[R-sig-Geo] proj4string read by readOGR doesn't seem to precisely specify source shapefile projection

Wed Jun 14 22:52:41 CEST 2017

Hi Shaun,

Yes, this would be an option, as would be avoiding shapefiles. Could you 
(or Glenn) check that the same problem exists with a GPKG written by 
ArcGIS and read into R using rgdal::readOGR() and sf::st_read(), and then 
written out again using rgdal::writeOGR() and sf::st_write? A recent issue 
on github at edzer/sfr showed that GPKG can be more effective at handing 
this kind of issue than ESRI Shapefile formats. OGC GPKG should be 
advanced strongly as the preferred modern format eradicating Shapefiles as 
soon as possible (for numerous reasons, including encoding, field name 
lengths, etc.). I don't have a current ESRI license, or I'd try the GPKG 
roundtrip myself. I'd much rather spend time fixing things for GPKG (or 
SQLite) than shapefiles.

Best wishes,

Roger

On Wed, 14 Jun 2017, Shaun Walbridge wrote:

> Glen,
>
> Round-tripping projection information can be tricky, in part because the
> normalization routines vary between different stacks, and what counts
> as the same form is also implementation dependent. In this case
> (round-tripping with ArcGIS), you may be better off using the
> arcgisbinding package [1], which can do the conversion to and from
> ArcGIS native data types (including some that aren't available via
> OGR/GDAL). It's easy enough to install [2], and also lets you build
> Geoprocessing tools which speak directly to R. I imagine there's also a
> pure R solution to the normalization, but it would likely have side
> effects for existing packages, and may not be easily solved.
>
> If you know that your data is fine and want a simple solution, you could
> also just overwrite the new shapefile’s .prj file with a copy of the
> original.
>
> Cheers,
> Shaun
>
> 1. https://urldefense.proofpoint.com/v2/url?u=https-3A__r-2Darcgis.github.io_assets_arcgisbinding.pdf&d=DwIGaQ&c=n6-cguzQvX_tUIrZOS_4Og&r=fCPRb7QX-vd5bnO9gIJHCiX852SVUtyYX--xtCKtpfk&m=9su2o7yjMBqHmqZT3kZAlTRZwPC_W0Tm65yvo7NmjLw&s=pIBxR3icnDLcn639TzBc0mkXy6Tv7G9Ip7xcWSAMweU&e=
> 2. https://urldefense.proofpoint.com/v2/url?u=https-3A__github.com_R-2DArcGIS_r-2Dbridge-2Dinstall&d=DwIGaQ&c=n6-cguzQvX_tUIrZOS_4Og&r=fCPRb7QX-vd5bnO9gIJHCiX852SVUtyYX--xtCKtpfk&m=9su2o7yjMBqHmqZT3kZAlTRZwPC_W0Tm65yvo7NmjLw&s=JADt055JJUuCG1eltd7N9o5f_fu_geqGlnzO62SGtGM&e=
>
> On 6/14/17, 9:35 AM, "R-sig-Geo on behalf of Glenn Stauffer" <r-sig-geo-bounces at r-project.org on behalf of gestauffer at gmail.com> wrote:
>
>    I have a shapefile that I imported into R using readOGR from the rgdal
>    package. I do a little bit of work with it, like adding attribute
>    information, etc, then export it as an ESRI shapefile again, with a new
>    name. However, when I bring both the original and new shapefile into ArcGIS,
>    it tells me that the CRS do not match.
>
>    So, noting that all the projection parameters remain the same, but the
>    projection and coordinate system names are different, and the datum name is
>    dropped, my questions are:
>
>    1.	Is the second CRS the same as the first?
>    2.	If so, why did the names change, and why does ArcGIS no longer
>    recognize it as the same?
>    3.	If not, how did it get changed?
>    4.	Can the proj4string be modified to be more specific, and if so, why
>    did readOGR not already do this to preserve all the information?
>
>    I can use the new shapefiles just fine and readOGR interprets them as
>    identical, but it is a bit vexing that ArcGIS does not. And, I could of
>    course define it again in ArcGIS, but part of the motivation to work in R is
>    to obviate the need to point and click for many files.
>
>    I appreciate any insights or enlightenment.
>
>    Thanks,
>
>    Glenn
>
>    Here is the original projection information from ArcGIS:
>
>    Projected Coordinate System:    NAD_1983_HARN_Transverse_Mercator
>
>    Projection: Transverse_Mercator
>
>    False_Easting:  520000.00000000
>
>    False_Northing: -4480000.00000000
>
>    Central_Meridian:   -90.00000000
>
>    Scale_Factor:   0.99960000
>
>    Latitude_Of_Origin: 0.00000000
>
>    Linear Unit:    Meter
>
>
>
>    Geographic Coordinate System:   GCS_North_American_1983_HARN
>
>    Datum:  D_North_American_1983_HARN
>
>    Prime Meridian:     Greenwich
>
>    Angular Unit:   Degree
>
>    Here is the proj4string from R, which also agrees with the proj4string given
>    for this projection at www.spatialreference.org for epsg:3071 and also for
>    SR-ORG:7396.
>
>    +proj=tmerc +lat_0=0 +lon_0=-90 +k=0.9996 +x_0=520000 +y_0=-4480000
>    +ellps=GRS80 +units=m +no_defs
>
>    When I use writeOGR to export the SpatialPolygonsDataFrame with the above
>    proj4string, then bring it back into ArcGIS, the projection information is
>    given as the following, and is no longer recognized as identical to the
>    original.
>
>    Projected Coordinate System:    Transverse_Mercator
>
>    Projection: Transverse_Mercator
>
>    false_easting:  520000.00000000
>
>    false_northing: -4480000.00000000
>
>    central_meridian:   -90.00000000
>
>    scale_factor:   0.99960000
>
>    latitude_of_origin: 0.00000000
>
>    Linear Unit:    Meter
>
>
>
>    Geographic Coordinate System:   GCS_GRS 1980(IUGG, 1980)
>
>    Datum:  D_unknown
>
>    Prime Meridian:     Greenwich
>
>    Angular Unit:   Degree
>
>
>
>
>
>
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>
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