Application Name: MapCalibrator
Description: Geocalibrates a map image using GPS positions, then plots your current position.
Publisher’s website: None
Version/date reviewed: v.1.06 / 7-20-11
Phone/OS: Droid X / Android 2.3
There are lots of apps (e.g. Locus, OruxMaps) that let you take previously-calibrated map images and then view your location on them using your phone’s GPS. MapCalibrator is a bit different – you can take a map image, either download from external sources on your phone, or photographed using the camera, and then calibrate it using three live GPS positions. After calibration, you can then view your approximate position on the map.
The program starts by asking you to select a map image for calibration. This can be a map picture you’ve uploaded to your camera, as with the topo map images above, or a photo you take with your phone’s camera. For example, you could take a photo of a trail from an info kiosk at the trailhead, then use the program to calibrate this map image.
I tried using map images in TIFF, GIF, PNG and JPG format. The TIFF format didn’t load at all into the program; the GIF and PNG formats loaded successfully, but I was unable to calibrate either of them. Only the JPG image worked correctly for me.
When you reach a known point in “real space” for which there’s a corresponding point on the map, you can add a calibration point. Press the Menu button, then select “New Reference Point”. A blue circle will appear in the map display, and you tap-and-drag that blue circle so that the center dot is on your current position. This can be a bit tricky, as your finger will cover the blue circle as you drag it, making it difficult to place accurately. The GPS is also not on continuously, so you’ll need to stand in one spot for about 15 seconds or so before calibrating, to make sure the program has your current position accurately.
Once you have the calibraiion point set, press Menu = Use Reference Point to save that calibration point. Your GPS coordinates are entered automatically, but if you have more accurate coordinates from a map or another GPS, you can enter them manually in degrees:decimal minutes format.
You’ll need to enter three calibration points in order to complete the calibration process. You can add additional points, but they won’t be used (though the program’s author indicates he might add the ability to use additional points in the future).
Once calibrated, your current GPS position is plotted as a red circle/dot on the map image. The GPS updates about every 15 seconds or so, so the position won’t always be up-to-date. In my tests, the calibration was pretty good, although the GPS position would sometimes jump to an offset position, then jump back again to an accurate position.
Other issues: The program doesn’t let you save image calibrations for future use, which is a big drawback; that means you’ll have to calibrate an image every time you want to use it. You should also remember that some maps are “schematic” in nature, i.e. scale, distance and direction may not be depicted with complete accuracy; such maps will be virtually impossible to calibrate accurately. You should try to use three calibration points that are spaced reasonably widely for the best results; if the points are too close together, the calibration is likely to be less accurate.
Final thoughts: In most cases, you’d usually be better off using apps like Locus or OruxMaps that allow you to use both online maps sources and your own calibrated maps. However, for those instances where the only map available is one posted on a bulletin board or info kiosk, MapCalibrator is a useful tool to have.