calcLength: Calculate the Length of Polylines

In PBSmapping: Mapping Fisheries Data and Spatial Analysis Tools

Description

Calculate 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.

Author(s)

Nicholas M. Boers, Associate Professor – Computer Science
MacEwan University, Edmonton AB
Last modified Rd: 2013-04-10

See Also

calcArea, calcCentroid, calcMidRange, calcSummary, locatePolys.

Examples

local(envir=.PBSmapEnv,expr={
  #--- load the data (if using R)
  if (!is.null(version$language) && (version$language=="R"))
    data(nepacLL,envir=.PBSmapEnv)
  #--- calculate the perimeter of Vancouver Island
  print(calcLength(nepacLL[nepacLL$PID==33, ]))
})

Example output

sh: 1: cannot create /dev/null: Permission denied

-----------------------------------------------------------
PBS Mapping 2.70.4 -- Copyright (C) 2003-2018 Fisheries and Oceans Canada

PBS Mapping comes with ABSOLUTELY NO WARRANTY;
for details see the file COPYING.
This is free software, and you are welcome to redistribute
it under certain conditions, as outlined in the above file.

A complete user guide 'PBSmapping-UG.pdf' is located at 
/usr/lib/R/site-library/PBSmapping/doc/PBSmapping-UG.pdf

Packaged on 2017-06-28
Pacific Biological Station, Nanaimo

All available PBS packages can be found at
https://github.com/pbs-software

To see demos, type '.PBSfigs()'.
-----------------------------------------------------------


  PID   length
1  33 2866.661

PBSmapping documentation built on Jan. 15, 2021, 3:41 p.m.