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BEAM HDF file compatibility
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BEAM HDF file compatibility
6/16/10 3:45 PM
Hello,

From my understanding BEAM can open only specific HDF files (e.g. NASA OBPG L2); can BEAM be tricked into opening my IDL generated HDF files so that image data is represented under ‘bands’ etc? Do I need to copy the format of an Ocean Color HDF file to do this?

Also, will I be able to add geo-coding to the pixels if the latitude/longitude are provided in the file?

Many thanks,
Chris

EDIT: Or is there more flexibility when using NET-CDF files?
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RE: BEAM HDF file compatibility
6/17/10 8:30 AM as a reply to Chris Kent.
Hi Chris

If possible I would suggest to write NetCDF files. These files should follow the CF-conventions.
Another possibility is to write GeoTIFF files, if you can do this with IDL.

If you have latitude/longitude bands in your files you can attach them as PixelGeoCoding to the product.


best wishes
Marco
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RE: BEAM HDF file compatibility
8/3/10 11:58 AM as a reply to Marco Peters.
Hi Marco,

I have generated some NetCDF-4 files using IDL 8.0 however when trying to open them in BEAM VISAT 4.8 I recieve the error that there is no appropriate reader. I have also tried the products as NetCDF-3 (classic) format but receive the same error. I note that other programs such as HDFexplorer can read the products, and using NCDUMP does not show any problems with the files. The same files generated with NCGEN however also cannot be opened.

I initially tried this with a numebr of variables etc but it also won't open files with only global attributes.Strangely I was able to open the products in BEAM 4.7.1 yesterday but now (with no changes to my generation code) even this is unavailable.

Is there a specific flag/attribute that BEAM uses to select the NetCDF reader?

Many thanks for your help,
Regards,

Chris
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RE: BEAM HDF file compatibility
8/3/10 12:55 PM as a reply to Chris Kent.
Ok, the plot thickens!!

I can now get the NetCDF-4 products to open with Beam VISAT 4.7.1 (a local problem on my machine reading from a network drive), however the products still do not open with BEAM 4.8; I now receieve the error:

"Type: jave.lang.NullPointerException,
No message text available"

Any ideas?

Many thanks,
Chris
Flag Flag
RE: BEAM HDF file compatibility
8/3/10 1:48 PM as a reply to Chris Kent.
Hi Chris,

We've changed a lot in the NetCDF reader. We tried to preserve the compatibility. Probably there are some edge cases in which the reader fails.
In general if you NetCDF file is follows the CF-Convention it should be readable.
Could you upload the file to our ftp-server. I'll send you the log in data separately via mail.

best wishes
Marco
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RE: BEAM HDF file compatibility
8/3/10 4:56 PM as a reply to Chris Kent.
I found that the problem is that two of the bands in your product contain a dot.
We missed to escape the band name when searching for the corresponding NetCDF variable.

As a workaround you should not use dots '.' and slashes '/' in variable names until we provide an update.

By the way, I have seen that one of the band names is 'casi_lat' and the other is 'csai_lon'. Probably a typo.

best wishes
Marco
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RE: BEAM HDF file compatibility
8/3/10 5:40 PM as a reply to Marco Peters.
Hi Marco,

Thank you very much for your help - my products are now working in BEAM 4.8.

Sorry, I do have more quick question though.

My data is set as short integers with the scaling factor and offset as floats at 0.001 and 0.0 respectively, however BEAM is representing the data incorrectly; for example 0.03500000014901161 instead of the expected 0.035. This does not occur at all points and appears to be representing the numbers as double precision with rounding/truncation errors?

Although the additional numbers have very little effect on the absolute pixel value, is there a workaround for this?

Cheers,
Chris
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RE: BEAM HDF file compatibility
8/4/10 9:20 AM as a reply to Chris Kent.
Unfortunately there is no workaround for this rounding error.

best wishes
Marco
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