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

[Glenn Stauffer]

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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