spTransform-methods
(Package: rgdal) :
Methods for Function spTransform for map projection and datum transformation in package "rgdal"
The spTransform methods provide transformation between datum(s) and conversion between projections (also known as projection and/or re-projection), from one unambiguously specified coordinate reference system to another, using PROJ.4 projection arguments. For simple projection, when no +datum tags are used, datum projection does not occur. When datum transformation is required, the +datum tag should be present with a valid value both in the CRS of the object to be transformed, and in the target CRS. In general +datum= is to be prefered to +ellps=, because the datum always fixes the ellipsoid, but the ellipsoid never fixes the datum.
readGDAL
(Package: rgdal) :
Read/write between GDAL grid maps and Spatial objects
The functions read or write GDAL grid maps. They will set the spatial reference system if available. GDALinfo reports the size and other parameters of the dataset. create2GDAL creates a GDAL data set from a SpatialGridDataFrame object, in particular to be able to save to GDAL driver formats that only permit copying rather than creation.
SGDF2PCT
(Package: rgdal) :
Convert RGB three band to single band colour table
This function converts a three-band SpatialGridDataFrame into a single band of colour indices and a colour look-up table using RGB2PCT. vec2RGB uses given breaks and colours (like image) to make a three column matrix of red, green, and blue values for a numeric vector.
projInfo
(Package: rgdal) :
List PROJ.4 tag information
The projInfo function lists known values and descriptions for PROJ.4 tags for tag in c("proj", "ellps", "datum", "units"); getPROJ4VersionInfo returns the version of the underlying PROJ.4 release, getPROJ4libPath returns the value of the PROJ_LIB environment variable, projNAD detects the presence of NAD datum conversion tables (looking for conus).
showWKT
(Package: rgdal) :
Show Well-Known Text spatial reference system metadata
Use GDAL/OGR spatial reference objects to convert a PROJ.4 representation to a Well-Known Text representation, and report an EPSG code if it can be determined by OGR SRS services.
The function reads an OGR data source and layer into a suitable Spatial vector object. It can only handle layers with conformable geometry features (not mixtures of points, lines, or polygons in a single layer). It will set the spatial reference system if the layer has such metadata.
providing 
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