calcLength {PBSmapping}R Documentation

Calculate the Length of Polylines

Description

Calculates the length of polylines found in a PolySet.

Usage

calcLength (polys, rollup = 3, close = FALSE)

Arguments

polys PolySet to use.
rollup level of detail in the results; 1 = PIDs only, summing the lengths of each SID within each PID, and 3 = no roll-up. Note: rollup 2 has no meaning in this function and, if specified, will be reset to 3.
close Boolean value; if TRUE, include the distance between each polygon's last and first vertex, if necessary.

Details

If rollup equals 1, the results contain an entry for each unique PID only. Setting it to 3 prevents roll-up, and they contain an entry for each unique (PID, SID).

If the projection attribute equals "LL", this routine uses Great Circle distances to compute the surface length of each polyline. In doing so, the algorithm simplifies Earth to a sphere.

If the projection attribute equals "UTM" or 1, this routine uses Pythagoras' Theorem to calculate lengths.

Value

PolyData with columns PID, SID (may be missing), and length. If projection equals "UTM" or "LL", lengths are in kilometres. Otherwise, lengths are in the same unit as the input PolySet.

See Also

calcArea, calcCentroid, calcMidRange, calcSummary, locatePolys.

Examples

#--- load the data (if using R)
if (!is.null(version$language) && (version$language == "R"))
  data(nepacLL)
#--- calculate the perimeter of Vancouver Island
print(calcLength(nepacLL[nepacLL$PID == 33, ]))
[Package PBSmapping version 2.09 Index]