Matrix of first set of locations where each row gives the
coordinates of a particular point.
x2
Matrix of second set of locations where each row gives the
coordinates of a particular point.
delta
only distances smaller than delta are recorded,
see Details.
miles
For great circle distance: If true distances are in statute miles if false distances in
kilometers.
R
Radius to use for sphere to find spherical distances. If NULL
the radius is either in miles or kilometers depending on the
values of the miles argument. If R=1 then distances are of
course in radians.
Value
A spam object containing the distances spanned between
zero and delta. The sparse matrix may contain many zeros
(e.g., collocated data). However, to calculate covariances, these zeros
are essential.
Details
These functions are wrappers to rdist and
rdist.earth in fields. They are used
to simplify the use of sparse matrices in functions like mKrig.
For great circle distance, the matrices x1 and x2
contain the degrees longitudes in the first and the degrees latitudes
in the second column. delta is in degrees. Hence to restrict
to distances smaller than delta.km, one has to specify
delta=delta.km*360/(6378.388*2*pi).