DOCSLIB.ORG

Working with a Netcdf File in Arcgis

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Working with a Netcdf File in Arcgis Learning to Work with Temporal Data in ArcGIS Working with a netCDF File in ArcGIS Objective NetCDF (network Common Data Form) is a file format for storing multidimensional scientific data (variables) such as temperature, humidity, pressure, wind speed and direction. Each of these variables can be displayed through a dimension (such as time) in ArcGIS by making a layer or table view from the netCDF file. In this tutorial, you’ll learn how to create a netCDF raster and a table and how to display a specific time step. You will also create a temperature profile at a location and finally perform some analysis with netCDF raster layers. Locating data and map documents • Data folder: TDinArcGIS\Exercise2\Data • NetCDF file: temperature.nc, Variable: tmin (winter minimum temperature) • Map documents: NetCDFinArcGIS.mxd • Toolbox: AnalysisWithNetCDF.tbx A: Making a netCDF raster layer In this exercise, you’ll create a netCDF raster layer using the variable tmin. You will change the display by selecting a different time step. A1: Opening an existing map document 1. Start ArcMap by using the Programs list on your Start menu. 2. If the ArcMap startup dialog box appears, check An existing map, then double‐click Browse for maps. If you previously checked Do not show this dialog again on the ArcMap startup dialog box, open the map document by clicking Open instead. 3. Navigate to the TDinArcGIS\Exercise2\Data folder on your local drive, click NetCDFinArcGIS.mxd, then click Open. Nothing is displayed but it is not empty. A table and a graph are saved in the document for exercises B and C. A2: Making a netCDF raster layer 1. In the ArcToolbox window, expand the Multidimension Tools toolbox. 2. Right‐click Make NetCDF Raster Layer and click Open or double‐click the tool. 3. Type the name in the Input netCDF File, or alternatively, click the browse button to navigate to the input file temperature.nc in TDinArcGIS\Exercise2\Data. ESRI ‐ 1 4. Click Variable, click the Variable drop‐down arrow, and select a tmin from the list. 5. Click X Dimension, click the X Dimension drop‐down arrow, and select lon from the list. 6. Click Y Dimension, click the Y Dimension drop‐down arrow, and select a lat from the list. 7. Type tmin_Layer in the Output Raster Layer. 8. Click OK. A netCDF raster layer is added to the table of contents (ToC) displaying the winter minimum temperature of 1875 from the default (first) time slice. Note that the minimum and maximum temperatures are ‐59.0669 and 27.6854 respectively. A3: Displaying a specific time slice You can display a different slice of a netCDF raster layer, feature layer, or table by changing dimension values on the netCDF property dialog box. 1. Right‐click the netCDF raster layer tmin_Layer in the table of contents and click Properties. 2. Click the NetCDF tab. ESRI ‐ 2 3. Click the value field next to the dimension year. A drop‐down arrow will appear. 4. Click the drop‐down arrow and click 1/1/1940. 5. Click OK on the Layer Properties dialog box. The netCDF raster layer tmin_Layer is now displaying the winter minimum temperature of 1940. Note that the minimum and maximum temperatures have changed to ‐60.2398 and 28.153 respectively. A4: Returning to the default time slice You can return to the default time slice by changing the dimension on the layer property dialog or you can use the Select By Dimension tool. 1. Right‐click Select by Dimension and click Open or double‐click the tool. 2. Click Input Layer or Table drop‐down arrow and select tmin_Layer from the list. 3. Click OK. ESRI ‐ 3 The netCDF raster layer tmin_Layer is now displaying the default time step i.e. the winter minimum temperature of 1875. Note that the minimum and maximum temperatures are now back to ‐59.0669 and 27.6854 respectively. B: Creating a profile at a location In this exercise you will create a temperature profile at a location. You’ll first create a netCDF table with predicted temperature values. A graph is already created for you. You will examine the graph and its properties. B1: Making a netCDF table view 1. Right‐click Make NetCDF Table View and click open or double‐click the tool. 2. Type the name in the Input netCDF File, or alternatively, click the browse button to navigate to the input file temperature.nc in TDinArcGIS\Exercise2\Data. 3. Click Variables, click the Variables drop‐down arrow, and select tmin from the list. 4. Type temperature_View in the Output Table View. 5. Click Row Dimensions, click the Row Dimensions drop‐down arrow, and select year from the list. ESRI ‐ 4 6. Click Dimension Values, click the Dimension Values drop‐down arrow, and select lon from the list. The dimension will be added to the table. Click the Value drop‐down arrow next to the added dimension and type in ‐111.75. 