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

[Shaun Walbridge]

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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