MATLAB: How to read grid data from text file

splittext;

hi I have a text file(attached). which contain ozone data. I am not able to read the data. since it is not in regular format. only latitude(-59.5S to 59.5N (1.00 degree steps) ) is given and on every latitude all ozone data is given so there are 288 longitudes(-179.375W to 179.375E (1.25 degree steps)) therefore 288 data points are there. but the problem is all data is in string format and we need to split data after every 3 digit. some random space is also given in the middle of the data so we have to remove that also otherwise data will not split in 3 correct digits .
later i will use inpolygon to grab out the data from specific region. that i will try later. but first i need to read this text file and took the data out.
hope you understand.

Best Answer

The format seems to be GridTOMS as mentioned here. There is an IDL reader and there may be MATLAB ones.
If you need a stable reader, I advise you to look for a MATLAB implementation "endorsed" by NASA. If you need a quick hack to perform early tests, you can try the following (where I assume that spaces code for trailing zeros):
 content = fileread( 'L3_tropo_ozone_column_jan14.txt' ) ;
 % - Remove first space on all data rows.
 content = regexprep( content, '(?<=[\r\n]) ', '' ) ;
 % - Split by "lat = ..." separator.
 blocks = regexp( content, '\s+lat[^\r\n]+', 'split' ) ;
 % - Extract header from block 1.
 pos = regexp( blocks{1}, '\)\s+\d', 'start' ) ;
 header = blocks{1}(1:pos) ;
 blocks{1} = blocks{1}(pos+1:end) ;
 % - Merge blocks, remove \r\n, replace spaces by 0s.
 blocks = [blocks{:}] ;
 blocks = regexprep( blocks, '[\r\n]', '' ) ;
 blocks(blocks == ' ') = '0' ;
 % - Convert to 120x288 numeric array.
 data = reshape( sscanf( blocks, '%3d' ), 288, 120 ).' ;
Note that it is easy to wrap this in a function and call it while iterating through files from a folder (using the output of DIR). It is also easy to extract meta information from the header if relevant.
Related Question