Log Message:
(graphics/R-interp) import R-interp-1.1.4

Bivariate data interpolation on regular and irregular grids, either
linear or using splines are the main part of this package.  It is
intended to provide FOSS replacement functions for the ACM licensed
akima::interp and tripack::tri.mesh functions. Linear interpolation is
implemented in interp::interp(..., method="linear"), this corresponds
to the call akima::interp(..., linear=TRUE) which is the default
setting and covers most of akima::interp use cases in depending
packages. A re-implementation of Akimas irregular grid spline
interpolation (akima::interp(..., linear=FALSE)) is now also available
via interp::interp(..., method="akima"). Estimators for partial
derivatives are now also available in interp::locpoly(), these are a
prerequisite for the spline interpolation. The basic part is a GPLed
triangulation algorithm (sweep hull algorithm by David Sinclair)
providing the starting point for the irregular grid interpolator. As
side effect this algorithm is also used to provide replacements for
almost all functions of the tripack package which also suffers from
the same ACM license restrictions. All functions are designed to be
backward compatible with their akima / tripack counterparts.