7. Click Dimension Values, click the Dimension Values drop‐down arrow, and select lat from the list. The dimension will be added to the table. Click the Value drop‐down arrow next to the added dimension and type in 45.75. 8. Click OK. 9. Click on the Source tab in the table of contents. 10. Right‐click the netCDF table view temperature_View in the table of contents and click Open. Examine the fields and values in the Attributes of temperature_View. In the next step you will display a graph created from a netCDF table view similar to the one you just created. ESRI ‐ 5 B2: Displaying a graph created from a netCDF table 1. Click Tools on the Main Menu, point to Graphs, then click Minimum Winter Temperature. The graph displays the predicted change in minimum winter temperature from 1875 to 2095 at longitude = ‐111.75 and latitude = 45.75. 2. Right‐click anywhere on the graph, then click properties. Examine graph properties such as Graph type, X field, Y field ctc. 3. Click OK after you are done. ESRI ‐ 6 The graph shows a significant increase (shift) between years 1935 and 1940. In the next exercise we will create a temperature difference raster between these two time slices. 4. Close the graph by clicking the cross at upper right corner. 5. Close the table Attribute of temperature_View. 6. Click on the Display tab in the table of contents. C: Finding difference between time slices The graph shows a significant increase (shift) between years 1935 and 1940. In this exercise you’ll create a temperature difference raster between these two time slices by using a model. 1. Find and expand the AnalysisWithNetCDF toolbox in ArcToolbox. 2. Right‐click the model FindingDifference, then click Edit. 3. Examine the model. Double‐click on Make NetCDF Raster Layer process and examine parameters. Note that Dimension Values parameter is used to create a raster for a specific time step. 4. Run the model by clicking the run button. Raster layer tmin_diff will be added to the table of contents. ESRI ‐ 7 Move or minimize the model so that you can see the tmin_diff layer in the display. 5. Double‐click on the legend of tmin_diff and select a suitable color ramp from the dropdown list. 6. Click OK. The differences of temperature between two time steps are significant and vary across the area of interest. Two shifts on the graph also suggest some discrepancies in the time‐series. We now need to go back and check the original (simulated monthly temperature) data and how we processed the data to derive this average minimum winter temperature. ESRI ‐ 8 .
Load more

Recommended publications
  • A New Data Model, Programming Interface, and Format Using HDF5
    NetCDF-4: A New Data Model, Programming Interface, and Format Using HDF5 Russ Rew, Ed Hartnett, John Caron UCAR Unidata Program Center Mike Folk, Robert McGrath, Quincey Kozial NCSA and The HDF Group, Inc. Final Project Review, August 9, 2005 THG, Inc. 1 Motivation: Why is this area of work important? While the commercial world has standardized on the relational data model and SQL, no single standard or tool has critical mass in the scientific community. There are many parallel and competing efforts to build these tool suites – at least one per discipline. Data interchange outside each group is problematic. In the next decade, as data interchange among scientific disciplines becomes increasingly important, a common HDF-like format and package for all the sciences will likely emerge. Jim Gray, Distinguished “Scientific Data Management in the Coming Decade,” Jim Gray, David Engineer at T. Liu, Maria A. Nieto-Santisteban, Alexander S. Szalay, Gerd Heber, Microsoft, David DeWitt, Cyberinfrastructure Technology Watch Quarterly, 1998 Turing Award Volume 1, Number 2, February 2005 winner 2 Preservation of scientific data … the ephemeral nature of both data formats and storage media threatens our very ability to maintain scientific, legal, and cultural continuity, not on the scale of centuries, but considering the unrelenting pace of technological change, from one decade to the next. … And that's true not just for the obvious items like images, documents, and audio files, but also for scientific images, … and MacKenzie Smith, simulations. In the scientific research community, Associate Director standards are emerging here and there—HDF for Technology at (Hierarchical Data Format), NetCDF (network the MIT Libraries, Common Data Form), FITS (Flexible Image Project director at Transport System)—but much work remains to be MIT for DSpace, a groundbreaking done to define a common cyberinfrastructure.
