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FAQs

FAQs

A list of GOCE User Toolbox frequently asked questions (FAQs) and answers:

Q: What is GUT?
A: GUT is a tool to facilitate the use, viewing and post-processing of GOCE Level 2 mission data products in the fields of geodesy, oceanography and solid Earth physics.

Q: What can GUT do?
A:

  • compute geoid heights at a chosen maximum degree and order over a grid or transect.
  • compute gravity anomalies, height anomalies and vertical deflections on the surface of the terrain for a range of maximum degree and order expansions over a grid or transect.
  • compute surface gravity potential, surface gravitational potential and surface gravity on the surface of the terrain for a range of maximum degree and order expansions over a grid or transect.
  • compute the spherical harmonic expansion of a gridded field and a gridded field from its spherical harmonic expansion.
  • compute the ocean's mean dynamic topography and the geostrophic velocities in direction/modulus or meridional/zonal components.
  • filter data in the spectral and spatial domains with standard anisotropic filter kernels over grid and transect.
  • transform data between different reference ellipsoid and tide-systems.
  • translate a gridded surface to a different grid by bilinear or spline interpolation.
  • adjust the geoid height in spectral domain by height correction terms.
  • removal of scalar bias from data on grid/transect.
  • manage the time-system attribute of a time-varying surface.
  • calculate data statistic on whole dataset or on a data subset.

Q: Is GUT Open Source?
A: GUT is a fully open source tool distributed under the terms of the GNU General Public License. You can download the source code by completing the GUT Registration and Licensing Form.

Q: How do I install GUT?
A: Information about how to install GUT.

Q: What are the computer requirements to use GUT?
A: The system requirements of GUT (not considering the BRAT Display) are:

  • minimum 256 MB RAM
  • 2.5 GB hard disk space

There are Binary Packages available for:

  • Windows XP, Windows Vista or Windows 7 (32 bits only)
  • Linux (GLIBC 2.3.6 and GLIBCXX 3.4.8 or later)
  • Mac OS 10.4, 10.5 or 10.6 (ppc/intel)

The supported Platforms are for the Source Package:

  • Linux/Unix (with gcc 4.1.2 or later)
  • Mac OS 10.4, 10.5 or 10.6 (ppc/intel, Developer Tools need to be installed)

Q: What data comes with GUT?
A: Along with the GUT software, you can find a collection of input datasets with:

  • An updated mean dynamic topographies (MDT) at different resolutions;
  • An updated mean sea surface models (MSS). Regional and global models are available at different resolutions;
  • The last release of GOCE data;
  • A cycle of Sea Level Anomaly;
  • An altimetry-corrected digital elevation model at global level (DEM);
  • A land-sea mask.

Q: How can I display the results in GUT?
A: The results of your processing can be displayed in GUT using the BRAT Display, included in the GUT release. Furthermore, the results can be converted in KML format and displayed by Google Earth® or converted in TIFF and displayed by commonly used graphics tools.

Finally, several third party free tools for the visualisation of netCDF data are available online. For more information, please consult Software for Manipulating or Displaying NetCDF Data page.

Q: How can I convert netCDF files in ASCII and ASCII to netCDF?
A: The NetCDF files are binary files and are therefore not viewable with regular text editors. However, the ncdump utility is available to work with the netCDF format and is part of the standard netCDF software distribution. The ncdump is a command line utility. Depending on the arguments provided it generates a text-based representation of all the netCDF data or the structure of a netCDF file , or just the data for specified variables.

The simplest invocation of the ncdump tool that will generate data in a human-readable format (ASCII [CDL]) is: ncdump input_file.nc

To view the header information only, the -h flag must be added to the command-line invocation: ncdump -h input_file.nc

For more information, see the ncdump documentation.

To do the reverse, that is, to convert an ASCII (CDL) file to the netCDF format, the command-line tool ncgen can be invoked.

For more information, see the ncgen documentation.

Consult also the unidata page to know how to install ncdump and ncgen utilities on Windows/Linux and how to download third-party converter tools.

Q: In which format can I export the results?
A: The formats in which GUT can export the results are:

  • netCDF ( CF-Convention Adopted)
  • ASCII GRAVSOFT (Only gridded format)
  • KML wrapper file (Only gridded format)
  • TIFF image file (Only gridded format)

Q: In which format can I import the results?
A: The supported input formats are:

  • L2 GOCE Data Products (EGM_GOC_2 type only)
  • netCDF (CF-Convention Adopted)
  • ASCII GRAVSOFT (Grid Format)
  • ASCII ICGEM (Spherical Harmonics Format)

Q: What kind of netCDF files is GUT able to read?
A: The netCDF files provided as input to GUT must be in CF (Climate & Forecast) compliant format (http://cf-pcmdi.llnl.gov), adopting for the data name attribute the naming convention as reported in the user guide (consult the GUT Installation Guide for more information).

Q: Is GUT compliant with the data generated from BRAT?
A: Yes, as long as the data, coming from BRAT, are CF-Convention compliant.

Q: Can I import GOCE gravity gradients in GUT?
A: No, GUT is not supporting GOCE L1b products for the time being. It may be added in a future version if there are user requests.

Q: Is there any Graphic User Interface (GUI) for GUT?
A: No, GUT does not yet have a Graphic User Interface to interact with the tool.

Q: Can I write GUT workflows by myself?
A: In order to operate, GUT uses external descriptions of the requested processing steps written in XML format and called workflows. Inside the workflows, the processing steps are stated calling the processing units. In the processing units are encapsulated the basic algorithms of GUT and they can be assembled together to form a complete processing chain (workflow) if structurally valid.

This allows customisation of data processing and extension of the capabilities of the toolkit by the user without the need to code in C++ since the definition of the workflows is external to the command line tool. The base GUT installation provides a suite of common-use workflows, but you can extend the suite by creating additional workflow files. Read the tutorial for more details.

Q: How can I customize the GUT according my purposes?
A: One can extend GUT by software development of additional processing units, using C/C++ or Fortran APIs. For more information read the GUT Installation Guide and the readme file in the src folder, in the GUT directory tree.

Q: How can I receive support in using GUT?
A: You can request for assistance by emailing gut.info@esa.int. To speed-up the support procedure, you are advised to provide the following information:

  • Explanation of the problem
    • What were you trying to achieve
    • What did you do
    • What failed
  • Input files
    • If possible provide the input files
    • or if they are publicly available, refer to their URL
  • GUT version
  • System details
    • Operating System version
    • Amount of RAM memory

Q: Where can I download GUT?
A: GUT can be downloaded by completing the GUT Registration and Licensing Form.

Q: Can I receive a copy of GUT on disk?
A: Contact the ESA Earth Observation Helpdesk.

Q: Can I be part of the GUT community?
A: GUT is an open group community; you can be part of the community and share your workflows, scripts, data and questions with the GUT team. Email gut.info@esa.int to receive more information.

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