Description Usage Arguments Details Examples
We want to return the reference polygons whose areal overlap with the container falls within some threshold
1 | gEnclosedArea(container, reference, threshold = 0.99)
|
container |
The single polygon that will enclose the set of reference polygons |
reference |
The set of polygons that will be selected down to the containing polygon based on areal overlap |
threshold |
The percent of areal overlap required for inclusion |
This function uses name matching / extraction. It's a kludge and often fails. use gPolyByIntersect
instead. Preserved for existing code that uses it.
Note: all inputs should be of class sp::SpatialPolygons|Points
.
Areal calculations really only work if the input polygons are rendered in the same planar projection.
1 2 3 4 5 6 7 8 9 10 | require(sp)
# Use the US National Atlas Lambert Equal Area projection
drivetime.proj = spTransform(drivetime, CRSobj = CRS(EPSG[EPSG$code == 2163 & !is.na(EPSG$code), "prj4"]))
blockgroups.proj = spTransform(block_groups, CRSobj = CRS(EPSG[EPSG$code == 2163 & !is.na(EPSG$code), "prj4"]))
# Return only the blockgroups whose overlap exceeds 20%
gEnclosedArea(drivetime.proj, block_groups.proj, threshold = 0.2)
# Often it will be faster to work with a subset of reference polygons
reference.bg.proj = gBoundingPoly(drivetime.proj, blockgroups.proj, tolerance = 1.25)
gEnclosedArea(drivetime.proj, reference.bg.proj, threshold = 0.2)
|
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