    [Show full text]
  • Using Netcdf and HDF in Arcgis
    Using netCDF and HDF in ArcGIS Nawajish Noman Dan Zimble Kevin Sigwart Outline • NetCDF and HDF in ArcGIS • Visualization and Analysis • Sharing • Customization using Python • Demo • Future Directions Scientific Data and Esri • Direct support - NetCDF and HDF • OPeNDAP/THREDDS – a framework for scientific data networking, integrated use by our customers • Users of Esri technology • National Climate Data Center • National Weather Service • National Center for Atmospheric Research • U. S. Navy (NAVO) • Air Force Weather • USGS • Australian Navy • Australian Bur.of Met. • UK Met Office NetCDF Support in ArcGIS • ArcGIS reads/writes netCDF since version 9.2 • An array based data structure for storing multidimensional data. T • N-dimensional coordinates systems • X, Y, Z, time, and other dimensions Z Y • Variables – support for multiple variables X • Temperature, humidity, pressure, salinity, etc • Geometry – implicit or explicit • Regular grid (implicit) • Irregular grid • Points Gridded Data Regular Grid Irregular Grid Reading netCDF data in ArcGIS • NetCDF data is accessed as • Raster • Feature • Table • Direct read • Exports GIS data to netCDF CF Convention Climate and Forecast (CF) Convention http://cf-pcmdi.llnl.gov/ Initially developed for • Climate and forecast data • Atmosphere, surface and ocean model-generated data • Also for observational datasets • The CF conventions generalize and extend the COARDS (Cooperative Ocean/Atmosphere Research Data Service) convention. • CF is now the most widely used conventions for geospatial netCDF data. It has the best coordinate system handling. NetCDF and Coordinate Systems • Geographic Coordinate Systems (GCS) • X dimension units: degrees_east • Y dimension units: degrees_north • Projected Coordinate Systems (PCS) • X dimension standard_name: projection_x_coordinate • Y dimension standard_name: projection_y_coordinate • Variable has a grid_mapping attribute.
    [Show full text]
  • A COMMON DATA MODEL APPROACH to NETCDF and GRIB DATA HARMONISATION Alessandro Amici, B-Open, Rome @Alexamici
    A COMMON DATA MODEL APPROACH TO NETCDF AND GRIB DATA HARMONISATION Alessandro Amici, B-Open, Rome @alexamici - http://bopen.eu Workshop on developing Python frameworks for earth system sciences, 2017-11-28, ECMWF, Reading. alexamici / talks MOTIVATION: FORECAST DATA AND TOOLS ECMWF Weather forecasts, re-analyses, satellite and in- situ observations N-dimensional gridded data in GRIB Archive: Meteorological Archival and Retrieval System (MARS) A lot of tools: Metview, Magics, ecCodes... alexamici / talks MOTIVATION: CLIMATE DATA Copernicus Climate Change Service (C3S / ECMWF) Re-analyses, seasonal forecasts, climate projections, satellite and in-situ observations N-dimensional gridded data in many dialects of NetCDF and GRIB Archive: Climate Data Store (CDS) alexamici / talks HARMONISATION STRATEGIC CHOICES Metview Python Framework and CDS Toolbox projects Python 3 programming language scientic ecosystems xarray data structures NetCDF data model: variables and coordinates support for arbitrary metadata CF Conventions support on IO label-matching broadcast rules on coordinates parallelized and out-of-core computations with dask alexamici / talks ECMWF NETCDF DIALECT >>> import xarray as xr >>> ta_era5 = xr.open_dataset('ERA5-t-2016-06.nc', chunks={}).t >>> ta_era5 <xarray.DataArray 't' (time: 60, level: 3, latitude: 241, longitude: 480)> dask.array<open_dataset-..., shape=(60, 3, 241, 480), dtype=float64, chunksize=(60, 3, Coordinates: * longitude (longitude) float32 0.0 0.75 1.5 2.25 3.0 3.75 4.5 5.25 6.0 ... * latitude (latitude) float32 90.0 89.25 88.5 87.75 87.0 86.25 85.5 ... * level (level) int32 250 500 850 * time (time) datetime64[ns] 2017-06-01 2017-06-01T12:00:00 ..
