Version 3.2

Map Calibration for GPS usage

In order that a GPS receiver understood point coordinates sent to him, and vice versa, it is necessary to tell software what is the referential placed on the map (Scale tab). To achieve this, origin coordinates and axis length must be correspond to the map indications in a absolute way (geo-referencing). Scale placement in this context is mentioned in this document under the term of Calibration.
Note that a map calibration can be changed at any time without any information loss on the current route.

eMapZone accept several system for the calibration :

UTM system

eMapZone works with this system to memorise and save the coordinates of points, because they stand directly for meters. The UTM system (Universal Transverse Mercator) is a world-wide standard for geo-referencing, most of the GPS accept it, and, although its grid has one kilometre steps, even country used to statute (miles/feet) system use it. The UPS system is the UTM equivalent near the poles.

The earth is divided into 60 zones, the first one around the Bering strait :


For west to east : at the top, the sixty UTM zones ; at the bottom, the longitude on degree from Greenwich meridian.
From North to south : at left, the latitude in degree ; right, UTM letters (unused in eMapZone)
Thanks to
http://www.colorado.edu/geography/gcraft/notes/coordsys/coordsys.html

For calibration

Example :

This is a corner of a map with a UTM grid :

If the scale origin is place on the grid cross (there is little chance to set it here because X and Y axis will not fit, but this is just an example), map origin fields will be set with :

x = 680000
y = 4845000

© IGN

If you do not known the UTM zone, a technique is to enter at origin a value in dd°mm'ss'' (most of the maps mention at least one longitude in degree from the Greenwich international meridian), for instance -70°17'00'', and then to change to the UTM grid : the zone is automatically computed. Another technique is to read what's given from a GPS receiver if it is physically located on the map area.

Croix Lambert

This system is used with French maps from Institut Géographique National (IGN). Old IGN maps do not contain a GPS grid, so the Lambert system can be used for calibration. These maps are marked out with little crosses (croix = some "+"), evenly spaced at each kilometre. They are Lambert zone I II III or IV trailers. When this system is used, coordinates are shown, memorised and saved directly in this system.

Procedure

Example :

IGN map 1/25000 Top25 without GPS grid

If the scale origin is set on the "+" just under the Castelas word, these values must be set :

x = 864000
y = 3176000

Lambert zone is automatically detected = III

© IGN

Degree-minute-second

Some maps only contain degree references. In this case, the scale origin must be set on a meridian/parallel intersection and grid set to dd°mm'ss.s''. When this grid is selected, axis length must be set in this same format. Note that eMapZone always memorise and save UTM data for its internal management and computation. Note also that the software suppose that meridians and parallels fit on a straight grid. On the longitude axis, the reference is the Greenwich meridian. For west longitudes, enter a negative sign "-" before the degree value. The map datum should be indicated on the map itself.

Procedure :

Datum

The Datum stands for values needed for projecting computation and referencing of coordinates on the globe (ellipsoid, Tx Ty Tz...). In general, the WGS84 datum is a standard because this is the system that GPS satellites use. But it is preferable to check map information where the used datum should be indicated.

Grid checking

The Grid... button at the bottom of the scale panel gives access to a window allowing to move the scale with a result viewing on the whole map. It is possible to zoom/unzoom during its use. When this window is visible, a red grid corresponding with the used scale is drawn on the map, and the different buttons can change it :

Usage advice

Beware, the scanned map can present deformation, its flatness can be altered, it is sometimes difficult to get a homogeneous result. Try to do the best near the route itself. Results with a GPS receiver are most of the time quite precise.

Default GPS system in Options

In the Options tab, it is possible to set what are the GPS system to use when creating a new document. At the first use of the software, the UTM zone is computed from the current time zone. This computation is an approximation because there are 24 time zones and 60 UTM zones. The correct value should be set.

Data Transfer with a GPS device

The GPS dialog box is accessible from the GPS, Transfer data menu. The window contains tabs on the left for settings and actions, a list for transfer result, a state panel at the bottom and arrows for data stream changing colour during communication. This window is sizeable.

When window is shown, eMapZone checks that the map calibration has a correct GPS reference. Otherwise, a warning is shown on the state panel.

General Tab

In order to check that the device is correctly connected and recognised by the software, settings must be specified :

LOG Tab

The LOG is the record of successive positions of the receiver in a continuous way, also called Track. With eMapZone it is possible to get this record back from the GPS in to see the trip, on the map, where the receiver was. With a Garmin receiver, it is possible to send a LOG to the GPS in order to follow it exactly as it was drawn on the map with eMapZone.

Note that the LOG is made of points containing less information than Waypoints (see next tab), so it will be necessary to proceed in two steps to send or get real waypoints.

GPS -> eMapZone

This panel allows to get the LOG from the GPS :

  1. Click the Read LOG button. Point coordinates are shown in the list during the reception

  2. The Validate and Close button is activated at the end of the transfer. It will close the window and show the LOG on the current map.

Notes :

eMapZone -> GPS

This transfer is only possible with Garmin GPS (its a Magellan limitation). The Send Log button :

Route/Waypoints Tab

GPS -> eMapZone

This panel allow to get Waypoints from the GPS touching the current eMapZone route. That's why a route document must be present in the software (otherwise the Read Waypoints button is not active).

  1. Click the Read Waypoints button. The list shows the waypoints read from the GPS.

  2. If at least one waypoint was read, the Validate & Close button is activated at the end of the transfer. Click on it : the window is closed and the waypoints close to the current route are inserted in it.

Typically, this transfer should be done immediately after the LOG transfer to get Waypoint entered during GPS usage on the recorded itinerary.

GPS -> eMapZone

With this panel, it is possible to :

Sent waypoints can be :

Notes :

Examples

Follow your GPS

Prepare a itinerary with eMapZone and be guided by your GPS on the field. Follow these steps :

  1. Prepare the itinerary with eMapZone. Try that point names are not duplicated, remember to name intersections, forks... Anyway, those waypoints are not stored inside the GPS for its whole life : it is very easy to delete them later (by symbol).
  2. Check map calibration
  3. Send the LOG to the GPS after having deleted the one present in the device. Verify the maximum track log points. The GPS will then contain the trip track, without waypoints.
  4. Send Waypoints to the GPS (only those with a name)
  5. On the field, choose the "map" display : the track will be shown on the GPS screen, with named points. During the moving, just try to keep along the track (very easy ; for biking, try to fix the device on the handlebars).

Another possibility is the send a route to the GPS ; this option is less precise because the route is made of named waypoints, without intermediate points, and most of the time the total number is limited. Interest : the GPS gives you the directions and you can stored many routes. But note that you can choose to "track-back" the active log : a route is automatically generated.

Make an itinerary with data from the GPS

Another interesting usage : record moving on the field and see them later at home on you screen. Magic !

  1. On the field, start by deleting the LOG and activate its recording
  2. During your walk, it can be interesting to mark noteworthy point (point of view, picnic, fork, fall...) using the "mark" button
  3. At the end, think to power off the GPS.
  4. At home, plug your GPS and select the map ; check calibration.
  5. Use the Read Log button, Validate & Close : the track is shown on the screen ! Some touching up are sometimes necessary on particular points (under trees, closed valley, in some buildings...)
  6. If waypoints were added during the outing, use the Read Waypoints button : waypoints from the GPS and closed to the route get before will be inserted.

Importation and Exportation with GPSTrack / G7toWin

Importation

Exportation

Nov. 2001


Back to main help