Calculate the Centroids of Polygons

Description

Calculate the centroids of polygons found in a PolySet.

Usage

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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).

Value

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

See Also

calcArea, calcLength, calcMidRange, calcSummary, locateEvents, locatePolys.

Examples

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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)),]))
})

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