    [Show full text]
  • MATLAB Tutorial - Input and Output (I/O)
    MATLAB Tutorial - Input and Output (I/O) Mathieu Dever NOTE: at any point, typing help functionname in the Command window will give you a description and examples for the specified function 1 Importing data There are many different ways to import data into MATLAB, mostly depending on the format of the datafile. Below are a few tips on how to import the most common data formats into MATLAB. • MATLAB format (*.mat files) This is the easiest to import, as it is already in MATLAB format. The function load(filename) will do the trick. • ASCII format (*.txt, *.csv, etc.) An easy strategy is to use MATLAB's GUI for data import. To do that, right-click on the datafile in the "Current Folder" window in MATLAB and select "Import data ...". The GUI gives you a chance to select the appropriate delimiter (space, tab, comma, etc.), the range of data you want to extract, how to deal with missing values, etc. Once you selected the appropriate options, you can either import the data, or you can generate a script that imports the data. This is very useful in showing the low-level code that takes care of reading the data. You will notice that the textscan is the key function that reads the data into MATLAB. Higher-level functions exist for the different datatype: csvread, xlsread, etc. As a rule of thumb, it is preferable to use lower-level function are they are "simpler" to understand (i.e., no bells and whistles). \Black-box" functions are dangerous! • NetCDF format (*.nc, *.cdf) MATLAB comes with a netcdf library that includes all the functions necessary to read netcdf files.
    [Show full text]
  • R Programming for Climate Data Analysis and Visualization: Computing and Plotting for NOAA Data Applications
    Citation of this work: Shen, S.S.P., 2017: R Programming for Climate Data Analysis and Visualization: Computing and plotting for NOAA data applications. The first revised edition. San Diego State University, San Diego, USA, 152pp. R Programming for Climate Data Analysis and Visualization: Computing and plotting for NOAA data applications SAMUEL S.P. SHEN Samuel S.P. Shen San Diego State University, and Scripps Institution of Oceanography, University of California, San Diego USA Contents Preface page vi Acknowledgements viii 1 Basics of R Programming 1 1.1 Download and install R and R-Studio 1 1.2 R Tutorial 2 1.2.1 R as a smart calculator 3 1.2.2 Define a sequence in R 4 1.2.3 Define a function in R 5 1.2.4 Plot with R 5 1.2.5 Symbolic calculations by R 6 1.2.6 Vectors and matrices 7 1.2.7 Simple statistics by R 10 1.3 Online Tutorials 12 1.3.1 Youtube tutorial: for true beginners 12 1.3.2 Youtube tutorial: for some basic statistical summaries 12 1.3.3 Youtube tutorial: Input data by reading a csv file into R 12 References 14 Exercises 14 2 R Analysis of Incomplete Climate Data 17 2.1 The missing data problem 17 2.2 Read NOAAGlobalTemp and form the space-time data matrix 19 2.2.1 Read the downloaded data 19 2.2.2 Plot the temperature data map of a given month 20 2.2.3 Extract the data for a specified region 22 2.2.4 Extract data from only one grid box 23 2.3 Spatial averages and their trends 23 2.3.1 Compute and plot the global area-weighted average of monthly data 23 2.3.2 Percent coverage of the NOAAGlobalTemp 24 2.3.3 Difference from the
