MATLAB Examples

# pathdist

The pathdist function uses the distance function to calculate cumulative distance traveled along a path given by the arrays lat and lon. (Requires Mapping Toolbox). Always assumes WGS84 ellipsoid.

## Syntax

```pathDistance = pathdist(lat,lon)
pathDistance = pathdist(...,LengthUnit)
pathDistance = pathdist(...,track)
pathDistance = pathdist(...,'refpoint',[reflat reflon])```

## Description

pathDistance = pathdist(lat,lon) returns the cumulative distance traveled along the path given by (lat,|lon|). Distance is in meters by default, referenced to the WGS84 ellipsoid. The pathDistance array will be the same size as lat and lon.

pathDistance = pathdist(...,LengthUnit) specifies any valid length unit. The following are a few LengthUnit options. See documentation for validateLengthUnit for a complete list of options.

• meter 'm', 'meter(s)', 'metre(s)' (default)
• kilometer 'km', 'kilometer(s)', 'kilometre(s)'
• nautical mile 'nm', 'naut mi', 'nautical mile(s)'
• foot 'ft', 'international ft','foot', 'international foot', 'feet', 'international feet'
• inch 'in', 'inch', 'inches'
• yard 'yd', 'yds', 'yard(s)'
• mile 'mi', 'mile(s)','international mile(s)'

pathDistance = pathdist(...,track) uses the input string track to specify either a great circle/geodesic or a rhumb line arc. If track equals 'gc' (the default value), then great circle distances are computed on a sphere and geodesic distances are computed on the WGS84 ellipsoid. If track equals 'rh', then rhumb line distances are computed on the WGS84 ellipsoid.

pathDistance = pathdist(...,'refpoint',[reflat reflon]) references the path distance to the point along the path nearest to [reflat reflon]. For this calculation, pathdist finds the point in lat and lon which is nearest to [reflat reflon] and assumes this point along lat,|lon| is the zero point. This is only an approximation, and may give erroneous results in cases of very sharply-curving, crossing, or otherwise spaghetti-like paths; where [reflat reflon] lies far from any point along the path, or where points along the path are spaced far apart.

## Example 1: Find distance traveled along a route marked by GPS measurements

This example uses the built-in sample_route.gpx route.

```route = gpxread('sample_route.gpx'); % some sample data lat = route.Latitude; lon = route.Longitude; time = 0:255; % assume GPS measurements logged every minute % Create a map of the route: figure('position',[100 50 560 800]) subplot(3,1,1) usamap([min(lat)-.05 max(lat)+.05],[min(lon)-.08 max(lon)+.08]) plotm(lat,lon,'ko-') textm(lat(1),lon(1),'start','color',[.01 .7 .1]) textm(lat(end),lon(end),'end','color','r') % Plot distance traveled: metersTraveled = pathdist(lat,lon); subplot(3,1,2) plot(time,metersTraveled) box off; axis tight; xlabel('time (minutes)') ylabel('meters traveled') % Plot speed: speed = diff(metersTraveled/1000)./diff(time/60); subplot(3,1,3) plot(time(2:end)-.5,speed) box off; axis tight xlabel('time (minutes)') ylabel('speed (km/hr)') ```

## Example 2: Calculate path length in miles referenced to a point

Adding to the plot above, we will define a reference point at (42.354 N, 71.2 W). Then we will look at travel time as a function of distance from the reference point.

```reflat = 42.354; reflon = -71.2; subplot(3,1,1) plotm(reflat,reflon,'bp') textm(reflat,reflon,'reference point','color','b') miFromRefPt = pathdist(lat,lon,'refpoint',[reflat reflon],'miles'); subplot(3,1,2) plot(miFromRefPt,time) ylabel('travel time (min)') xlabel('distance from reference point (miles)') axis tight; box off; ```

## Author Info:

This function was written by Chad A. Greene of the Institute for Geophysics at the University of Texas at Austin. June 23, 2014. Updated January 2015 to include more LengthUnit options.