proj4string doesn't seem to completely define ESRI projection information

Question

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 does 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 questionas 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, but it would be nice to know that the CRS is identical to the original. 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.

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 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

Answer 1

Perhaps not a definitive answer, but I posted this question on the R-sig-Geo list serve, and got a few possible work-around solutions. For now, I simply used an R-script to overwrite the .prj file with a copy of the original, and that seems to work fine. Also suggested was the use of a package called arcgisbinding to bridge ArcGIS and R (and maybe a similar solution would be available for QGIS?). I have not verified the arcgisbinding solution, but more information can be found at the the blog post here and in the package documentation here.