    [Show full text]
  • 4.04 Netcdf.Pptx
    Network Common Data Form NetCDF An Indroduction NetCDF is a set of software libraries and self- describing, machine-independent data formats that support the creation, access, and sharing of array-oriented scientific data. 1 The Purpose of NetCDF ● The purpose of the Network Common Data Form (netCDF) interface is to allow you to create, access, and share array- oriented data in a form that is self-describing and portable. ● Self-describing means that a dataset includes information defining the data it contains. ● Portable means that the data in a dataset is represented in a form that can be accessed by computers with different ways of storing integers, characters, and floating-point numbers. ● The netCDF software includes C, Fortran 77, Fortran 90, and C++ interfaces for accessing netCDF data. ● These libraries are available for many common computing platforms. 2 NETCDF Features ● Self-Describing: A netCDF file may include metadata as well as data: names of variables, data locations in time and space, units of measure, and other useful information. ● Portable: Data written on one platform can be read on other platforms. ● Direct-access: A small subset of a large dataset may be accessed efficiently, without first reading through all the preceding data. ● Appendable: Data may be efficiently appended to a netCDF file without copying the dataset or redefining its structure. ● Networkable: The netCDF library provides client access to structured data on remote servers through OPeNDAP protocols. ● Extensible: Adding new dimensions, variables, or attributes to netCDF files does not require changes to existing programs that read the files. ● Sharable: One writer and multiple readers may simultaneously access the same netCDF file.
    [Show full text]
  • Parallel Netcdf
    COMP 705: Advanced Parallel Computing HW 6: Accessing XSEDE resources; parallel NetCDF Mary Thomas Department of Computer Science Computational Science Research Center (CSRC) San Diego State University (SDSU) Due: 11/01/17 Updated: 11/06/17 COMP 705: HW 6 Due: 11/01/17 Updated: 11/06/17 2/13 Mary Thomas Table of Contents 1 Problem 6a: Accessing comet.sdsc.edu 2 Problem 6b: Using Parallel NetCDF Data Storage 3 General Instructions for all Problems Configuring the Problem Size and Processor Distribution Analysis Use TAU to Analyze Code Performance Matlab code to read NetCDF Data COMP 705: HW 6 Due: 11/01/17 Updated: 11/06/17 3/13 Mary Thomas Problem 6a: Accessing comet.sdsc.edu Problem 6a: Accessing comet.sdsc.edu Use your parallel MPI I/O (or NetCDf) code to show you can access and run jobs on comet. This includes: Logging on Setting your environment Running batch script jobs COMP 705: HW 6 Due: 11/01/17 Updated: 11/06/17 4/13 Mary Thomas Problem 6b: Using Parallel NetCDF Data Storage Problem 6b: Using Parallel NetCDF Data Storage Note: this problem is no longer required for HW4 (running on tuckoo) Modify your code to save temperature data at different time slices into a single NetCDF file You will need to define your own meta data and arrays to store. Examples include: data stored in structs, temperature, time data create names for data, and scalings (min/max temp, min/max temperature, etc.) Visualize 3 or more timeslices using software that can read your netCDF file.
