mrtsSphere - Multi-Resolution Thin-Plate Splines on the Sphere

Constructs multi-resolution thin-plate spline (MRTS) basis functions on the sphere and fits the corresponding multi-resolution mixed model (MRMM) by generalised least squares with a tapered Matérn residual covariance, including kriging-style prediction with closed-form standard errors. Implements the system described in Huang, Huang, and Ing (2025) "Multi-Resolution Spatial Methods on the Sphere: Efficient Prediction for Global Data", Environmetrics, <doi:10.1002/env.70092>. Heavy basis computations are written in 'C++' via 'Rcpp' with optional 'OpenMP' parallelism.