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How I can view this .tif file?

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Behzad Navidi
Behzad Navidi on 13 Apr 2020
Commented: Ameer Hamza on 13 Apr 2020
I have a tif file which represents the altitude for a country, I can simply open it in Esri's ArcGIS (Arc Map), Here is the result from ArcMap:
You can see the High and Low elevations are shown by a color range. I used this code below to open this tif file in Matlab:
x = imread('DEM_30s.tif', 'tif');
imshow(x)
But I see a figure like this:
So, If anyone could tell me how I can read my tif file in Matlab with a color bar that specifies high and low elevations (like Arcmap picture above), I would be so grateful.
Note: Since the size of the file is 7 MB, I split it into the 2 part then attach here; I also upload the .tif in my google drive in this link and compressed version of it (.zip) (just one part) here in my google drive.
Thank you

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Behzad Navidi
Behzad Navidi on 13 Apr 2020
I guess I should use demcmap (Colormaps appropriate to terrain elevation data), But I don't know how to use it.

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Accepted Answer

Ameer Hamza
Ameer Hamza on 13 Apr 2020
Edited: Ameer Hamza on 13 Apr 2020
First, the problem is somewhat related to the encoding of your tiff file. The data values are encoded as single-precision numbers, and the background points are encoded as 0xff7fffff in hexadecimal (equal to -3.40282346639e+38, minimum possible number in IEEE754 single-precision floating-point format).
Second, the tiff file only has 1 channel, and have no color information, so you need to create your colormap.
Both problems can be solved by converting the loaded matrix from single to uint16. Note that we are converting the values, not typecasting. Converting to uint16 will convert the background pixels from -3.40282346639e+38 to 0. The elevation values lie in the range [0 - 10000], uint16 is sufficient to hold these values. The integer values will make it an indexed image that can take value from a colormap. Try the following code
[A,R] = readgeoraster('DEM_30s.tif', 'OutputType', 'double');
low_single = typecast(uint8([255 255 127 255]), 'single');
mask = low_single==A;
A = A - min(A(~mask), [], 'all');
% creating colormap changing from white to brown as shown in image in the question
brown_color = [0.8 0.2 0.1];
light_brown = [0.95 0.9 0.8];
t = linspace(0, 1, max(A,[],'all'))';
cmap = t.*brown_color + (1-t).*white;
gs = geoshow(A, cmap, R);
gs.CData(repmat(mask,1,1,3)) = 255;

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Ameer Hamza
Ameer Hamza on 13 Apr 2020
Yes, you are correct. There are depressions in the map. The maximum one at -169 meters. I elevated the whole map by 169 so that they will also have a different color. However, they occupy a tiny region, so they are not easily visible. Also, I have added the line to make the background color white. Please check the updated code. You can add the borderline using the updated code.
Behzad Navidi
Behzad Navidi on 13 Apr 2020
Awesome, Thank you so much ???
Ameer Hamza
Ameer Hamza on 13 Apr 2020
I am glad to be of help.

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