Sunday, January 17, 2010

Converting SIO img file format to Arc ASCII grid w/ Python

Recently I have been battling with getting a SIO binary file format of predicted bathymetery (from Smith/Sandwell satellite topography data) into an Arc-friendly ASCII grid format. GMT has a nifty img2grd command which generates a netcdf of the img file; however, it takes some manual tweaking afterwards to get the coordinate bounds of the data to be Arc-happy (even if one follows img2grd grd2xyz with the -E option). I have decided I want a one-stop solution, where I could just feed in the img file and spit out an ARC ASCII grid and this means I need to write my own script. Therefore, I sat myself down this afternoon and began to teach myself Python (with some input from Kurt). Now, after just a couple hours of Googling, tweaking, and testing, I have a working Python script that does just what I need it to. It reads in an img file, and spits out a space-delimited ASCII grid file complete with the ARC header.

In order to test that I was decoding the binary properly, I wrote the first row of data out to its own little text file and used gnuplot to graph it up.

in my script I have the following:

for i in range(1):
row = struct.unpack('>'+str(ncol)+'h',*ncol))
for depth in row:
print "\n"

then in terminal I call gnuplot and at the prompt type:

plot 'filename' with l

Certainly looks like a nice depth profile to me:

1 comment:

  1. Awesome! This is really helpful. Nice to see you're blogging again :-)