| Re: Getting mean from HDF SD files - stack in envi or read into IDL array? [message #61163 is a reply to message #61071] |
Sat, 05 July 2008 08:46   |
kathryn.davies1
Messages: 4
Registered: July 2008
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Junior Member |
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On Jul 5, 4:33 pm, bulrushmo...@gmail.com wrote:
> On Jul 4, 8:41 am, kathryn.davi...@googlemail.com wrote:
>
>
>
>
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>> Hi
>
>> I am extremely new to IDL (2 weeks!) and have previously only used
>> envi on a small scale.
>
>> I want to read one SD dataset from from a each of a huge number of
>> MODIS files and having looked at IDL and envi batch routines can't
>> decide which is the best way. Bear in mind my limited knowledge and a
>> very short timeframe.... Should I write an envi batch programme and
>> create a big (3000bands +) envi file or should I put straight into the
>> an IDL array. I need to get a mean value (one image or array) and
>> even if it is easier in envi batch mode, would the routine
>> ENVI_SUM_DATA_DOIT with the Mean option deal with the missing
>> values???
>
>> Looking at IDL I have managed to open HDF file from command line, read
>> in appropriate data set to an array but how then could I build 3D
>> array from absolutely loads of 2D arrays.
>
>> Big questions I know - I am desperate to do this in a short time.
>
>> Any help on any aspect much appreciated.
>
>> K
>
> Tell me more about how many bands you have in HDF file and how many
> bands you want to read into IDL?- Hide quoted text -
>
> - Show quoted text -
Well I am going to be using around 3-4000 MODIS HDF files but I only
want one band (the first) from each i.e. the Land Surface
Temperature. Since my last post I have thought about creating a huge
multiband file in ENVI and then exporting as a variable to IDL (if the
ENVI_SUM_DOIT doesn't work for the mean, as it may not deal with
missing values very well, I need them to not be counted as opposed to
counting as zero). However that means extracting the SD dataset from
all of the HDF files, converting them to ENVI standard files to build
multi-band image. I hope the data values are not corrupted by being
converted to ENVI standard. Also I could create an image stack in
iIMAGE or mess about with iDataManager in some way but they do not
seem to like reading ENVI standard files and keep asking me to fill in
binary information - will the data values still be OK?
Thanks
Kathryn
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