[R-sig-Geo] reading KML files in R

[Alex Mandel]

Actually I believe for kml you must use geographic coordinates
unprojected. WGS 84 Lat/Lon , EPSG:4326

And yes it's only so Google maps/earth knows what to do with it.
If I could make head or tails of OGC specs I'm sure it says something
about it in there.

Alex

On 05/29/2010 12:21 AM, Agustin Lobo wrote:
> Excuses for the quite adjacent question, does anybody know if kml files require
> using the google spherical projection?
> My understanding is that, in theory, you can use any projection, but,
> in fact, you must use
> google spherical to get a correct display in google maps
> 
> Agus
> 
> 2010/5/28 Wade Wall <wade.wall at gmail.com>:
>> Thanks Dr. Bivand,
>>
>> I was able to import my kml file using your example.  I opened up the
>> kml file in a text editor to find out the layer name, but
>> system(paste("ogrinfo", paste(td, "cities.kml", sep="/")),
>> intern=TRUE) also works to find the name.
>>
>> As for modifying ogrinfo(), I will take a look and see if it is above
>> my skill level or not.
>>
>> Wade
>>
>> On Fri, May 28, 2010 at 3:29 AM, Roger Bivand <Roger.Bivand at nhh.no> wrote:
>>> On Thu, 27 May 2010, Wade Wall wrote:
>>>
>>>> I am not exactly sure what you mean by identify the correct layer
>>>> name.  Using R under Linux, this is what happens.
>>>>
>>>> I have a file in the current directory named ASMI_GA.kml
>>>>
>>>> library(rgdal)
>>>> tmp<-readOGR(".", layer="ASMI_GA.kml")
>>>>
>>>> However, I get the following message.
>>>>
>>>> Error in ogrInfo(dsn = dsn, layer = layer, input_field_name_encoding =
>>>> input_field_name_encoding) :
>>>>  Cannot open file
>>>
>>> That is what I said. Each driver has its own understanding of what the dsn=
>>> and layer= arguments are, and your usage doesn't match what the driver is
>>> expecting. The dsn= for the KML driver seems to be the file name (possibly
>>> with its complete path), and the layer= is the string in the:
>>>
>>> <Document><Folder><name>cities</name>
>>>
>>> line (conditional on the writing software using a similar logic to OGR),
>>> here in this example:
>>>
>>> library(rgdal)
>>> cities <- readOGR(system.file("vectors", package = "rgdal")[1], "cities")
>>> is.na(cities$POPULATION) <- cities$POPULATION == -99
>>> summary(cities$POPULATION)
>>> td <- tempdir()
>>> writeOGR(cities, paste(td, "cities.kml", sep="/"), "cities", driver="KML")
>>> xx <- readOGR(paste(td, "cities.kml", sep="/"), "cities")
>>>
>>> How one discovers this name is not obvious, since the KML driver in OGR
>>> needs it to access the file. One possibility is:
>>>
>>> system(paste("ogrinfo", paste(td, "cities.kml", sep="/")), intern=TRUE)
>>>
>>> which lists the layer name(s). Perhaps ogrInfo() could be revised to access
>>> the dsn in the same way when not given a layer= argument to discover layer
>>> names - anyone with lots of time on their hands like to help?
>>>
>>> Roger
>>>
>>> PS. ogrDrivers() lists the drivers seen by OGR as running in rgdal, but for
>>> drivers with write but not read capability, it cannot distinguish. In that
>>> case, you only find out if a read driver is present and has its external
>>> dependencies properly satisfied by using it, I'm afraid. The example above
>>> will show whether your rgdal/GDAL/Expat do work or not.
>>>
>>>>
>>>> I have expat XML parser installed and gdal.  This probably sounds
>>>> rather stupid, but I am not sure what the following means in the link
>>>> that Dr. Bivand provided: "KML reading is only available if GDAL/OGR
>>>> is built with the Expat XML Parser, otherwise only KML writing will be
>>>> supported."  I installed both as debian packages (using get-apt).
>>>> Should I install both from source code, Expat XML Parser first and
>>>> then GDAL?
>>>>
>>>> Sorry if I seem dense here, but it is not real clear to me.  Also,
>>>> even though this may be beyond the scope of R-sig-geo, I think that
>>>> other people are also struggling with this.
>>>>
>>>> Thanks for any help.
>>>>
>>>> Wade
>>>>
>>>>
>>>> On Thu, May 27, 2010 at 2:15 PM, Roger Bivand <Roger.Bivand at nhh.no> wrote:
>>>>>
>>>>> On Thu, 27 May 2010, rick reeves wrote:
>>>>>
>>>>>> I do note that the example I provided does not demonstrate how to READ a
>>>>>> KML
>>>>>> file into R. But, SOON, I plan to modify the example to demonstrate
>>>>>> reading of KMLs
>>>>>> into some R-compatible format.
>>>>>
>>>>> readOGR() does read KML files, but you do have to identify the correct
>>>>> layer
>>>>> name - see:
>>>>>
>>>>> http://www.gdal.org/ogr/drv_kml.html
>>>>>
>>>>> Roger
>>>>>
>>>>>>
>>>>>> RR
>>>>>>
>>>>>> On 5/27/2010 10:15 AM, Wade Wall wrote:
>>>>>>>
>>>>>>> Hi all,
>>>>>>>
>>>>>>> Does anyone have experience reading and writing KML files in R?  I
>>>>>>> have seen several threads that seem to suggest that it is difficult if
>>>>>>> not impossible, but it is convenient to use KML files when working
>>>>>>> with Google Earth and inconvenient to read and write shapefiles and
>>>>>>> then convert to KML using other software.
>>>>>>>
>>>>>>> If anyone is able to read and write KML files, if they could provide a
>>>>>>> description of how to do it, I am sure a lot of people would
>>>>>>> appreciate it.  I have tried to do so under both Windows and Linux to
>>>>>>> no avail.  The Windows approach looks more difficult, judging by the
>>>>>>> readme file associated with rgdal.
>>>>>>>
>>>>>>> Thanks,
>>>>>>>
>>>>>>> Wade
>>>>>>>
>>>>>>> _______________________________________________
>>>>>>> R-sig-Geo mailing list
>>>>>>> R-sig-Geo at stat.math.ethz.ch
>>>>>>> https://stat.ethz.ch/mailman/listinfo/r-sig-geo
>>>>>>>
>>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>
>>>>> --
>>>>> Roger Bivand
>>>>> Economic Geography Section, Department of Economics, Norwegian School of
>>>>> Economics and Business Administration, Helleveien 30, N-5045 Bergen,
>>>>> Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
>>>>> e-mail: Roger.Bivand at nhh.no
>>>>>
>>>>>
>>>>
>>>
>>> --
>>> Roger Bivand
>>> Economic Geography Section, Department of Economics, Norwegian School of
>>> Economics and Business Administration, Helleveien 30, N-5045 Bergen,
>>> Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
>>> e-mail: Roger.Bivand at nhh.no
>>>
>>
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