calcCentroid function

Calculate the Centroids of Polygons

Calculate the centroids of polygons found in a PolySet .

calcCentroid (polys, rollup = 3)

Arguments

• polys: PolySet to use.
• rollup: level of detail in the results; 1 = PIDs only, 2 = outer contours only, and 3 = no roll-up. When rollup equals 1 and 2, the function appropriately adjusts for polygons with holes.

Details

If rollup equals 1, the results contain a centroid for each unique PID only. When it equals 2, they contain entries for outer contours only. Finally, setting it to 3

prevents roll-up, and they contain a centroid for each unique (PID, SID).

Returns

PolyData with columns PID, SID (may be missing), X, and Y.

Author(s)

Nicholas M. Boers, Staff Software Engineer

Jobber, Edmonton AB

Last modified Rd: 2013-04-10

See Also

calcArea, calcLength, calcMidRange, calcSummary, locateEvents, 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 and print the centroids for several polygons
  print(calcCentroid(nepacLL[is.element(nepacLL$PID,c(33,39,47)),]))
})