trkvu.icn: Program to display GPS track logs

Trkvu displays GPS track logs, using color to indicate various
characteristics such as velocity, direction, or time of day.
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usage:  trkvu file...

Each file argument is a track log uploaded from a GPS receiver.
Lines that end in three decimal values specify latitude, longutude,
and altitude in that order.  Lines with just two values omit the
altitude.  Lines without data indicate breaks between segments.

Some colorings use timestamps from the track logs.  A timestamp
has the form "mm/dd/yyyy hh:mm:ss" or "yyyy/mm/dd hh:mm:ss" and
precedes the latitude and longitude.
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Track log colorings are selected by pressing a key:

F       color by File (restricting legend to files in view)
A       color by Age
O       color by Orientation (direction of travel)
V       color by Velocity
I       color by Interval duration (GPS sample rate)
S       color Segments in contrasting colors
Y       color by time of Year
D       color by Day of week
H       color by Hour of day
M       color by Minute (repeating colors every 10 minutes)
T       color by Time of day

Colorings can also be cycled:

SP or CR        cycle to next coloring
BS or DEL       cycle to preceding coloring

A legend explains each coloring.  If it shows individually labeled
color blocks, the colors encode discrete values.  If a spectrum
is shown, the colors vary smoothly over a continuous range.

Some colorings require timestamps.  For these, tracks lacking
timestamps are drawn in gray.
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Zooming and Panning:

To zoom to a particular region, sweep out the region using the
left mouse button.  To cancel a sweep, reduce its width or height
to fewer than ten pixels.

The window may be resized as desired.

The following keyboard commands also affect the display region:

+ or =          zoom in
- or _          zoom out
0 or Home       zoom to initial view
arrow keys      pan the display  (hold Shift key for smaller pan)