[R-sig-Geo] Convert SpatialPointsDataFrame to SpatialPolygons or SpatialPolygonsDataFrame

[Miluji Sb]

Dear Michael,

Merry Christmas and seasons's greetings! Thank you for your reply, I am
providing more information and my attempts to convert
to SpatialPolygonsDataFrame below.

The original SpatialPointsDataFrame has the following attributes:

class       : SpatialPointsDataFrame
features    : 21441
extent      : -179.5, 179.5, -89.5, 83.5  (xmin, xmax, ymin, ymax)
coord. ref. : +proj=longlat +ellps=WGS84
variables   : 3
names       : ID_cell,    lon,   lat
min values  :    2304, -179.5, -89.5
max values  :   64800,  179.5,  83.5

The data looks like this:

dput(head(shp at data,20))
structure(list(ID_cell = c(2304L, 2305L, 2306L, 2307L, 2308L,
2309L, 2310L, 2311L, 2618L, 2619L, 2620L, 2621L, 2622L, 2623L,
2624L, 2625L, 2626L, 2627L, 2628L, 2629L), lon = c(-36.5, -35.5,
-34.5, -33.5, -32.5, -31.5, -30.5, -29.5, -82.5, -81.5, -80.5,
-79.5, -78.5, -77.5, -76.5, -75.5, -74.5, -73.5, -72.5, -71.5
), lat = c(83.5, 83.5, 83.5, 83.5, 83.5, 83.5, 83.5, 83.5, 82.5,
82.5, 82.5, 82.5, 82.5, 82.5, 82.5, 82.5, 82.5, 82.5, 82.5, 82.5
)), .Names = c("ID_cell", "lon", "lat"), data_types = c("N",
"F", "F", "C", "C", "C", "C"), row.names = c("0", "1", "2", "3",
"4", "5", "6", "7", "8", "9", "10", "11", "12", "13", "14", "15",
"16", "17", "18", "19"), class = "data.frame")

I tried the following:

x = as(SpatialPixelsDataFrame(shp, shp at data, tolerance=.00086),
"SpatialPolygonsDataFrame"), it seemed to have worked but got the following
warning:

Warning message:
In points2grid(points, tolerance, round) :
  grid has empty column/rows in dimension 2

Now the converted SpatialPolygonsDataFrame has the following attributes:

class       : SpatialPolygonsDataFrame
features    : 21441
extent      : -180, 180, -90, 84  (xmin, xmax, ymin, ymax)
coord. ref. : +proj=longlat +ellps=WGS84
variables   : 3
names       : ID_cell,    lon,   lat
min values  :    2304, -179.5, -89.5
max values  :   64800,  179.5,  83.5

structure(list(ID_cell = c(2304L, 2305L, 2306L, 2307L, 2308L,
2309L, 2310L, 2311L, 2618L, 2619L, 2620L, 2621L, 2622L, 2623L,
2624L, 2625L, 2626L, 2627L, 2628L, 2629L), lon = c(-36.5, -35.5,
-34.5, -33.5, -32.5, -31.5, -30.5, -29.5, -82.5, -81.5, -80.5,
-79.5, -78.5, -77.5, -76.5, -75.5, -74.5, -73.5, -72.5, -71.5
), lat = c(83.5, 83.5, 83.5, 83.5, 83.5, 83.5, 83.5, 83.5, 82.5,
82.5, 82.5, 82.5, 82.5, 82.5, 82.5, 82.5, 82.5, 82.5, 82.5, 82.5
)), .Names = c("ID_cell", "lon", "lat"), data_types = c("N",
"F", "F", "C", "C", "C", "C"), row.names = c("g144", "g145",
"g146", "g147", "g148", "g149", "g150", "g151", "g458", "g459",
"g460", "g461", "g462", "g463", "g464", "g465", "g466", "g467",
"g468", "g469"), class = "data.frame")

Is this correct or even on the right track? I hope I have provided enough
information. Thank you so much.

SIncerely,

Milu

On Mon, Dec 26, 2016 at 7:24 AM, Michael Sumner <mdsumner at gmail.com> wrote:

> It is but you will need at least a grouping ID for each polygon ring
> within each object, and an order within each ring. Is ID_cell the object ID?
>
> If there is only a single ring polygon within each object and the order is
> native it's simplest, but the constructors require very particular
> arrangements of your data, there is no abstractions for this. See
> raster::spPolygons and spbabel::sp for alternative constructors, but other
> wise see Polygon, Polygons, SpatialPolygons and SpatialPolygonsDataFrame in
> sp.
>
> There's not enough information in your post to be sure of what you have,
> but I'm happy to help if you provide more detail about how your data is
> organized. You could post sample data, or describe them in more detail. Do
> you have actual  polygons here or are you attempting to estimate them from
> point data?
>
> To add more alternatives the new sf package simplifies the constructors a
> lot, for a new family of classes, but still you need to nest matrices of
> coordinates manually to use them rather than specify their organization
> abstractly.  I'm working on tools to do that, but there is only spbabel so
> far (it's really just a two-level grouping of coordinates for spatial
> objects and their parts, but various legacies make it ever more
> complicated).
>
> Cheers, Mike
>
> On Sun, Dec 25, 2016, 02:28 Miluji Sb <milujisb at gmail.com> wrote:
>
> I have a SpatialPointsDataFrame with the following attributes. Is it
> possible to convert this to a SpatialPolygons or SpatialPolygonsDataFrame?
> Thank you!
>
> Sincerely,
>
> Milu
>
> class       : SpatialPointsDataFrame
> features    : 21441
> extent      : -179.5, 179.5, -89.5, 83.5  (xmin, xmax, ymin, ymax)
> coord. ref. : +proj=longlat +a=6367470 +b=6367470 +no_defs
> variables   : 7
> names       : ID_cell,    lon,   lat, Field4, Field5, Field6, Field7
> min values  :    2304,    0.5,   0.5,     NA,     NA,     NA,     NA
> max values  :   64800, -179.5, -89.5,     NA,     NA,     NA,     NA
>
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>
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>
> --
> Dr. Michael Sumner
> Software and Database Engineer
> Australian Antarctic Division
> 203 Channel Highway
> Kingston Tasmania 7050 Australia
>
>

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