I'm looking for a process to convert ASCII gridded data (in this case 60min/1 degree gridded ASCII population data (GPW) from SEDAC: https://sedac.ciesin.columbia.edu/data/set/gpw-v4-population-count-adjusted-to-2015-unwpp-country-totals-rev11/data-download) to a CSV with three columns: lon, lat, and value using open source tools.
This is the data header:
ncols 360 nrows 180 xllcorner -180 yllcorner -90 cellsize 1.0000000000001 NODATA_value -9999
so the data is structured as space-separated values, with each value occupying a position within 360 columns and 180 rows that represents its coordinates via that position:
-9999 -9999 -9999 -9999 -9999 -9999 0.000936705 0.002529013 0.001377391 0.001723122 0.0004472999 ...
I only want to include positive values in the lon/lat CSV.
I've been using GDAL for other tasks and have been looking in the documentation, but I'm not seeing this type of data manipulation in its scope.