Automatic Map Scale Generation

Intelligently creates and places a scale on a figure based on the lat/lon limits.

MAKESCALE creates a scale for map data.

MAKESCALE creates a scale on the current axis based on the current axis
limits. The scale is made to occupy 1/5th of the map. It is placed
in the southeast corner of the map. The units will either be in
milimeters, meters or kilometers, depending on the size of the map.

MAKESCALE(H_AXIS) creates a scale on the axis specificed by the handle
H_AXIS based on the its axes limits. H_AXIS must be a scalar.

MAKESCALE(SCALE) creates a scale made to occupy 1/SCALE of the map.
SCALE must be a scalar, and is bounded to be between 1.1 and 10. If
a larger value is passed in, 10 will be used. If a smaller value is
passed in, 1.1 will be used.

MAKESCALE(LOCATION) places the scale in the location specified by
LOCATION. Acceptable values for location are as follows
'northeast' 'ne'
'northwest' 'nw'
'southeast' 'se'
'southwest' 'sw'
'north' 'n'
'south' 's'

MAKESCALE('units',UNITS) changes the units systems from SI to imperical
units. UNITS should be either 'si' or 'imp.' The units displayed
are automatically switched between milimeters, meters, and
kilometers for the SI system, or between inches, feet, and statuate
miles for the imperical system.

H = MAKESCALE(...) outputs H, a 3x1 containing the handles of the of
box, line, and text.

Any number of these input sets may be passed in any order.

The map scale will automatically be updated as the figure is zoomed,
panned, resized, or clicked on. It will not, however, be updated
upon using the commands "axis", "xlim", or "ylim" as these do not
have callback functionality.

Example:
load conus
figure
plot(uslon,uslat);
makeScale

Example: Placed in the south
load conus
figure
plot(uslon,uslat);
makeScale('south')

Example: Half the size of the Window
load conus
figure
plot(uslon,uslat);
makeScale(2,'south')

Example: Use Imperical Units
load conus
figure
plot(uslon,uslat);
makeScale(2,'south','units','imp')

Example: Zooming In
load conus
figure
plot(uslon,uslat);
makeScale(2,'south')
zoom(2)

Note: This assumes axis limits are in degrees. The scale is sized
correctly for the center latitude of the map. As the size of
degrees longitude change with latitude, the scale becomes invalid
with very large maps. Spherical Earth is assumed. Ideally, the map
will be proportioned correctly in order to reflect the relationship
between a degree latitude and a degree longitude at the center of
the map.

By Jonathan Sullian - October 2011