Mapping Toolbox

Distance Notation

Distances in the Mapping Toolbox can be measured in a number of different units. Functions are provided to convert between nautical miles (nm), statute miles (sm), feet (ft), kilometers (km), meters (m), degrees of arc length (deg), and radians of arc length (rad). The names of these functions are of the form sm2km, km2rad, etc. A general distance conversion function, distdim, is available as well.

There is no single default unit of distance measurement in the toolbox. Navigation functions use nautical miles as a default, almanac functions default to kilometers, and the distance function defaults to degrees of arc length. It is essential that you understand the default units of any function you use.

Note    When distances are given in terms of angular units (degrees or radians), be careful to remember that these are in terms of arc length. While a degree of latitude always subtends a degree of arc length, this is not necessarily the case for degrees of longitude. Also, using arc length as distance assumes a knowledge of the underlying radius.

On the Earth, a degree of arc length is about 60 nautical miles:

• nauticalmiles = deg2nm(1)
  nauticalmiles =
      60.0405
  

The Earth is the default assumption for these conversion functions. Other radii may be used, however:

• nauticalmiles = deg2nm(1,almanac('moon','radius'))
  nauticalmiles =
      30.3338
  

Time Notation

Working with Vector Maps