NCL-NCAR Comman Language Overview
Translated and Interpreted by Cheng An (承安)
翻译及阐述：承安
NCL是一种在气象及气候领域，为科学数据处理及数据可视化设计的高级语言。
以下是根据ncl官方网站 NCL Overview上的英文资料进行相应翻译得到，供自己学习只用。如果他人想要拷贝、传播，请随意使用；但请注明是由承安（Cheng An）翻译并首发于。
(The NCAR Command Language (NCL), a product of the Computational & Information Systems Laboratory at the National Center for Atmospheric Research (NCAR) and sponsored by the National Science Foundation, is a free interpreted language designed specifically for scientific data processing and visualization.
NCL是由美国国家大气研究中心（NCAR）的计算及信息系统实验室的产品，并且得到了美国国家科学基金会（NSF）的资助。NCL是一款专为科学数据处理及图形化设计的免费的解释语言。
NCL has robust file input and output. It can read and write netCDF-3, netCDF-4 classic, netCDF-4, HDF4, binary, and ASCII data. It can read HDF-EOS2, HDF-EOS5, GRIB1, GRIB2, and OGR files (shapefiles, MapInfo, GMT, Tiger). It can be built as an OPeNDAP client.
NCL能够实现稳健的文件输入和输出。
它能够读/写的数据类型包括netCDF-3, netCDF-4 classic, netCDF-4, HDF4, binary, and ASCII data.
NCL能够读取的数据包括HDF-EOS2, HDF-EOS5, GRIB1, GRIB2, and OGR files (shapefiles, MapInfo, GMT, Tiger).
而且NCL也可以编译成OPeNDAP客户端。
NCL visualizations are world class and highly customizable.
NCL的图形化效果可谓是世界一流的，而且具有高度定制化的特点。
Both NCL and NCAR Graphics are released as one package in source code or pre-compiled binary format. See the download page for more information. NCAR Graphics still has its own home page.
NCL和NCAR Graphics会以源代码或者预编辑二进制格式，合并发布在同一个包（package）。
The NCL User Guide is an excellent beginner's guide to NCL language basics, with a step-by-step tutorial on writing NCL scripts for reading/writing files, doing computational analyses, and generating publication-quality graphics.
NCL User Guide，NCL用户指南非常适合初学者学习NCL语言基础知识。指南里包含了一步一步指导初学者编写NCL脚本实现读/写文件，计算分析，以及生成发表物级别质量的图表。
The software comes with useful command line tools:
- ncl_filedump - prints the contents of supported files (netCDF, HDF4/5, GRIB1, GRIB2, HDF-EOS2/5, and shapefile, and CCM History Tape)
- ncl_convert2nc - converts one or more GRIB1, GRIB2, HDF4/5, HDF-EOS2/5, or shapefile files to netCDF formatted files.
- WRAPIT - allows you to wrap Fortran 77/90 routines and call them from ncl.
软件自带有用的命令行工具：
- ncl_filedump - prints the contents of supported files (netCDF, HDF4/5, GRIB1, GRIB2, HDF-EOS2/5, and shapefile, and CCM History Tape)
- ncl_convert2nc - converts one or more GRIB1, GRIB2, HDF4/5, HDF-EOS2/5, or shapefile files to netCDF formatted files.
- WRAPIT - allows you to wrap Fortran 77/90 routines and call them from ncl.
NCL and NCAR Graphics run on UNIX-based operating systems, including Linux, MacOSX, and Cygwin/X running on Windows. See this document on running NCL in the NCAR Cheyenne environment.
NCL can be run in interactive mode, where each line is interpreted as it is entered at your workstation, or it can be run in batch mode as an interpreter of complete scripts. You can also use command line options to set options or variables on the NCL command line.
The power and utility of the language are evident in three main components:
- file input and output
- data analysis
- visualization
NCL has many features common to modern programming languages, including types, variables, operators, expressions, conditional statements, loops, and functions and procedures.
In addition to common programming features, NCL also has features that are not found in other programming languages, including features that handle the manipulation of metadata, the configuration of the visualizations, the import of data from a variety of data formats, and an algebra that supports array operations.
NCL comes with many useful built-in functions and procedures for processing and manipulating data. There are over 600 functions and procedures that include routines for:
- use specifically with climate and model data
- computing empirical orthogonal functions, Fourier coefficients, singular value decomposition, averages, standard deviations, sin, cosine, log, min, max, etc.
