[R-sig-Geo] Get coordinates from huge shapefiles.

[Michael Sumner]

Sorry, that should have been "x at y" for the raw access to S4 elements.

On Thu, Mar 1, 2012 at 7:44 AM, Michael Sumner <mdsumner at gmail.com> wrote:
> You can do this:
>
> https://stat.ethz.ch/pipermail/r-sig-geo/2010-February/007619.html
>
> (The email archive, or my browser has auto-converted "x @ y" symbols
> to "x at y" rather helpfully so you will need to fix that if that's
> what you see).
>
> The fortify tools (in ggplot2) and the geometry/topology-sense in
> rgeos are important to consider though, fortify is trying to build a
> table that still stores all the topology so that (for e.g.) ggplot2
> can work with it in a standard way.
>
> Raw extraction does not take any care with whether the polygons make
> sense, but that takes work since shapefiles just don't store that
> information, they are just sets of ring boundaries and it's up to the
> software using them to build the actual topology. My code at that post
> just drops the final duplicated coordinate . . .
>
> Cheers, Mike.
>
> On Thu, Mar 1, 2012 at 5:15 AM, Christian Jansson <chrjan70 at gmail.com> wrote:
>> Hi,
>>
>> Thanks to everyone on this list. It is a true source of help!
>>
>> I'm reading huge shapefiles like this:
>>
>> shp_0 <- rgdal::readOGR(dsn="dir", layer="TheLayer")
>>
>> There are two columns in the shp_0 at data: bin1 and bin2.
>>
>> I need to get a table with three columns: id, X, Y.
>>
>> First I do this:
>> shp_0 at data$id = rownames(shp_0 at data)
>>
>> When I then run this:
>> tbl_coords <-fortify.SpatialPolygonsDataFrame(shp_0)
>> I get: "Using bin1 to define regions.
>> Error in createPolygonsComment(p) :
>>  rgeos_PolyCreateComment: orphaned hole, cannot find containing polygon
>> for hole at index 3"
>>
>> After reading in previous messages on this email-list, I tried:
>>
>> slot(shp_0, "polygons") <- lapply(slot(shp_0, "polygons"),
>> checkPolygonsHoles), which proceeds to a new R-prompt with no issue
>> mentioned.
>>
>> But everytime I then run
>> shp_1 <- unionSpatialPolygons(shp_0, as.character(shp_0$id))
>> I get another crasch:
>> "This application has requested the Runtime to terminate it in an unusual
>> way.
>> Please contact the application's support team for more information."
>>
>> How can I get the coordinates per polygon in one large table? I know how to
>> get them per polygon, but to rbind more than 30 000 polygons take forever.
>> To get the areas is easy "sapply(shp_0 at polygons, function(x) x at area)", but
>> the coords are deeper into the sp-object and I don't know how to "apply-it
>> out".
>>
>> Thank you very much for all help.
>>
>> /Chris
>>
>>        [[alternative HTML version deleted]]
>>
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>
>
>
> --
> Michael Sumner
> Institute for Marine and Antarctic Studies, University of Tasmania
> Hobart, Australia
> e-mail: mdsumner at gmail.com



-- 
Michael Sumner
Institute for Marine and Antarctic Studies, University of Tasmania
Hobart, Australia
e-mail: mdsumner at gmail.com