Comments on: Locating the US continental divide, part 1 - Introduction

By: Steve

Steve — Mon, 05 Oct 2009 17:40:19 +0000

Matteo—No problem. That issue gets even experienced users from time to time.

By: Matteo

Matteo — Mon, 05 Oct 2009 17:22:56 +0000

Thank you Steve. Beginner’s mistakes…

By: Steve

Steve — Mon, 05 Oct 2009 15:14:38 +0000

Matteo‐Values in the data files are stored by row, whereas your fread call is filling the output matrix by column. There's a mismatch between the number of columns in the input file and the number of rows you specified in the call to fread, so the data is going to wrap around in funny ways. Try something like this:

B = fread(fid, [10800 4800], precision);
B = B';

multibandread takes care of such details for you.

By: Matteo

Matteo — Sat, 03 Oct 2009 04:48:47 +0000

Hi Steve, great Series. I am trying to use it on tiles A and B to get Canadian continental divide. But I have problems loading data with fread. When I display with imshow it is not right. Upon inspection I noticed columns are arranged in a series 1 to 8 with 9th column the one that should follow column 1. Here is my code.

fid = fopen('b10g','r',byte_order);
[B] = fread(fid,[4800 10800],precision);
fid1 = fopen('a10g','r', byte_order);
[A] = fread(fid1,[4800 10800],precision);
dem = [A,B];
dem_cropped = dem(1500:4000, 6000:16500);
imshow(dem_cropped, display_range);

Do you notice anything wrong?
Thank you so much for any advice.

By: Kazım

Kazım — Sat, 09 May 2009 09:55:55 +0000

Very beatiful work.Thanks for shared.

By: Steve

Steve — Thu, 07 May 2009 17:48:33 +0000

T—You can use fread if you like. multibandread is more convenient to use for many "raw" files, but these are simple enough that fread is pretty easy.

By: T

Thu, 07 May 2009 17:45:41 +0000

What’s the reason for using multibandread instead of fread? I tried it on different (though relatively large) images that also have one “band” and it seems slower than fread…

By: Steve

Steve — Sat, 25 Apr 2009 22:53:27 +0000

Thai—Yes, these data sets are pretty big. I used a 64-bit Linux computer with something like 6 GB of RAM.

By: Thai Hoang

Thai Hoang — Sat, 25 Apr 2009 22:03:04 +0000

My Matlab runs out of memory with this new post.

By: Rich Hoeg

Rich Hoeg — Sat, 25 Apr 2009 14:17:29 +0000

Working with the continental divide in the Rockies is too easy! Your next assignment … map all three major continental watershed divides found in Minnesota! There is one point in northern Minnesota where all three come together (Hudson Bay, St. Lawrence River, Mississippi River). Cheers!