    [Show full text]
  • They Have Very Good Docs At
    Intro to the Julia programming language Brendan O’Connor CMU, Dec 2013 They have very good docs at: http://julialang.org/ I’m borrowing some slides from: http://julialang.org/blog/2013/03/julia-tutorial-MIT/ 1 Tuesday, December 17, 13 Julia • A relatively new, open-source numeric programming language that’s both convenient and fast • Version 0.2. Still in flux, especially libraries. But the basics are very usable. • Lots of development momentum 2 Tuesday, December 17, 13 Why Julia? Dynamic languages are extremely popular for numerical work: ‣ Matlab, R, NumPy/SciPy, Mathematica, etc. ‣ very simple to learn and easy to do research in However, all have a “split language” approach: ‣ high-level dynamic language for scripting low-level operations ‣ C/C++/Fortran for implementing fast low-level operations Libraries in C — no productivity boost for library writers Forces vectorization — sometimes a scalar loop is just better slide from ?? 2012 3 Bezanson, Karpinski, Shah, Edelman Tuesday, December 17, 13 “Gang of Forty” Matlab Maple Mathematica SciPy SciLab IDL R Octave S-PLUS SAS J APL Maxima Mathcad Axiom Sage Lush Ch LabView O-Matrix PV-WAVE Igor Pro OriginLab FreeMat Yorick GAUSS MuPad Genius SciRuby Ox Stata JLab Magma Euler Rlab Speakeasy GDL Nickle gretl ana Torch7 slide from March 2013 4 Bezanson, Karpinski, Shah, Edelman Tuesday, December 17, 13 Numeric programming environments Core properties Dynamic Fast? and math-y? C/C++/ Fortran/Java − + Matlab + − Num/SciPy + − R + − Older table: http://brenocon.com/blog/2009/02/comparison-of-data-analysis-packages-r-matlab-scipy-excel-sas-spss-stata/ Tuesday, December 17, 13 - Dynamic vs Fast: the usual tradeof - PL quality: more subjective.
    [Show full text]
  • Introduction to Using the Netcdf Data Format with Fortran 90 I. Introduction
    Introduction to using the netCDF data format with Fortran 90 Michael Thorne ([email protected]) Last Updated: July 20, 2010 I. Introduction NetCDF – Network Common Data Form NetCDF is an array based data structure for storing multidimensional data. A netCDF file is written with an ASCII header and stores the data in a binary format. The space saved by writing binary files is an obvious advantage, particularly because one does not need worry about the byte order. Any byte- swapping is automatically handled by the netCDF libraries and a netCDF binary file can thus be read on any platform. Some features associated with using the netCDF data format are as follows: Coordinate systems: support for N-dimensional coordinate systems. • X-coordinate (e.g., lat) • Y-coordinate (e.g., lon) • Z-coordinate (e.g., elevation) • Time dimension • Other dimensions Variables: Support for multiple variables. • E.g., S-wave velocity, P-wave velocity, density, stress components… Geometry: Support for a variety of grid types (implicit or explicit). • Regular grid (implicit) • Irregular grid • Points Self-Describing: Dataset can include information defining the data it contains. • Units (e.g., km, m/sec, gm/cm3,…) • Comments (e.g., titles, conventions used, names of variables (e.g., P-wave velocity), names of coordinates (e.g., km/sec),... Full documentation on the data format can be found at: • http://www.unidata.ucar.edu/software/netcdf/ - netCDF webpage • http://www.unidata.ucar.edu/software/netcdf/docs/ - Full netCDF documentation • http://www.unidata.ucar.edu/software/netcdf/docs/netcdf-f90/ - F90 Interface guide Naming convention: NetCDF files are generally named with the .nc extension.
