Hi Wipneus,
Thanks for putting time and thought into this. It is possible that I have made a mistake somewhere, so I appreciate your efforts to help me track down where I'm messing up. If I am misunderstanding the sea ice grids I certainly want to know what I'm missing.
I am using the SIC data files myself, including the cell area files, but not the lon/lat files. So the possibility of something wrong in those exist. After reading that NSIDC double checked it and found nothing wrong makes that a very small possibility IMO.
That leaves the SIC data files to consider, my first post dealt with that: very unlikely.
In all my judgement is that there is very likely something wrong in your reasoning, unfortunately most of that reasoning is expressed in matlab. That makes it rather difficult to follow and my knowledge of matlab is insufficient to point out where the error lies.
I do not dispute that the figure you posted looks correct, but my argument is that the sea ice concentration grids look good enough when they are plotted alone, but errors become evident when the georeferenced sea ice grids are plotted in context with other datasets. How did you place the dot at McMurdo--by specifying geo coordinates? How did you register the locations of each pixel of the sea ice concentration grid? Can you add a graticule and maybe a coastline from a different dataset to provide context?
No I placed the orange dot manually after consulting a map on wikipedia.
As you agreed that the place is more or less correct, the argument goes as follows:
1) McM lies on the right half side of the map;
2) direct inspection of the longitude values in the pss25lons_v3 array shows that all values in the right half are from 0-180
oConclusion must be that McM lies in the eastern hemisphere. Values could still be incorrect but not like what you found.
Now you might have a look at part 2 of my reasoning. Do you see the same thing? , if not we can talk about why not. A look at this figure from NSIDC documentation may helpful:
Thanks for the note about fread. That's another discrepancy I found between the documentation and the data files. In Matlab,
ci = fread(fid, [316 332]);
is shorthand for
ci = fread(fid, [316 332],'uint8=>double');
and both of the above work well for importing sea ice data. But specifying the 300 byte header skip by
ci = fread(fid, [316 332],'uint8=>double',300);
causes errors. Unfortunately, it's a binary file so we can't just open it and read it directly. That is a whole different complaint of mine--Especially for these small 316x332 grids there is no excuse for encoding the data in binary format. And the data grids are not even in the same format as the corresponding lat, lon grids! Why make the data so inaccessible? Why perpetuate the notion that climate data are locked away in an ivory tower for only the eyes of elite experts to see? Why make it so difficult to debug little georeferencing problems? What poor design.
The 300 bytes is correct I can tell you from experience.
Matlab can do an fseek() call, otherwise a dummy read of 300 bytes should do the trick.
About 300 as argument four in fread, the matlab docs say:
A = fread(fileID, sizeA, precision, skip) skips skip bytes after reading each value
"after", perhaps it skips 300 bytes after each element, so 316x332 times?
