inverseSHT implements the inverse SHT from SH coefficients
function (coeffs, aziElev) {
    
    var aziElevR = aziElev;
    var N = Math.sqrt(coeffs.length)-1;
    // SH sampling matrix
    var Y_N = computeRealSH(N, aziElev);
    // reconstruction
    var data = numeric.dotVM(coeffs, Y_N);
    // gather in data matrix
    for (var i=0; i<aziElev.length; i++) {
        aziElevR[i][2] = data[i];
    }
    return aziElevR;
}