![]() | ![]() | ![]() | Tracks |
A track has a datum for all its points, a colour and a width (in pixels) used in displaying it on the map. The colour will be sent to the GPS receivers supporting it, in which process a colour matching algorithm will be applied if the original colour is not in the set of colours accepted by the receiver. Any colour matching algorithm may give unexpected results and the one used in GPSMan is no exception.
A map background image name can be given for each track, so that when the track is displayed on the map window the named image is automatically loaded if the map is empty. See below for the details.
Each track point has the following information: time stamp, position (always shown in the DMS format), altitude and depth in either metres or feet, depending on the existing option for this.
A track can be subdivided into segments by some receivers at points in which the GPS fix was lost. The first track point always starts a segment, and any other track point can be marked as a segment starter from the track edit window by using the mouse right-button on the last column of the points list. When displaying a track with segments on the map, the segments will not be connected.
The edit window for tracks allows some operations on tracks that may be useful to clean uninteresting start or end parts of a track, or to compose a single track from several others. They are:
The computation results are the following
An elevation graph for a track
can be plotted, as a side-view or a perspective, from the
track computation window if there are at least
3 track points with a valid altitude field. They are similar
to the elevation graphs for routes,
although the side-view graph can be plotted against time
instead of total distance if there is valid time
information. Another difference is that gaps
between segments are shown as interrupted lines.
A speed graph for a track
can be plotted from the track computation window if there are at least
3 track points with valid time information. It is similar to the
side-view elevation graph and can also be plotted against time instead
of total distance, but does not answer to A climb rate graph for a track
can be plotted from the track computation window if there are at least
3 track points with valid time information. The graph is plotted
against time, the vertical units being (user selected) altitude unit
per second. If there is enough points a noise-reducing filter, kindly
provided by Paul Scorer, is applied to the data.
Creating a waypoint from a track point
can be done by double clicking with the mouse left-button on a
track point listed in a track window. This will open, for edition, a
new waypoint having the same coordinates unless there is already a
waypoint being edited. If the track is currently on the map the
number of each
track point together with
the track name will appear in the help balloon when the cursor is
over the point.
A waypoint with average coordinates
can be created from a
track window. Its latitude, longitude and altitude will be computed
as the averages of the latitudes, longitudes and altitudes of the
track points. This will be useful for obtaining more precise
coordinates for a
waypoint by recording a
track with the receiver standing still.
A track can be splitted
by taking either each selected track point or segment starter as the
first point of a new track extending up to and excluding the next such
point. Tracks with at least two points obtained in this way are
created, as well as a group with all of them. These new tracks inherit
the datum, segments (unless when splitting by segment starters),
width, colour and map background of the original track but hidden
information is discarded. They and the new group get names generated
automatically. The original track is not affected by this
operation.
A track can be converted into other sorts of line items
by a simplifying algorithm that keeps a certain number of the track
points as points of the new line, which can be a route, another track,
or a polyline. When converting to a polyline information on
segments is only used if all the points are kept.
The algorithm that was developed for this may be seen as a variant of
the Douglas-Peucker algorithm for finding critical points in polylines
(see, e.g., [Heckbert and Garland, 1997] or [Li,
1995]). It starts from a straight line between the first and
the last track points; if the number of points to keep is greater than
2, any point that stands furthest from the line will be retained, and
the line is replaced by two new lines, those from the first to the new
point and from it to the last one. This procedure is repeated always
replacing one of the lines for which the distance to an intermediate
point is maximum. The review of [Heckbert and Garland,
1997] describes an algorithm by Ballard and Brown (published
in 1982) that seems to be very close to this one.
The sequence available here shows examples of
routes with 3, 6, 11, 15 and 31 waypoints obtained from a track having
739 track points.
Although GPSMan lets the user fix the number of points to keep
between 2 and the number of track points, there is a maximum number of
points per route depending on the GPS receiver. It should also be
noted that the time needed to find the simplified line will increase
significantly with the number of points (although keeping all the
track points will take only the time to create the new item).
So that a choice may be made between different numbers of points, GPSMan
may be asked to display the simplified line and also the original
track on the map on the fly. When the user clicks the An animation
of the movement corresponding to a track can be viewed in the map
window ( A track can be created from a route or a polyline
from the route window or the polyline window.
Control
key
plus mouse left-button.
Ok
button, the map will be
restored, the simplified line is used in forming a new item (in the
case of a route, with new waypoints having names of the form
ZT
n, with n a 4-digit integer), and an edit window will be
opened for editing the new item. If the edit window for the item type
was already in use, then the item is created under an
automatically generated name. For a route GPSMan will create a
new group with all
the new waypoints for easier access.
Animation
button in the track edit/show window). A
control window will appear that allows for (re-)starting, pausing, or
aborting the animation, for skipping to the next track point, for
setting the speed (the scale changes are exponential), and for
choosing whether the last point shown will be centred on the map
window. The default speed is that in the track: the delay between the
presentation of two consecutive points is the difference between their
time stamps. If a time stamp is not defined the default delay is 30
seconds. The state of the animation, the total (real) time since
the beginning (if defined), the time stamp (if defined) and
total distance along the track are displayed.
GPSMan User Manual
©1998-2009 Miguel
Filgueiras,
mig_at_ncc.up.pt
, LIACC & DCC Faculdade de Ciências, Universidade do Porto
Tracks