0 Purpose

There are few online learning materials that depend on this package , So tidy this bag , Some things we can use in our work api To study

https://www.unidata.ucar.edu/

https://www.unidata.ucar.edu/software/netcdf/examples/programs/


https://docs.unidata.ucar.edu/netcdf-java/5.1/userguide/common_data_model_overview.html#data-access-layer-object-model



https://docs.unidata.ucar.edu/netcdf-java/5.1/userguide/using_netcdf_java_artifacts.html

python 

https://unidata.github.io/MetPy/latest/examples

1 Why learn this dependency

Now there are many formats of data , For example, meteorological data , Generally used nc Format file for storage , We got this file , In our project code , To parse , This nc The format file is binary stream , So you need to use professional tools to parse , This dependency is to help us resolve in our project nc Format

2 Common data model

Common Data Model It has three layers , They build on each other to add richer semantics in turn ：

1   Data access layer , Also known as the syntactic layer , Handle data reading and writing .

2   The coordinate system layer identifies the coordinates of the data array . Coordinates are a complete representation of scientific data 
 General concept ; We have also established a special geographic reference coordinate system ,
 This is very important to the earth science community .

3  Scientific Feature Types Layers identify specific types of data ,
 For example, grid 、 Radial and point data , Add special methods for each type of data .

3 Data access layer object model

3.1 Dataset

Dataset = Data sets

Data sets can be netCDF、HDF5、GRIB Wait for the documents 、OPeNDAP Data sets 、 A collection of files can be accessed through netCDF API Any other content accessed . We sometimes use the term CDM Data sets to represent any of these possibilities , And emphasize that the dataset does not have to be netCDF File format .

 The type of dataset we often use is ：
nc  Format   GRB  Format ,DAT Format 

3.2 Group

Group = Group
Group is an attribute 、 dimension 、EnumTypedef、 Containers for variables and nested groups .Dataset Medium Groups Form a hierarchical tree , Just like a directory on a disk .Dataset There is always at least one Group, That is root Group, Its name is an empty string .

3.3 Variable

Variable = Variable
Variables are containers of data . It has a data type 、 A set of dimensions that define the shape of its array , And an optional set of attributes . Any shared dimensions it uses must be in the same group or parent group .

3.4 Dimension

Dimensions are used to define the array shape of variables . It can be shared among variables , This provides a simple and powerful way to correlate variables . When sharing dimensions , It has a unique name within the Group . If there is no limit , The length of the dimension may increase . If it is variableLength, The actual length depends on the data , Only by reading the data can we find .variableLength Dimension Cannot be shared or unrestricted .

3.5 Attribute

Properties have names and values , And associate any metadata with variables or groups . The value is a scalar or one-dimensional array of strings or numbers , So the possible data types are （String、byte、short、int、long、float、double）. Integer types （byte、short、int、long） It can be signed or unsigned .

3.6 structure

A structure is a variable that contains other variables , Be similar to C Structure in or in a relational database That's ok . Usually , The data in the structure is physically tightly stored on disk , Therefore, all the data in the structure can be retrieved efficiently at the same time . The variables contained in the structure are member variables , Can only be read in the context of its containing structure .

3.7 Sequence

A sequence is a one-dimensional structure , Its length is unknown before you actually read the data . To access data in a sequence , You can only traverse the sequence , Get data from one structure instance at a time .

3.8 EnumTypedef

EnumTypedef Is an enumeration of strings , from enum Type variables use .

3.9 Array

The array contains the actual data after reading variables from disk or network . You can call read() Or its variant to get an array from a variable . The array is rectangular （ Such as Fortran Array ）. Every DataType There's a special Array type .

4 Coordinate system object model

4.1 Variable

** A variable can have zero or more coordinate systems , It contains one or more axes .** If CoordinateAxis The dimension set of is a subset of the dimension set of variables , be CoordinateAxis Can only be variable CoordinateSystem Part of . This ensures that each data point in the variable is for CoordinateSystem Each of the CoordinateAxis Have a corresponding coordinate value .

5 api Study

5.1 open nc file open（）

        String filename = "E:\\ Grid point \\nc\\66.nc";
        NetcdfFile ncfile = null;
        try {
    
            ncfile = NetcdfFile.open(filename);
            //  Console output 
            System.out.println(ncfile);

        } catch (IOException ioe) {
    
            System.out.println("trying to open " + filename+ioe);
        } finally {
    
            if (null != ncfile) try {
    
                ncfile.close();
            } catch (IOException ioe) {
    
                System.out.println("trying to open " + filename+ioe);
            }
        }

5.2 findVariable（）

According to the specific variable name , Get the specific attributes in the current variable

private static void process(NetcdfFile ncfile){
    
        String varName = "hyai";
        Variable v = ncfile.findVariable(varName);
        if (null == v) return;
        try {
    
            System.out.println(v);
        } finally {
    

        }
    }

5.3

6 Import dependence

This dependency is added to our project , It is equivalent to adding this parsing nc Documentation software

        <dependency>
            <groupId>edu.ucar</groupId>
            <artifactId>netcdfAll</artifactId>
            <version>5.1.0</version>
        </dependency>

7 open nc file

We have a nc file

It means according to the code , Read the contents of this binary file , Let's take a look at what the code reads . Output the read thing to the console , And read TXT file ,

        String filename = "E:\\ Grid point \\nc\\66.nc";
        NetcdfFile ncfile = null;
        try {
    
            ncfile = NetcdfFile.open(filename);
            //  Console output 
            System.out.println(ncfile);

        } catch (IOException ioe) {
    
            System.out.println("trying to open " + filename+ioe);
        } finally {
    
            if (null != ncfile) try {
    
                ncfile.close();
            } catch (IOException ioe) {
    
                System.out.println("trying to open " + filename+ioe);
            }
        }

The output is

You can find , The output is to use panoply Software open nc file ;