[R-sig-Geo] is raster terrain accurate for WGS84 tiles?

Robert J. Hijmans r.hijmans at gmail.com
Wed Aug 12 20:40:35 CEST 2015

I do not think it is wishful thinking. Au contraire, I think it is how
it should be done. That is, if you start with a longitude/latitude
raster with elevation values, and want slopes (or similar) also in
that coordinate reference system, then this should be the way to go,
as you skip two transformations, each of which would lead to data
quality loss.

((for the record, the question is about computing slopes from raster
data with a longitude/latitude (angular) coordinate reference system
---- the datum 'WGS 84'  is not relevant, as projected data also use
that datum))

On Wed, Aug 12, 2015 at 10:44 AM, Stanley, Thomas A.
(GSFC-617.0)[USRA] <thomas.a.stanley at nasa.gov> wrote:
> At https://rpubs.com/ajlyons/rspatialdata, a presentation shows the raster package's terrain function used directly on an unprojected raster near the Equator. I'd love to skip the steps of projecting and unprojecting my DEM tiles (eg http://www.viewfinderpanoramas.org/dem3/M11.zip), but I'm not sure the function is intended to be used in WGS 84 for all locations. The output values certainly look good. Can I correctly calculate slope without projecting my tiles, or is that wishful thinking?
> -Thomas
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