# Converting lots of raster files from one reference system to another

I had to convert lots of OSGB EPSG:27700 raster files to LonLat EPSG:4326 format and here is how I did it on my OSX terminal. I also wanted to change the format from *.asc to *.tif. Supposing you already have gdal libraries installed, just run the following code:

To utilise all CPUs, add -wo NUM_THREADS=ALL_CPUS to the gdalwarp options.

You can modify the for loop to rename lots of files. Here, I am rename them from *.max to *.asc.