Dear list,
I am a unsure if I am specifying my projection information correctly. I have a shapefile (from Hydro1K data). The projection information in the readme is described as:
Projection used:  Lambert Azimuthal Equal Area
                  Units = meters
                  Pixel Size = 1000 meters
                  Radius of Sphere of Influence = 6,370,997 meters
                  Longitude of Origin = 20 00 00E
                  Latitude of Origin = 5 00 00N
                  False Easting = 0.0
                  False Northing = 0.0

Looking at information in the readme and the associated .prj file I set the projection information like so:
proj <- CRS("+proj=laea +lon_0=20 +lat_0=5 +ellps=sphere") #the ellps 'sphere' has a radius of 6370997.0m
projection( myshpfile ) <- proj

However, I was wondering, do I also need to specify a datum? Or is the above specification ok? In the .prj file it says:
DATUM["D_Sphere_ARC_INFO",SPHEROID["Sphere_ARC_INFO",6370997.0,0.0]]
But I am not sure what datum this refers to? Does anyone know? Or can tell me where to find out?

I also have some data which is in geographic coordinates. The .prj file of this data states:
GEOGCS["GCS_WGS_1984",DATUM["D_WGS_1984",SPHEROID["WGS_1984",6378137.0,298.257223563]],PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433]]

So am I correct in thinking that the projection information for this should be:
projgeo <- CRS("+proj=latlong +datum=WGS84 +ellps=WGS84")
projection(mygeoshpfile) <- projgeo

Then to convert mygeoshpfile to the same projection as myshpfile I can use spTransform like this:
mygeoshpfile2 <- spTransform(mygeoshpfile, proj)

I want to make sure I am accurately converting from one projection to the other. Do I need to specify further proj parameters?

Many thanks,

Simon

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