do not need to enter the scale of the map. But you need at least the exact position of 3 points to calibrate. This is the most difficult part of all the procedure. So you either must go out, drive to some places, get their coordinates from your GPS and come back home again. Or, if you are very lucky you can use other mapping products to do this. The Mapsource datas from Garmin are precise enough for many european countries and for the USA.

But now let's see the calibration procedure step by step.

 

Click "Load" - "Load and Calibrate Map Image". A window opens where you choose your map file. (The trial version only allows .BMP files, the full version almost almost all graphic files).
A setup window with several tabs will open on the right side. Here you have all the datas needed. The default tab (right) shows basic information. Normally you don't need to do much adjustments here. Leave everything as it is for now.
Now click on "Point 1" to get the table for the first point (Right). The cursor changes to a crosshair and the field "Image Coordinates" shows a blue background.

Look for a good point in the upper left corner of the map. Of course it's not important where you start but you should place a calibration point in each corner as well as one near the center.

The point should be a road intersection, best are 2 major roads as those coordinates are probably more precisely recorded. Also it's better to choose a rectangular intersection as this diminishes the error rate.

Once you have decided for a point click on the map and the image coordinates will show up. You can still shift the point around using the "shift"-key and your cursor keys. Once satisfied you must tell the program where this point lies in reality. In the example at the right I got 49° 41',323N and 5° 58',851E. This is the all the real work that has to be done. Of course you can use Longitude/Latitude lines if they show up on the maps.

The culprit is in finding these coordinates. If you have a good map program like those rated above average in our digital maps section or if you use Garmin's mapsource it's quite easy. Just look for the same place, write down the coordinates and transfer them to this table. Watch out for putting in the correct N/S and E/W tabs or you will end up in a complete disaster. Oh, yes, take also care not to mismatch a point for a semikolon in the coordinates or they will not be accepted.

If your GPS has a different output format like D,DDDDD (all degrees) or D, MM, SS (Degrees, Minutes, Seconds) you must either change your GPS display (through setup) or in OE click "File" - "Configuration" - "Maps". Now you can change the display format in "Lat/Long Display". Just make sure you are working in the same map date (see above in the map "Setup" tag where it shows WGS84) as your map is in. For most WGS84 should work. While you are in the configuration menu also alter the "Region" setting just above the "Lat/Long Display" to set it to your region. That way you will not be bothered by wrong N/S and E/W tags in the future.

Now repeat this step for each other corner of the map. Watch out to select FIRST the next point tab or you will erase the work you just did so painfully. In fact you theorhetically need only 3 fixed points if the map is exactly North/South and not distorted. In everyday use however go for 4 or 5 points if possible. Remember: the more precise your calibration the better the precision later on.

Special case: Distorted map and pictures taken from airplanes. Both can be used but need considerably more calibration work. You will find more help on this in the excellent help-section in OE. In my experience air pics are no big problem. Difficulties start if you want use a map from a book where the inner borders are bending upwards. Here the best way is to calibrate them JUST ON BORDER OF THE FLAT PART (before the distortion starts). This works surprisingly good even on the distorted parts. Putting the calibration points over the bend and into the distorted segment will disturb ALL the map. This also shows the importance of a clean scan. If you get new maps and bend them carefully flat you get an almost good map. Older and larger maps are harder work. This proves what all surveyors tell you: never fold a map.

Right: See where the calibration points should be placed? Sometimes this will not be possible as on maps with ocean squares. Those need even more calibration work to become accurate.

This is about all you need to do. Once you have found a satisfying number of points click on the "Save" button. You are now prompted for where to store the mapfile. You can do this in the same directory as the map lies in as the new file is a very small one. It just holds the coordinates you typed in.

That's about all and your map is now ready for use. Check the section on "How to connect the GPS" and it should show right up on the map (if your position IS on it).

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