vendor: OpenCV 5.0.0 snapshot at 755e50675d97db9b7d449d8bd6b09888646f6c6e

2026-08-22 00:11:13 +08:00
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+Creating Groups {#tutorial_hdf_create_groups}
+===============================
+
+Goal
+----
+
+This tutorial will show you:
+ - How to create a HDF5 file?
+ - How to create a group?
+ - How to check whether a given group exists or not?
+ - How to create a subgroup?
+
+Source Code
+----
+
+The following code creates two groups: `Group1` and `SubGroup1`, where
+`SubGroup1` is a child of `Group1`.
+
+You can download the code from [here][1] or find it in the file
+`modules/hdf/samples/create_groups.cpp` of the opencv_contrib source code library.
+
+@snippet samples/create_groups.cpp tutorial
+
+Explanation
+----
+
+First, we create a HDF5 file
+
+@snippet samples/create_groups.cpp tutorial_create_file
+
+If the given file does not exist, it will be created. Otherwise, it is open for read and write.
+
+Next, we create the group `Group1`
+
+@snippet samples/create_groups.cpp tutorial_create_group
+
+Note that we have to check whether `/Group1` exists or not using
+the function cv::hdf::HDF5::hlexists() before creating it. You can not create
+a group with an existing name. Otherwise, an error will occur.
+
+Then, we create the subgroup named `Subgroup1`. In order to
+indicate that it is a sub group of `Group1`, we have to
+use the group name `/Group1/SubGroup1`:
+
+@snippet samples/create_groups.cpp tutorial_create_subgroup
+
+Note that before creating a subgroup, we have to make sure
+that its parent group exists. Otherwise, an error will occur.
+
+In the end, we have to close the file
+
+@snippet samples/create_groups.cpp tutorial_close_file
+
+Result
+----
+
+There are many tools that can be used to inspect a given HDF file, such
+as HDFView and h5dump. If you are using Ubuntu, you can install
+them with the following commands:
+
+@code
+sudo apt-get install hdf5-tools hdfview
+@endcode
+
+There are also binaries available from the The HDF Group official website <https://support.hdfgroup.org/HDF5/Tutor/tools.html>.
+
+The following figure shows the result visualized with the tool HDFView:
+
+![Figure 1: Results of creating groups and subgroups](pics/create_groups.png)
+
+The output for `h5dump` is:
+
+@code
+$ h5dump mytest.h5
+HDF5 "mytest.h5" {
+GROUP "/" {
+   GROUP "Group1" {
+      GROUP "SubGroup1" {
+      }
+   }
+}
+}
+@endcode
+
+[1]: https://github.com/opencv/opencv_contrib/tree/master/modules/hdf/samples/create_groups.cpp