How to make RASTER from irregular point data without interpolation

I was trying to make a raster image from an irregularly spaced point database. The data looks like- ``` > head(s100_ras) x y z 1 267573.9 2633781 213.29545 2 262224.4 2633781 69.78261 3 263742.7 2633781 51.21951 4 259328.4 2633781 301.98413 5 264109.8 2633781 141.72414 6 255094.8 2633781 88.90244 ``` I want these 'z' values within a mesh which I created by ``` # Create a fine mesh grid my_mesh=expand.grid(seq(min(s100_ras$Y),max(s100_ras$Y),l=100), seq(min(s100_ras$X),max(s100_ras$X),l=100)) ``` I also want the z-values to be assigned as 'NA' for those mesh points that are outside the data points. The points over the mesh looks like this: https://drive.google.com/file/d/0B6GUNg-8d30vYzlwTkhvaHBFTnc/edit?usp=sharing when I plot ``` plot(my_mesh) points(s100_ras$Y, s100_ras$X, pch="*", col='blue') ``` The problem is that I'm not sure how to build on this, the following steps don't work because my mesh grid and data points are not of the same scale!! ``` library(rgdal) library(raster) xyz<-cbind(my_mesh, s100_ras) r <- rasterFromXYZ(xyz) image(r) ``` If I try to make a raster just by using the data points (without any mesh), R throws an error since my data is irregularly spaced! ``` library(sp) s100_ras <- data.frame(expand.grid(x = s100_ras$Y, y = s100_ras$X), z = as.vector(s100_ras$mean)) coordinates(s100_ras) <- ~x+y proj4string(s100_ras) <- CRS("+proj=utm +zone=46 +datum=WGS84") gridded(s100_ras) = TRUE suggested tolerance minimum: 0.916421 Error in points2grid(points, tolerance, round) : dimension 1 : coordinate intervals are not constant ``` Moreover, I was trying to play with 'rasterize' function (for irregular grids) of 'raster package', but couldn't get a way with it :(. I know how to interpolate and make a regular grid, but for the sake of originality, I want to AVOID interpolation. Is it possible to make a raster of irregularly spaced data points without idw or kriging methods? Thanks in advance.