Map Calibration

Before you can use your GPS on a new map, you must calibrate the map.  This is so that map2hand understands the area of the world that your map represents.

In order to calibrate a map, you will need to know the geographic location of at least two points on the map.  These points should be well separated on both the horizontal and vertical axes (in order to minimise the impact of minor inaccuracies).  You will need to know the coordinates in one of the following systems:

• Latitude/longitude
• UK National Grid coordinates (as shown on Ordnance Survey maps)
• Universal Transverse Mercator (UTM) coordinates

Alternatively, if the map represents an area where you are currently located, you can use your GPS device to generate the coordinates for you (see later).

Some websites (e.g. multimap) are able to display the geographic coordinates of certain locations, so this is also an option.

Note that in order for map2hand to function properly, it is imperative that accurate calibration information is supplied.  map2hand understands nothing about the map that has been loaded – it is entirely dependent on calibration information.  Initial testing has shown map2hand to be highly accurate when supplied with a well calibrated map.  Calibration is a complex issue, and more detailed help will be provided in future.

Follow the procedure below to enter calibration points.

Ensure you are not in “full screen” mode (disable via the map2hand preferences screen).  This is a limitation of the current version of map2hand, and it anticipated that this will be resolved in a future release.

Select the map to be calibrated from the list on the main screen and tap the “View” button

Tap the icon at the top of the display, then select the “Calibrate” option.  The calibration screen is displayed (see right). Select the system (grid or lat/long) Select the projection (use UK National Grid for OS maps, otherwise use a suitable UTM system.  Note that if you chose lat/long as the system, you can tick “Auto-select” for the projection - this will select an appropriate UTM coordinate system, depending on the lat/long points that you enter when calibrating). Tap the “Calibrate” button.  The display will return to the map.

 

Use the stylus to drag the map until you find a location that you know the coordinates of in your selected calibration system. Select the  button from the top of the screen.  The button will invert (), and crosshairs will appear on the screen beneath the stylus (see left). Use the stylus to drag the crosshairs to the exact location of the calibration point Lift the stylus

A form will appear requesting the coordinates of the crosshair position.  If the crosshairs have not been accurately placed at the correct point, you can select "Cancel" and amend the position. If you know the coordinates of the crosshair location, enter these coordinates (the display will prompt you for them in the coordinate system that you selected on the "Calibration" screen above). Alternatively, if your GPS unit is attached and you have moved the crosshairs to the position on the map where you are currently physically located, then you can use the “Use GPS…” button to obtain the coordinates of the location.  When you select this option, the GPS unit will determine your current location, and will automatically fill in the fields with the coordinates of that location. Select “Done”

Repeat until at least two calibration points have been entered.  Note that to get good calibration across the whole map, it is advisable to choose locations that are as far apart as possible on both the horizontal and vertical axes.  This minimises the impact of minor inaccuracies in the location of the calibration points. 

You can get an overview of the separation of the calibration points using the "Show Points..." option, accessed via the "Calibration" screen.

Good. Calibration points well separated in both directions Bad.  Calibration points are too close on the vertical axis.  This will lead to inaccurate positioning in this direction Bad.  Calibration points are too close on the horizontal axis.  This will lead to inaccurate positioning in this direction

 

When two of more calibration points have been entered, select the button at the top right of the map to save and close.

See the Display/GPS section for a description of how to use the calibrated map to display your position.

Important note about calibrated maps

When you have calibrated a map, the calibration information is stored with the map (it is physically written into the map file).  It is not stored in the PalmOS handheld.  Once you have calibrated a map, the new file (including calibration information) should become your "master copy" of this map.  It is recommended that you save a copy of the calibrated map file back to your PC for future use.

Map images produced from the Ordnance Survey Get-a-map service.
Image  reproduced with kind permission of Ordnance Survey and Ordnance Survey of Northern Ireland