- retrieving and converting date information
- drawing primitives (lines, filled areas, and markers), wind barbs, weather map symbols, isosurfaces, and other graphical objects
- robust file handling
- 1-dimensional, 2-dimensional, and 3-dimensional interpolation, approximation, and regridding
- facilitating computer analysis of scalar and vector global geophysical quantities (most are based on the package known as Spherepack)
- retrieving environment variables and executing system commands
NCL supports calling C and Fortran external routines, which makes NCL infinitely configurable.
NCL uses several other publicly-available software packages and databases for some of its file I/O, data analyses routines, and high-resolution coastlines. These software packages include:
- cairo - a 2D graphics library with support for multiple output devices. It is used in NCL to provide PNG, PS, and PDF output.
- DCDFLIB - cumulative distribution functions, inverses, and parameters for beta, binomial, chi-square, noncentral chi-square, F, noncentral F, gamma, negative binomial, normal, Poisson, Student's t. Developed by Barry W. Brown, James Lovato, Kathy [email protected]/[email protected]
- FFTPACK5 - a Fortran subroutine library of Fast Fourier Transforms (FFT's) developed at the National Center for Atmospheric Research.
- g2clib - this library contains "C" decoder/encoder routines for GRIB edition 2.
- GDAL - Geospatial Data Abstraction Library
- GRIBEX - GRIB encoding/decoding software.
- HDF 4 - a file format for storing scientific data and a software library that provides high-level APIs and a low-level data interface.
- HDF 5 - a general purpose library and file format for storing scientific data. HDF5 addresses some of the deficiencies of HDF 4.
- HDF-EOS2 and HDF-EOS5 - software libraries built on top of HDF4 and HDF5 to support EOS-specific data structures, namely Grid, Point, and Swath.
- JasPer - an open-source initiative to provide a free software-based reference implementation of the codec specified in the JPEG-2000 Part-1 standard (i.e., ISO/IEC 15444-1). This project was started as a collaborative effort between Image Power, Inc. and the University of British Columbia.
- LAPACK - a library of Fortran 77 subroutines for solving the most commonly occurring problems in numerical linear algebra.
Copyright (c) 1992-2007. The University of Tennessee. All rights reserved.- netCDF - a machine-independent format for representing scientific data (also, an interface for array-oriented data access and a library that provides an implementation of the interface).
- Ngmath - a collection of mathematical procedures for which there are equivalent Fortran, C, and NCL entries.
- OPeNDAP - a framework that simplifies all aspects of scientific data networking.
- PROJ.4 - Cartographic Projections Library
- RANGS (Regionally Accessible Nested Global Shorelines) - a multi-resolution coastline database developed by Rainer Feistel from Wessel and Smith's GSHHS (Global Self-consistent Hierarchical High-resolution Shoreline) database.
- Spherepack - a collection of Fortran programs that facilitates computer modeling of geophysical processes.
- SZIP - provides lossless compression of scientific data; is provided with HDF software products as of HDF5 Release 1.6.0 and HDF4 Release 2.0.
- Triangle - a two-dimensional quality mesh generator and delaunay triangulator, used in NCL's contouring package for non-uniform grids.
- UDUNITS-2 - a C/Fortran library that supports conversion of unit specifications between formatted and binary forms, arithmetic manipulation of unit specifications, and conversion of values between compatible scales of measurement. NCL uses it in particular for converting UTC-referenced time.
- UDUNITS-2 extensions - David Pierce of UCSD wrote some extensions to the "utCalendar" and "utInvCalendar" routines as part of ncview, and gave us permission to include them in NCL.
- UTM to lat/lon (and vice versa) converters - a set of routines written by Peter Daly of MIT Ocean Acoustics that convert UTM to Lat/Longitude and vice-versa, using the WGS-84 (GPS standard) or Clarke 1866 Datums.
- Vis5d+ - a free OpenGL-based volumetric visualization program for scientific datasets in 3+ dimensions.
- zlib - a Massively Spiffy Yet Delicately Unobtrusive Compression Library.
How to cite NCL
Please cite NCL in your publications using the following DOI citation (line breaks were added for clarification but the citation should be on one line):
The NCAR Command Language (Version 6.4.0) [Software]. (2017).
Boulder, Colorado: UCAR/NCAR/CISL/VETS. http://dx.doi.org/10.5065/D6WD3XH5
Update the NCL version and year as appropriate.
For more information about DOIs, see http://www.doi.org and http://en.wikipedia.org/wiki/Digital_object_identifier.