Mapping Toolbox

stdist

Compute standard distance of geographic data

Syntax

dist = stdist(lat,lon) returns a row vector of the latitude and longitude geographic standard distance for the data points specified by the columns of lat and lon.

dist = stdist(lat,lon,units) indicates the angular units of the data. When the standard angle string units is omitted, 'degrees' is assumed. Output measurements are in terms of these units (as arc length distance).

dist = stdist(lat,lon,ellipsoid) specifies the elliptical definition of the Earth to be used with the two-element ellipsoid vector. The default ellipsoid model is a spherical Earth, which is sufficient for most applications. Output measurements are in terms of the distance units of the ellipsoid vector.

dist = stdist(lat,lon,ellipsoid,units,method) specifies the method of calculating the standard distance of the data. The default, 'linear', is simply the average great circle distance of the data points from the centroid. Using 'quadratic' results in the square root of the average of the squared distances, and 'cubic' results in the cube root of the average of the cubed distances.

Background

The function stdm provides independent standard deviations in latitude and longitude of data points. stdist provides a means of examining data scatter that does not separate these components. The result is a standard distance, which can be interpreted as a measure of the scatter in the great circle distance of the data points from the centroid as returned by meanm.

Description

The output distance can be thought of as the radius of a circle centered on the geographic mean position, which gives a measure of the spread of the data.

Examples

Generate latitude and longitude matrices using the worldlo data set (compare with the example for stdm):

• load worldlo
  lat=[PPpoint(2:5).lat]
  lat =
      5.3386   24.5808    5.4619   36.8862
  lon=[PPpoint(2:5).long]
  lon =
     -3.7602   54.9619   -0.3450   35.5141
  dist= stdist(lat,lon)
  dist =
     26.5282
  

See Also

meanm	Mean of geographic data
stdm	Standard deviation of geographic data

spzerom

stdm