[gdal-dev] Questions on working with HYCOM data in netcdf format
Stephen Woodbridge
woodbri at swoodbridge.com
Mon Jun 6 11:29:05 PDT 2016
On 6/6/2016 1:25 PM, Kurt Schwehr wrote:
> +gdal-dev
>
> Some hackish test code I had laying around from last year...
>
> https://gist.github.com/schwehr/01f6604afc7757ea0a676f0eb28be582
>
Thank you! I have it running, so next I'll play with the code.
> You might also be able to just write 80 layers of u-v, pick out pairs
> for each depth layer and have the rendering system do the
> conversion(s). You could use whatever you want once you have a
> geotiff. In this screenshot, I made an 80-layer geotiff of u and v
> alternating layers and uploaded that to Earth Engine. It's been a long
> time since I heavily used mapserver, but you could probably do the same
> there.
>
> https://www.flickr.com/photos/schwehr/26895009754/
Very cool picture!
This really helps to get me started.
Thanks,
-Steve
> On Mon, Jun 6, 2016 at 7:51 AM, Stephen Woodbridge
> <woodbri at swoodbridge.com <mailto:woodbri at swoodbridge.com>> wrote:
>
> On 6/5/2016 2:04 PM, Kurt Schwehr wrote:
>
> 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
>
>
> Hi Kurt,
>
> In the link above you mention:
>
> I've got some code written the does things like calculate the speed
> inm/s from the UV and creates a geotiff, etc
>
>
> Can you share this code, it sounds like exactly what I need for the
> current vectors? And I'm interested in figuring out how to
> read/write and work with the netcdf files.
>
> I think for now I'll work with the "u" datasets as they seem that
> they will be much easier place to start.
>
> Thanks,
> -Steve
>
>
> 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 <mailto:even.rouault at spatialys.com>
> <mailto:even.rouault at spatialys.com
> <mailto: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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