getProjectionMatrix: Calculate projection matrix to translate one grid to another

In RCMIP5: Tools for Manipulating and Summarizing CMIP5 Data

Description

The bulk of the computational time for regridding lies in calculating the area-weighted projection matrix. This functions allows you to pre-calculate the projection matrix to speed up regridding.

Usage

getProjectionMatrix(orgArea, projArea, verbose = FALSE)

Arguments

orgArea	A cmip5data object or list with lat (latitude) and lon (longitude) matrices of the orginal grid
projArea	A cmip5data object or list with lat (latitude) and lon (longitude) matrices of the projection grid
verbose	logical. Print info as we go?

Details

This function calculates the projection matrix to shift one global grid to a second. The relative contribution of an old grid to the new grid is calculated via an area weighting scheme where the area of a grid cell is assumed to be proportional to the degree area of that cell and neighboring cells are assumed to have the same area to degree ratios. This will NOT hold in large grids. Nor is the area weighting scheme appropriate for all variable types and grid shifts. Use with caution.

See Also

regrid

Examples

numOrgLon <- 3
numOrgLat <- 3
orgLon <- matrix(seq(0, 360-360/numOrgLon, by=360/numOrgLon) + 360/numOrgLon/2, 
                 nrow=numOrgLon, ncol=numOrgLat)
orgLat <- matrix(seq(-90, 90-180/numOrgLat, by=180/numOrgLat) + 180/numOrgLat/2, 
                 nrow=numOrgLon, ncol=numOrgLat, byrow=TRUE)
orgArea <- list(lon = orgLon, lat=orgLat)

numProjLon <- 2
numProjLat <- 2
projLon <- matrix(seq(0, 360-360/numProjLon, by=360/numProjLon) + 360/numProjLon/2, 
                 nrow=numProjLon, ncol=numProjLat)
projLat <- matrix(seq(-90, 90-180/numProjLon, by=180/numProjLon) + 180/numProjLon/2, 
                 nrow=numProjLon, ncol=numProjLat, byrow=TRUE)
projArea <- list(lon = projLon, lat=projLat)

transferMatrix <- getProjectionMatrix(orgArea = orgArea, projArea=projArea)

RCMIP5 documentation built on May 1, 2019, 6:28 p.m.