Hi Joseph,
On Sep 7, 2010, at 8:09 PM, J Glassy wrote:
> Hello,
>
> I'm using v1.8.4-patched on Linux x86_64, and would like to know if
> it is possible to change a fillvalue [ H5Pset_fill_value() ] for a
> dataset, once it has already been "burned in" at creation time?
No, dataset/group/file creation properties are permanent once the
object exists.
> Below I show code for trying to change an existing fillvalue using
> HDF5 ANSI C API, and realize I'm missing something critical about how
> H5Dget_create_plist( {YourDataset_ID} ) works.
The H5<X>get_create_plist call(s) return a _copy_ of the creation
property list for an object. Changing the properties in that list has no
effect on the object.
If you email Francesc Alted (the PyTables author), he might patch in
support for setting the fill value of a dataset.
Quincey
> One motivation for this is that I'd like to use H5Py (v1.3.0) to
> author the dataset, but H5Py does not yet support assigning user
> defined (e.g. non "0") fillvalues as part of a dataset creation call.
> I have a large earth science dataset (in raw binary) that uses a
> fillvalue of -9999.0. If I use H5Py v1.3.0 to initially create these
> HDF5 files, they end up missing the fillvalue. as an example of the
> problem, HDFView and Panoply "see" the pixels coded -9999.0 as valid
> data, which seriously messes up the color palette rendering, among
> other things... I've originally tried using various CF v1.4.x and
> similar standards (e.g. _Fillvalue or missing_data) and verified these
> are distinct from the internal "fillvalue" defined using
> H5Pset_fill_value()...
>
> I realize I could create the dataset using just the HDF5 C API, but
> I've already got the H5Py code about 99% written ..except for this
> lack of fill-value assignment...:))
>
> My example code below shows how I've tried to re-assign a fillvalue
> (on the assumption its possible):
>
> file_id = H5Fopen("test.h5",H5F_ACC_RDWR,H5P_DEFAULT) ;
> /* fetch the dataset id assoc with name "DS1" */
> dset = H5Dopen(file_id,"DS1",H5P_DEFAULT);
>
> /* hid_t H5Dget_create_plist (hid_t dataset_id)
> Returns an identifier for a copy of the dataset creation property list.
> The new property list is created by examining various permanent
> properties
> of the dataset. This is mostly a catch-all for everything but
> type and space. */
>
> int fillval = -8 ;
> dcpl = H5Dget_create_plist(dset);
> status = H5Pset_fill_value (dcpl, H5T_NATIVE_INT, &fillVal);
>
> /* this superfiscially shows the assignment (via dcpl), per se,
> worked correctly...*/
> status = H5Pget_fill_value(dcpl,H5T_NATIVE_INT,&chkfill);
> printf("Status after H5Pget_fill_value %d chkfill %d \n",status,chkfill);
>
> /* but, after the HDF5 file is closed, the new fill value in dcpl
> DOES NOT propogate
> to the physical HDF5 file as hoped...*/
>
> Perhaps someone could point out what's possible and/or where I've
> gone wrong, and indicate a work-around....
>
> thanks much in advance
>
> jmg
>
> ------------------------------------------------------------
> Joseph Glassy
> Lead Software Engineer (contractor)
> NASA Measures (Freeze/Thaw),Rm CFC 424
> College of Forestry and Conservation
> Univ. Montana, Missoula, MT 59812
>
> _______________________________________________
> Hdf-forum is for HDF software users discussion.
> [email protected]
> http://mail.hdfgroup.org/mailman/listinfo/hdf-forum_hdfgroup.org
_______________________________________________
Hdf-forum is for HDF software users discussion.
[email protected]
http://mail.hdfgroup.org/mailman/listinfo/hdf-forum_hdfgroup.org
