Data Hacking

186 Part III — Data Hacking
The data at the top of the file is called the header data and contains information about the what
the file is, what created it, and where the layout of the file is stored (the TopoGrafix website).
Leave this information alone, as making changes to it can cause the file to be unreadable by
EasyGPS:
2004-11-18T15:59:12Z
The next section of the file contains information relating to the range of data held by the file.
The terms minlon and minlat stand for minimum longitude and minimum latitude, respectively,
while maxlon and maxlat stand for maximum longitude and maximum latitude, respectively.
This is used by the file to speed up the sorting of the data by latitude and longitude:
39.0589602004-11-18T15:48:31Z
BENCH
BENCH
Scenic Area
Scenic Area
Next you come to the data relating to the waypoints themselves. The data is quite straightforward
to read and edit. Latitude and longitude (lat and lon) are stored in degrees and decimal
degrees, with – used to signify southern latitudes and eastern longitudes. The + symbol is not
required for northern latitudes and western longitudes. All the coordinates used are relative to
WGS84. Time is stored in Universal Coordinated Time (UTC) format and not local time.
Name and description are text fields and symbol specifies the type of symbol used; type enables
you to enter a text description for the symbol. Symbols are device-dependant and I recommend
that you only edit these with the appropriate software. Elevation (ele) information is in meters.
You can edit these values with any text editor to whatever value that you want. For example,
let’s say that when you look at the map, you find that the elevation at the site for the coordinates
is 55 meters instead of the 39.058960 (a measurement that is accurate to a fraction of a
millimeter and totally unrealistic for a GPS), you simply change the value. While you are at it,
change the time too:
55.0000002004-11-22T12:31:00Z
BENCH
BENCH
Scenic Area
Scenic Area
Using the format laid out, you can also use the file to create new waypoints. The basic skeleton
that holds the data is as follows: