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

Wed Jun 14 19:23:43 CEST 2017

Thanks Shaun, 
I have not gotten the arcgisbinding package to work yet, and will play around with it some more later. For now, overwriting the .prj file works just fine and does what I want, but it seems like a less-than-satisfactory general solution.

Glenn 

-----Original Message-----
From: Shaun Walbridge [mailto:SWalbridge at esri.com] 
Sent: Wednesday, June 14, 2017 10:14 AM
To: Glenn Stauffer; r-sig-geo at r-project.org
Subject: Re: [R-sig-Geo] proj4string read by readOGR doesn't seem to precisely specify source shapefile projection

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=5UpQjHXPqFUScg58BUIFe0V27sq0j0SU7iU72HpYMRE&m=_FSAFRAGaC_k8hnGwM32OZirmWVi4Y5JSgcMf6lcemc&s=_ZSX1hSgmnuhYzWoUo1N-3o_6nKHXkyG4VwSmOB276M&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=5UpQjHXPqFUScg58BUIFe0V27sq0j0SU7iU72HpYMRE&m=_FSAFRAGaC_k8hnGwM32OZirmWVi4Y5JSgcMf6lcemc&s=xV9M4ZmMdIeeGjFZaKaEt-SQA4CAvcB0_UWCjm-qUX0&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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