[gdal-dev] Questions on working with HYCOM data in netcdf format

[Kurt Schwehr]

Stephen,

Take a look at these two discussions for starters on working with hycom:

http://gis.stackexchange.com/questions/167155/how-can-i-make-geotiffs-of-individual-depth-layers-in-the-hycom-ocean-circulatio

http://gis.stackexchange.com/questions/170882/how-can-a-make-a-netcdf-with-subgroups-smaller

You should start with the regular grids.  e.g.

ftp://ftp.hycom.org/datasets/GLBu0.08/expt_91.1/data/hindcasts/2015/hycom_glb_911_2015093000_t000_uv3z.nc

Make an 80 layer geotiff from the u/v and then use mapserver as Even
suggested.

-kurt


On Sat, Jun 4, 2016 at 6:29 AM, Even Rouault <even.rouault at spatialys.com>
wrote:

> Hi,
> >
> > I want to convert some HYCOM data into GTiff format and I'm a little
> > lost on how to get started, whether I can do what I need just using a
> > vrt or if I'm going to have to write code to process the data.
> >
> > To start with I have placed gdalinfo on one file here:
> > http://imaptools.com:8080/dl/hycom-gdalinfo.txt
> >
> > The data comes from http://hycom.org/dataserver/glb-analysis
> > and I will need to be using GLBa0.08 dataset.
> >
> > I have two use cases:
> >
> > 1) The simple one is to extract say Band 1 into a georeferenced GTiff
> > and apply color to using color ranges without loosing the NODATA. I
> > think I can do later using .vrt, correct?
>
> gdaldem color-relief can output to a VRT, but given that this netCDF file
> is
> georeferenced through a geolocation array, you'll likely have first to run
> gdalwarp -geoloc to have something useful at the end.
>
> >
> > I'm not sure how to deal with the georeferencing, because the download
> > site says: "Native hycom .[ab] data converted to NetCDF on native
> > Mercator-curvilinear HYCOM horizontal grid" but that does not seem in
> > sync with the Metadata in the file.
> >
> > 2) The more complicated case is that there are two files:
> >     a)  eastward_sea_water_velocity (aka: u, u-velocity)
> >     b)  northward_sea_water_velocity (aka: v, v-velocity)
> > that I would like to use to create a grid of vectors with arrowheads
> > using u and v to define the vector and where the color of the vector is
> > related to the magnitude of its length. Ultimately this data will get
> > rendered via mapserver so I'm wondering if I can do this via a GTiff or
> > if I will have to resort to creating a massive point shapefile with
> > attributes of angle and magnitude and use a symbol. It seems like it
> > would be best if I can keep the data as a GTiff and then sample the
> > points and render the vectors on the fly for when you zoom in/out.
>
> See
> http://mapserver.org/input/vector/vector_field.html
>
> You don't need to create a vector file.
>
> You'll have to preprocess your file to get the u and v bands in the same
> raster.
>
> Even
>
> --
> Spatialys - Geospatial professional services
> http://www.spatialys.com
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