title: How to make RASTER from irregular point data without interpolation
body: <p>I was trying to make a raster image from an irregularly spaced point database. The data looks like-</p>
  
  <pre><code>&gt; 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
  </code></pre>
  
  <p>I want these 'z' values within a mesh which I created by</p>
  
  <pre><code># 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))
  </code></pre>
  
  <p>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: <a href="https://drive.google.com/file/d/0B6GUNg-8d30vYzlwTkhvaHBFTnc/edit?usp=sharing" rel="nofollow">https://drive.google.com/file/d/0B6GUNg-8d30vYzlwTkhvaHBFTnc/edit?usp=sharing</a>
  when I plot</p>
  
  <pre><code>plot(my_mesh)
  points(s100_ras$Y, s100_ras$X, pch="*", col='blue')
  </code></pre>
  
  <p>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!!</p>
  
  <pre><code>library(rgdal)
  library(raster)
  xyz&lt;-cbind(my_mesh, s100_ras)
  r &lt;- rasterFromXYZ(xyz)
  image(r)
  </code></pre>
  
  <p>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!</p>
  
  <pre><code>library(sp)
  s100_ras &lt;- data.frame(expand.grid(x = s100_ras$Y, y = s100_ras$X), 
                         z = as.vector(s100_ras$mean))
  coordinates(s100_ras) &lt;- ~x+y
  proj4string(s100_ras) &lt;- 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
  </code></pre>
  
  <p>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.</p>