I feel a bit lazy asking for help, as I know I can do this -- but
since I don't work with spatial polygons frequently, I find
assembling objects consisting of nested polygons to be a bit
challenging.
I have a Spatial Polygons Data Frame object named "s2poly" (read in
from a polygons shapefile). The first portion of the output from
str(s2poly) is shown here:
Formal class 'SpatialPolygonsDataFrame' [package "sp"] with 5 slots
..@ data :'data.frame': 1173 obs. of 11 variables:
.. ..$ OBJECTID : num [1:1173] 3 12 13 77 78 79 80 81 82 83 ...
.. ..$ ENTITY : Factor w/ 0 levels: NA NA NA NA NA NA NA NA NA NA ...
.. ..$ HANDLE : Factor w/ 1173 levels "10002","10008",..: 348
349 350 351 352 353 354 355 356 357 ...
.. ..$ LAYER : Factor w/ 15 levels
"ADMIN_MAP","B-BLDG-LINE",..: 14 8 8 8 8 11 11 11 11 9 ...
.. ..$ COLOR : num [1:1173] 252 4 4 4 4 200 200 200 200 7 ...
.. ..$ LINETYPE : Factor w/ 3 levels "Continuous","DASHED",..: 1 1
1 1 1 1 1 1 1 1 ...
.. ..$ ELEVATION : num [1:1173] 0 0 0 0 0 0 0 0 0 0 ...
.. ..$ THICKNESS : num [1:1173] 0 0 0 0 0 0 0 0 0 0 ...
.. ..$ TEXT : Factor w/ 0 levels: NA NA NA NA NA NA NA NA NA NA ...
.. ..$ SHAPE_AREA: num [1:1173] 10.8 32549.7 16571.2 37.7 59.2 ...
.. ..$ SHAPE_LEN : num [1:1173] 19 932.6 608 77.4 120.3 ...
.. ..- attr(*, "data_types")= chr [1:11] "N" "C" "C" "C" ...
..@ polygons :List of 1173
.. ..$ :Formal class 'Polygons' [package "sp"] with 5 slots
.. .. .. ..@ Polygons :List of 1
.. .. .. .. ..$ :Formal class 'Polygon' [package "sp"] with 5 slots
.. .. .. .. .. .. ..@ labpt : num [1:2] 1653186 431813
.. .. .. .. .. .. ..@ area : num 10.8
.. .. .. .. .. .. ..@ hole : logi FALSE
.. .. .. .. .. .. ..@ ringDir: int 1
.. .. .. .. .. .. ..@ coords : num [1:8, 1:2] 1653190 1653190
1653187 1653188 1653183 ...
.. .. .. ..@ plotOrder: int 1
.. .. .. ..@ labpt : num [1:2] 1653186 431813
.. .. .. ..@ ID : chr "0"
.. .. .. ..@ area : num 10.8
I suspect, but have not confirmed, that some of the instances of
Polygons objects have length > 1.
I have also created a simple polygon named "s2bound" that surrounds
all of the polygons in s2poly.
I need a single object that I can give to spsample() in which all of
the polygons in s2poly are holes within s2bound.
I don't need to keep any of the attributed data in @data, so I
believe I can simplify to a SpatialPolygons object.
My basic request for assistance is this:
- can it be done with a modest number of high levels functions?
(and if so, I think I need to be shown how)
- or will I need to write nested loops of @Polygons within
@polygons to change @hole to TRUE in every polygon, in order
construct my final polygon?
Thanks
-Don
--
--------------------------------------
Don MacQueen
Environmental Protection Department
Lawrence Livermore National Laboratory
Livermore, CA, USA
925-423-1062
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