    [Show full text]
  • Netcdf User's Guide for Fortran 90
    NetCDF User’s Guide for Fortran 90 An Access Interface for Self-Describing, Portable Data Version 3.5 March 2002 Russ Rew, Unidata Program Center, and Robert Pincus, NOAA/CIRES Climate Diagnostics Center Copyright © 2002 University Corporation for Atmospheric Research, Boulder, Colorado. Permission is granted to make and distribute verbatim copies of this manual provided that the copyright notice and these paragraphs are preserved on all copies. The software and any accompa- nying written materials are provided “as is” without warranty of any kind. UCAR expressly dis- claims all warranties of any kind, either expressed or implied, including but not limited to the implied warranties of merchantability and fitness for a particular purpose. The Unidata Program Center is managed by the University Corporation for Atmospheric Research and sponsored by the National Science Foundation. Any opinions, findings, conclu- sions, or recommendations expressed in this publication are those of the author(s) and do not nec- essarily reflect the views of the National Science Foundation. Mention of any commercial company or product in this document does not constitute an endorse- ment by the Unidata Program Center. Unidata does not authorize any use of information from this publication for advertising or publicity purposes. Chapter : i NetCDF User’s Guide for Fortran 90 1 Introduction . 1 1.1 The NetCDF Interface . 1 1.2 NetCDF Is Not a Database Management System . 1 1.3 File Format . 2 1.4 What about Performance? . 2 1.5 Is NetCDF a Good Archive Format? . 3 1.6 Creating Self-Describing Data conforming to Conventions . 3 1.7 Background and Evolution of the NetCDF Interface .
    [Show full text]
  • Efficient Netcdf Processing for Big Datasets Singh, R.M., Yu
    22nd International Congress on Modelling and Simulation, Hobart, Tasmania, Australia, 3 to 8 December 2017 mssanz.org.au/modsim2017 Efficient NetCDF processing for big datasets R.M. Singh a, J. Yu a and G. Podger a a CSIRO Land and Water Flagship, GPO Box 1666, Canberra ACT 2601 Email: [email protected] Abstract: NetCDF (Network Common Data Form) is a data format used commonly to store scientific array- oriented data. A number of software tools exist that can be used to process and view NetCDF data. In some cases though, the existing tools cannot do the processing required and thus, we have to write code for some of the data processing operations. One such case is when we have to merge two NetCDF files. Although the core library for read-write access to NetCDF files is written in C, interfaces to the C library are available in a number of languages including Python, C#, Perl, R and others. Python with the Numpy package is widely used in scientific computing where the Numpy package provides for fast and sophisticated handling of the arrays in Python. NetCDF being an array-oriented data format, Python/Numpy combination is a good candidate for NetCDF processing. But in terms of performance, Python is not as fast as C. So if we are looping over the NetCDF data, as is the case when we merge two files, then as the dimension size of the arrays increases, so does the computing time. And if we have to merge 1000’s of such files, then we have to look for opportunities to speed up the process.
    [Show full text]
  • Parallel Netcdf: a Scientific High-Performance I/O Interface
    Parallel netCDF: A Scientific High-Performance I/O Interface Jianwei Li Wei-keng Liao Alok Choudhary ECE Department, Northwestern University jianwei, wkliao, choudhar @ece.northwestern.edu { } Robert Ross Rajeev Thakur William Gropp Rob Latham MCS Division, Argonne National Laboratory rross, thakur, gropp, robl @mcs.anl.gov { } Abstract mat and an easy-to-use application programming interface (API) for storing and retrieving netCDF files across multi- Dataset storage, exchange, and access play a critical ple platforms. More and more scientific applications choose role in scientific applications. For such purposes netCDF netCDF as their output file format. While these applica- serves as a portable and efficient file format and program- tions become computational and data intensive, they tend to ming interface, which is popular in numerous scientific ap- be parallelized on high-performance computers. Hence, it plication domains. However, the original interface does not is highly desirable to have an efficient parallel programming provide a efficient mechanism for parallel data storage and interface to the netCDF files. Unfortunately, the original de- access. sign of the netCDF interface is proving inadequate for paral- In this work, we present a new parallel interface for writ- lel applications because of its lack of a parallel access mech- ing and reading netCDF datasets. This interface is de- anism. In particular, there is no support for concurrently rived with minimal changes from the serial netCDF inter- writing to a netCDF file. Therefore, parallel applications face but defines semantics for parallel access and is tai- operating on netCDF files must serialize access. Tradition- lored for high performance. The underlying parallel I/O ally, parallel applications write to netCDF files through one is achieved through MPI-IO, allowing for dramatic perfor- of the allocated processes which easily becomes a perfor- mance gains through the use of collective I/O optimizations.
    [Show full text]