HDF Scientific Dataset ID Numbers
IDL's HDF_SD_ routines can accept two different types of ID numbers. Documentation for these routines in the
IDL Reference Guide
refers to these ID numbers as the
SD_ID
and
SDS_ID
arguments.
The
SD_ID
is the Scientific Dataset interface ID. There is only one
SD_ID
per HDF file. For each actual dataset used, you will also need an
SDS_ID
, which is the ID for the particular dataset.
Some routines, such as HDF_SD_ATTRFIND accept either an
SD_ID
or an
SDS_ID
. In these cases, the documentation refers to the ID as an
S_ID
, meaning that either type of ID is accepted.
A Cautionary Note about Tags
Both the old DFSD and the new MFSD HDF interfaces use the same tags. Therefore, you must be careful when reading or writing SDs. Use only the appropriate "HDF_SD_" or "HDF_DFSD_" routines. The wrong SD interface may seem to work, but may return bad results.
IDL and HDF Data Types
HDF and IDL support many different data types. Many of the HDF routines allow you to perform a data type conversion "on the fly" by setting keywords such as FLOAT. When the data type desired is not explicitly specified, IDL uses the conversions shown in the following tables. Note that single-precision floating-point is the default data type and that the complex data type is not supported.
When writing IDL data to an HDF file, IDL data types are converted to the HDF data types shown in
See Type Conversions when Writing IDL Data to an HDF File
:
-
Type Conversions when Writing IDL Data to an HDF File
|
IDL Data Type
|
HDF Data Type
|
|
BYTE
|
DFNT_UINT8 (IDL bytes are unsigned)
|
|
INT
|
DFNT_INT16
|
|
LONG
|
DFNT_INT32
|
|
FLOAT
|
DFNT_FLOAT32
|
|
DOUBLE
|
DFNT_DOUBLE
|
|
STRING
|
DFNT_CHAR
|
When reading data from an HDF file, HDF data types are converted to the IDL data types shown in
See Type Conversions when Reading HDF Data into IDL
:
-
Type Conversions when Reading HDF Data into IDL
|
HDF Data Type
|
IDL Data Type
|
|
DFNT_CHAR or DFNT_UCHAR
|
STRING
|
|
DFNT_INT8 or DFNT_UINT8
|
BYTE
|
|
DFNT_INT16 or DFNT_UINT16
|
INT
|
|
DFNT_INT32 or DFNT_UINT32
|
LONG
|
|
DFNT_FLOAT32 or DFNT_NONE
|
FLOAT
|
|
DFNT_DOUBLE
|
DOUBLE
|
HDF type codes for the supported HDF data types are shown in
See HDF Data Type Codes
:
|
HDF Data Type
|
Type Code
|
|
DFNT_UCHAR
|
3
|
|
DFNT_CHAR
|
4
|
|
DFNT_FLOAT32
|
5
|
|
DFNT_DOUBLE
|
6
|
|
DFNT_INT8
|
20
|
|
DFNT_UINT8
|
21
|
|
DFNT_INT16
|
22
|
|
DFNT_UINT16
|
23
|
|
DFNT_INT32
|
24
|
|
DFNT_UINT32
|
25
|
Common HDF Tag Numbers
Common HDF Tag Numbers
lists
common HDF tag numbers and their meanings.
|
Tag Number
|
Meaning
|
|
030
|
Version Identifier
|
|
100
|
File Identifier
|
|
101
|
File Description
|
|
102
|
Tag Identifier
|
|
103
|
Tag Description
|
|
104
|
Data Identifier Label
|
|
105
|
Data Identifier Annotation
|
|
106
|
Number Type
|
|
107
|
Machine Type
|
|
200
|
Obsolete
|
|
201
|
Obsolete
|
|
202
|
Obsolete
|
|
203
|
Obsolete
|
|
204
|
Obsolete
|
|
300
|
RIG Image Dimension
|
|
301
|
Raster Image Look Up Table (LUT)
|
|
302
|
Raster Image
|
|
303
|
Compressed Raster Image
|
|
306
|
Raster Image Group (RIG)
|
|
307
|
RIG LUT Dimension
|
|
308
|
RIG Matte Dimension
|
|
309
|
Raster Image Matte Data
|
|
310
|
Raster Image Color Correction
|
|
311
|
Raster Image Color Format
|
|
312
|
Raster Image Aspect Ratio
|
|
400
|
Composite Image Descriptor
|
|
500
|
XY Position
|
|
602
|
Vector Image - Tek4014 Stream
|
|
603
|
Vector Image - Tek4105 Stream
|
|
701
|
SD Dimension Record
|
|
702
|
SD Data
|
|
703
|
SD Scales
|
|
704
|
SD Labels
|
|
705
|
SD Units
|
|
706
|
SD Formats
|
|
707
|
SD Max/Min
|
|
708
|
SD Coordinates
|
|
710
|
SD Link
|
|
720
|
SD Descriptor (NDG)
|
|
731
|
SD Calibration Information
|
|
732
|
SD Fill Value
|
|
1962
|
Vdata Description
|
|
1963
|
Vdata
|
|
1965
|
Vgroup
|
