OPeNDAP HDF4 Handler Limitations
This new enhanced handler has some limitations. Not all HDF/HDF-EOS2 products can be visualized by the OPeNDAP clients using this handler. Here, we summarize why some NASA products cannot be visualized and list data products that can be visualized by OPeNDAP visualization clients at the end.
Reasons of Visualization Failure
1. Big Size Variable
We found that for big size variable array(>50 MB), the visualization of the variable is very slow. Sometimes, IDV or Panoply may even fail with an out of memory error message.2. Long Variable Name
Some NASA HDF files(e.g., some CERES files) include hundreds of variables and the variable names are long. This will cause the maximum HTTP header size to exceed the default maximum HTTP header size and a failure will occur. To serve those files, please increase the max HTTP header size of your Tomcat server by modifying the following line at server.xml file under the line containing:3. Lambert Azimuthal Equal Area(LAMAZ) Projection
For LAMAZ projection data, the latitude and longitude values retrieved from the HDF-EOS2 library include infinite numbers. So an HDF-EOS2 grid file with LAMAZ projection can not be served correctly.4. Coordinate Variables that do not comply with the CF-convention
There are two common cases. First, some NASA HDF-EOS2 files have missing or fill values inside latitude and longitude coordinate variables. Except the HDF-EOS2 geographic(a.k.a. equidirectional, equirectangular, equidistant cylindrical) projection, clients may not display the data correctly. Second, if NASA HDF-EOS2 files have 3-D latitude and longitude coordinate variables, clients may not display the data correctly. However, there is One exception: some CERES products can be visualized and they are listed in Table 1 below.5. Pure HDF4 Files
All pure HDF4 (i.e., non-HDF-EOS2) products we've tested are listed in Table 1 below. Other pure HDF4 products are not tested and may not be visualized by Java OPeNDAP clients.Other Limitations
1. HDF-EOS2 Files having additional HDF4 Vdata Objects
Some HDF-EOS2 files have additional HDF4 objects. The HDF4 object may be either Vdata or SDS. That means, some contents are added to an HDF-EOS2 file by using the HDF4 APIs directly after the HDF-EOS2 file is created using the HDF-EOS2 APIs. Thus, the HDF-EOS2 API may not retrieve information about the added HDF4 objects. Up to this release, we found those information are mainly related to metadata and those metadata may not be critical to visualize and analyze the real physical data variables. So in this release, such Vdata objects are currently ignored and only SDS objects are mapped. Please note that the attributes of existing HDF-EOS2 data variables are not ignored.2. 3-D or 4-D Variables
Some variables stored as 3-D or 4-D arrays are either missing or hard to find the third and/or fourth dimension's coordinate variable. In this case, the handler uses integer number (1,2,...,n) to represent the third and/or fourth dimension as levels. Clients can still visualize the data in a horizontal plane level by level.3. Metadata for CERES Product
To speed up the performance, we chose not to generate structMetadata, coreMetadata, and archiveMetadata attributes for some CERES products. For applications that need these, please contact eoshelp@hdfgroup.org. You can also post a message at http://hdfeos.org/forums.List of Supported Data Product
The following NASA HDF-EOS2 and HDF4 products are tested with IDV and Panoply. Please check the above sections for the limitations.
Table 1. NASA HDF-EOS2/HDF4 Data Products supported by the Enhanced HDF4 Handler| NASA Data Centers | Products | Type |
|---|---|---|
| GES DISC | AIRS/MERRA/TOMS | HDF-EOS2 |
| LAADS/LP DAAC/NSIDC | Many MODIS | HDF-EOS2 |
| LaRC | MISR/MOPITT/CERES-TRMM | HDF-EOS2 |
| GES DISC | TRMM Level 1B, Level 2B Swath TRMM Level 3 Grid 42B and 43B | HDF4 |
| OBPG (Ocean Color) | SeaWiFS/MODIST/MODISA/CZCS/OCTS level 2 and level 3m(l3m) | HDF4 |
| LaRC |
CER_AVG_Aqua-FM3-MODIS,CER_AVG_Terra-FM1-MODIS CER_ES4_Aqua-FM3_Edition1-CV or similar one CER_ISCCP-D2like-Day_Aqua-FM3-MODIS or similar one CER_ISCCP-D2like-GEO_ or similar one CER_SRBAVG3_Aqua or similar one CER_SYN_Aqua or similar one CER_ZAVG or similar one | HDF4 |
| PO.DAAC | AVHRR | HDF4 |
- - Last modified:May 16th 2011