[R-sig-Geo] how to create several polygons from a list of vertices

[Antonio Silva]

Thanks Lulla,

Nice solution. I could also export it as a shapefile after transforming it
to a spatial polygon dataframe.

The problem is that I could not "individualize" the squares in a multipart
layer. They all have the same ID. I tried to change this without success:
"Single ID required".

The attribute table of the shapefile should have 6 lines in my example and
not only one.

Any other option?

Thanks again,

Antonio Olinto


Em ter, 14 de ago de 2018 às 18:10, Vijay Lulla <vijaylulla using gmail.com>
escreveu:

> Maybe something like this?
>
> poly <- SpatialPolygons(list(Polygons(tapply(seq_len(nrow(vertices)),
>                                              vertices$cod,
>                                              function(x)
> Polygon(vertices[x,1:2])), ID="1")),
>                         proj4string=CRS("+proj=longlat +ellps=WGS84
> +datum=WGS84 +no_defs"))
>
>
> On Tue, Aug 14, 2018 at 4:17 PM Antonio Silva <aolinto.lst using gmail.com>
> wrote:
>
>> Hi,
>>
>> I have a data.frame with the vertices (lon / lat) and codes from several
>> squares (more than 500 in the real dataset).
>> I want to create an object with these polygons (squares) and after this
>> export it as a shapefile.
>> With the script below I can draw one square.
>> library(sp)
>> P1 = Polygon(vertices[1:4,1:2])
>> Ps1 = SpatialPolygons(list(Polygons(list(P1), ID = "1")),
>> proj4string=CRS("+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs"))
>> plot(Ps1, axes = TRUE)
>>
>> Now I'm trying to create one object with all squares at once.
>> Is it possible?
>>
>> Thanks a lot,
>>
>> Antônio Olinto
>>
>> sample data:vertices
>>    lon lat cod
>> 1  -33 -23   1
>> 2  -32 -23   1
>> 3  -32 -22   1
>> 4  -33 -22   1
>> 5  -32 -23   2
>> 6  -31 -23   2
>> 7  -31 -22   2
>> 8  -32 -22   2
>> 9  -31 -23   3
>> 10 -30 -23   3
>> 11 -30 -22   3
>> 12 -31 -22   3
>> 13 -33 -22   4
>> 14 -32 -22   4
>> 15 -32 -21   4
>> 16 -33 -21   4
>> 17 -32 -22   5
>> 18 -31 -22   5
>> 19 -31 -21   5
>> 20 -32 -21   5
>> 21 -31 -22   6
>> 22 -30 -22   6
>> 23 -30 -21   6
>> 24 -31 -21   6
>>
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>>
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