Geographical eference system of HYCOM

[Dafrosa Kataraihya]

Hello,

I am working with HYCOM flow in the GOM. I am interested in coastal u and v products at the surface level. After obtaining the dataset, they seem to have an offset Southeastward of the basemap while both of them are in WGS84 cooredinate system. 

Since I need to allign the HYCOM dataset with altimetry dataset (in WGS84), the mismatch in coordinate system makes it a bit difficult to do so. 

What do you think is the problem?

Attached screenshot explaining the same.

[Alan Wallcraft]

Which HYCOM dataset is exhibiting the offset?

Alan.

[Dafrosa Kataraihya]

It's the daily dataset from GOM reanalysis: 'HYCOM-TSIS 1/100º Gulf of Mexico Reanalysis'

https://tds.hycom.org/thredds/catalog/datasets/GOMb0.01/reanalysis/data/daily_netcdf/2016/catalog.html

specifically, 

https://ncss.hycom.org/thredds/ncss/grid/datasets/GOMb0.01/reanalysis/data/daily_netcdf/2016/gomb1_daily_2016_001_3z.nc

--

Warmest regards,

Dafrosa J. Kataraihya,

Geomatics Surveyor.

[Alan Wallcraft]

Are you assuming the grid is uniform in both longitude and latitude?

This is the native model grid, which is Mercator.  Uniform in longitude but proportional to cos(latitude) in latitude so that dx=dy in m.

Use the Latitude variable to tell your location in Latitude.  The longitude is a uniform 0.01 degree grid and using the Longitude variable may be less slightly accurate (due to round off) than using exactly 0.01 degree increments from the 1st point which is -98.0

Alan.

[Dafrosa Kataraihya]

At first I didn't specify any coordinate system.

But since you said it is the Mercator projection, what exact mercator projection is it?

I am still having issues with the alignment, not sure what I am doing wrong on my part.

[Alan Wallcraft]

It is part of the 0.01 by 0.01 degree global Mercator grid that includes the location 0E and 0N.

If you can't handle general rectilinear grids (such as defined by netCDF variables Longitude and Latitude) then you will need to experiment with your available projections to get the best fit to these variables.