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Re: Question regarding HDF file [message #55212 is a reply to message #55144]

Tue, 07 August 2007 10:43

James Kuyper
Messages: 425
Registered: March 2000

Senior Member

None wrote:
>>> HDF_SD_GETDATA, sdsIDsm, rr, start=[0,0], count=[x[j],y[j]],
>>> stride=[0,0]
>>
>> HDF_SD_GetInfo, sdsIDsm, NAME=name, HDF_TYPE=htype, TYPE=itype
>> PRINT, im[j], name, htype, itype, min(rr), max(rr)
>>
>>> HDF_SD_GETDATA, sdsIDsm2, r2
>>
>> HDF_SD_GetInfo, sdsIDsm2, NAME=name, HDF_TYPE=htype, TYPE=itype
>> PRINT, bd[j], name, htype, itype, min(r2), max(r2)
>>
>> PRINT, min(rowp), max(rowp)
>>
>
> Hi. I did the corrections which you had mentioned, but still I am
> getting the same results. I also changed the !PI and !DTOR.

Those were debugging printouts, not corrections. They're not intended
to solve the problem, they're intended to help figure out what the
problem is.

> I have changed it to read from the variable directly instead writing
> to the text file and again reading from it. these are the information
> which I got.
>
> sdsIDsm= 9 ImageData DFNT_UINT8 BYTE 40 249
> sdsIDsm2= 10 RadiometricCorrTable DFNT_FLOAT32 FLOAT
> -3.57843 2.47200
>
> Max(rowp) & Min(rowp) = 0.506396 0.000000

I see a very serious problem right here, and it's a problem at the
design level, not at the level of coding. You're attempting to write
floating point values that range from 0.0 to 0.5 to an output array
whose type is an 8-bit unsigned integer. The best you can hope for is
automatic conversion from the floating point value to the 8-bit
unsigned integer; that would result in the output array being filled
with 0s.

IDL> filename = 'test.hdf'
IDL> sd_name = 'Bytes'
IDL> file = HDF_SD_Start(filename, /CREATE)
% Loaded DLM: HDF.
IDL> Dims = [30,40]
IDL> sds = HDF_SD_Create(file, sd_name, dims, /DFNT_UINT8)
IDL> data = BYTE(40+randomu(Seed, dims)*209)
IDL> print,min(data),max(data)
40 248
IDL> HDF_SD_AddData, sds, data
IDL> HDF_SD_EndAccess, sds
IDL> HDF_SD_End,file

IDL> file = HDF_SD_Start(filename, /RDWR)
IDL> idx = HDF_SD_NameToIndex(file, sd_name)
IDL> sds = HDF_SD_Select(file, idx)
IDL> fdata = 0.506396*randomu(Seed, dims)
IDL> HDF_SD_AddData, sds, fdata
IDL> HDF_SD_EndAccess, sds
IDL> HDF_SD_End, file

IDL> idx = HDF_SD_NameToIndex(file, sd_name)
IDL> sds = HDF_SD_Select(file, idx)
IDL> HDF_SD_GetData,sds, data
IDL> print, min(data), max(data)
0 0
IDL> HDF_SD_EndAccess, sds
IDL> HDF_SD_End, file

> But if i open the hdf file, I am getting values like -3.5123 -1.5232
> -3.5138 .............

How exactly are you reading the file? If you use the same methods
shown in this code, you should be reading in the ImageData SDS as a
BYTE array, which should have such values.

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[Message index]

		Question regarding HDF file By: None[1] on Sun, 05 August 2007 12:50
		Re: Question regarding HDF file By: James Kuyper on Tue, 07 August 2007 14:55
		Re: Question regarding HDF file By: None[1] on Wed, 08 August 2007 09:37
		Re: Question regarding HDF file By: None[1] on Tue, 07 August 2007 14:25
		Re: Question regarding HDF file By: James Kuyper on Tue, 07 August 2007 10:52
		Re: Question regarding HDF file By: James Kuyper on Tue, 07 August 2007 10:43
		Re: Question regarding HDF file By: None[1] on Tue, 07 August 2007 08:21
		Re: Question regarding HDF file By: James Kuyper on Mon, 06 August 2007 14:30
		Re: Question regarding HDF file By: James Kuyper on Wed, 08 August 2007 18:02

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