[gdal-dev] Does gdal_calc.py not calculate arithmetic with in the same file?

[Jeremy Palmer]

Hi Cleo,

Just been dealing with this type of issue.

It’s likely that the byte datatype is overflowing.

Try something like:

--calc "(A.astype(int)-B.astype(int))/(A.astype(int)+B.astype(int))"

Actually you might only need to cast one of the bands from byte to int, so the syntax could be:

--calc "(A.astype(int)-B A.astype(int)+B)"

Cheers
Jeremy

From: gdal-dev-bounces at lists.osgeo.org [mailto:gdal-dev-bounces at lists.osgeo.org] On Behalf Of Cleo Drakos
Sent: Wednesday, 30 July 2014 2:06 p.m.
To: Vincent Schut
Cc: gdal-dev
Subject: Re: [gdal-dev] Does gdal_calc.py not calculate arithmetic with in the same file?

Even if I converted the input file into Float 32 at first, the resulted image is still totally black.

cleo

On Tue, Jul 29, 2014 at 11:20 PM, Vincent Schut <schut at sarvision.nl<mailto:schut at sarvision.nl>> wrote:
On 07/29/2014 04:04 PM, Cleo Drakos wrote:

Thanks for your response.
I tried the followings:

gcalc = 'C:\\Users\\cleo\\Documents\\gdalpys\\gdal_calc.py'
##I produced second file (b)as the copy of first(a)
a = 'D:\\a.tif'
b = 'D:\\b.tif'
outfile = 'D:\\result.tif'
expr = '(A-B)/(A+B)'
subprocess.call([sys.executable,gcalc,'-A',a,'--A_band','1','-B',b,'--B_band','0','--outfile',outfile,\
    '--calc',expr,'--type','Float32','--format','ENVI'],shell=True)
a,b,outfile = None, None,None

Unfortunately, resulted file is completely black.

I hope someone can help me.

I don't use gdal_calc myself, but I suppose the problem is the byte datatype. I would try to convert the input data to float32 first (use gdal_translate -ot Float32) and try again.

Best,
Vincent.




On Tue, Jul 29, 2014 at 10:37 PM, Etienne Tourigny <etourigny.dev at gmail.com<mailto:etourigny.dev at gmail.com>> wrote:
I am not sure, but you can do the following to make sure:

cp infile infile2
gdal_calc.py -A infile --A_band 1 -B infile2 --B_band 0 --outfile outfile --calc "(A-B)/(A+B)"

Also, perhaps the extra comma in your command might be to blame "-B infile,"

Etienne

On Tue, Jul 29, 2014 at 3:46 AM, Cleo Drakos <cleo21drakos at gmail.com<mailto:cleo21drakos at gmail.com>> wrote:
Hi GDAL Developers,

I have one GeoTIFF file with 2 bands. The data type is Byte. I want to calculate (Band2-Band1)/(Band2+Band1).

But the following command provided a dark image:

gdal_calc.py -A infile --A_band 1 -B infile, --B_band 0 --outfile outfile --calc "(A-B)/(A+B)"

Does gdal_calc.py not calculate arithmetic with in the same file?

Thanks for your time.

cleo

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