projecting shape files, in R?
All this information is relevant and belongs in the thread. Please stay on-list. Showing us the map would help someone help you. With the actual coordinates some one could even have a stab at guessing. This is no more doable in ArcGis than any other program - the history and clues are all that matters. Cheers, Mike On 7 Oct 2014 00:42, "Alessandra Carioli" <alessandracarioli at gmail.com> wrote:
Thanks for your answers. Mine was a general question with a more particular need behind, more into detail I am dealing with a map of Spain with ?custom made? polygons, where I have 910 centroids with some coordinates in a unit that should be meters. I say should be because it looks like meters, I?ve calculated distances between cities and it makes sense, but I have no absolute proof (no ?read me? note with ?distances are in meters"). My centroids are cities and I know all of them. Of course if I googled the name of each and every city I would know the exact latitude and longitude, but I want to have that information in a prj file (plus googling 910 times and creating long-lat vectors is time consuming) so that my map would be in a mercator style, while right now is in a I know this can be done in Arcgis but I'd like to be R-sufficient. If I had the .prj file this would not be an issue, but I don?t. Message: 1 Date: Fri, 3 Oct 2014 13:32:39 +0200 From: Alessandra Carioli <alessandracarioli at gmail.com> To: r-sig-geo at r-project.org Subject: [R-sig-Geo] projecting shape files, in R? Message-ID: <0A114832-F81A-4B1D-8B9C-8F26DBF3C686 at gmail.com> Content-Type: text/plain; charset=windows-1252 Dear Mailing list members, I need a projected shape file but I don?t have the .prj information and I was wondering if anything like projecting a shape file to obtain coordinates in longitude and latitude can be done. My issue is that I am producing semivariograms and, although I think distances are in meters, I want to be 100% sure. Also, being the considered area rather big (Europe) considering the projected coordinated would make my computation more precise. Any ideas? Ale ------------------------------ Message: 2 Date: Fri, 3 Oct 2014 13:54:16 +0200 From: Janka Vanschoenwinkel <janka.vanschoenwinkel at uhasselt.be> To: Alessandra Carioli <alessandracarioli at gmail.com> Cc: "r-sig-geo at r-project.org" <r-sig-geo at r-project.org> Subject: Re: [R-sig-Geo] projecting shape files, in R? Message-ID: <CAHymutJEhjpZZyh_vMCF12LdqPwv9VXgMtyBj-wzSPREn-kV8w at mail.gmail.com> Content-Type: text/plain; charset="UTF-8" Dear Alessandra, I am still relatively new in using R, but I can make my .prj files myself. By using the following command, I can make a shapefile with the information I already uploaded. It gives me the .dbf, .prj, .shp and .shx files. writeOGR(data, dsn = ".", layer ='choose name', driver = 'ESRI Shapefile') You didn't give a lot of information so I don't know exactly if this line is also applicable to your case. I think it depends on your data, but maybe somebody more experienced can give additional or other advice. Or you can look up the code line I wrote in the help box! Good luck! Janka 2014-10-03 13:32 GMT+02:00 Alessandra Carioli <alessandracarioli at gmail.com
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Dear Mailing list members, I need a projected shape file but I don?t have the .prj information and I was wondering if anything like projecting a shape file to obtain coordinates in longitude and latitude can be done. My issue is that I am producing semivariograms and, although I think distances are in meters, I want to be 100% sure. Also, being the considered area rather big (Europe) considering the projected coordinated would make my computation more precise. Any ideas? Ale
_______________________________________________ R-sig-Geo mailing list R-sig-Geo at r-project.org https://stat.ethz.ch/mailman/listinfo/r-sig-geo [[alternative HTML version deleted]] ------------------------------ Message: 3 Date: Fri, 3 Oct 2014 22:09:49 +1000 From: Michael Sumner <mdsumner at gmail.com> To: Alessandra Carioli <alessandracarioli at gmail.com> Cc: RsigGeo <r-sig-geo at r-project.org> Subject: Re: [R-sig-Geo] projecting shape files, in R? Message-ID: <CAAcGz9-8AfMyCat3Z6XkYB0kz+-kx3iaWFa8mCdokqC6RbLu+w at mail.gmail.com> Content-Type: text/plain; charset=UTF-8 It's not really possible to guess from a literally infinite number of possible projections. Usually there is some information, or you can infer it from context. Really you need at least the family of the projection, then you can maybe guess at the details until you find a good match. Experience can provide the family by looking at the data, but only careful hunting can find the details. It's important to find and tell the story of what the data are, clues are hidden in many ways. For example, this map was fairly simple to work out (for me, given my background, the people I know, the stuff I've seen 'around here'): http://www.bom.gov.au/ant/seaice/ Through experience I know that 71 S is a commonly used latitude for the "true scale" of a Polar Stereographic projection, and that Polar Stereographic (the family) is pretty popular for Antarctic data. (It's because the coast of Antarctica is roughly "averagely" at 70S, and secant-slicing the ellipsoid at this latitude provides a better fit for areas around the coast, a good compromise compared to the single tangent at the south pole). But, perspective on this aspect of PS is relatively new for me. The rest was easy, I can find two points with the printed graticule, and also determine the central longitude at 110E and so with tools to transform longlat to PS I can fully georeference this image - well good enough that I cannot see a problem. I cannot see any of this metadata on the web page, so I had to resort to personal experience and socio-historical heuristics. (I'm still not sure if this uses WGS84, a sphere, or maybe Hughes 1980 - I have to do some more tests to be sure, but maybe it's not answerable or maybe doesn't even matter). So, you need to go hunting in your own social context, show us the map, give us more clues. It's possible to guess/get lucky, but you really need to find out all the details. Guessing from nothing is a no-hope. There are some CRS that won't be candidates given the range though, for example it's unlikely that for all of Europe that UTM is used so you need some idea about the sensible scope for different families - clues in one direction - as well as knowledge about the data, what it's used for, and so on - from the other direction. Cheers, Mike.