Jerry,
I am not aware of any support for vector components in reprojection.
Each component is interpolated as a scalar, so interpolated components
will be relative to the original unreprojected grid. I doubt that
direction scalars are handled correctly either. I have not looked at
this problem in detail but I suspect that it would be a substantial job.
There are no doubt others on this list who know more.
Kind regards,
Ben.
On 07/02/18 10:00, Wilwerding, Jerry wrote:
Hello,
With weather model data, the wind U and V vector components are often
represented in terms of the grid orientation instead of being based upon 'true'
north.
Does GeoServer have any support for preserving the vector representations
through projection conversions? If so, will the resulting vector components be
based upon the output projection grid or based upon 'true' north?
I am not aware of any configurations that will allow two variables (UGRD_ISBL
and VGRD_ISBL for example) to be related and transformed as directional vectors.
For example, assume a rotated latitude longitude grid (rap naïve grid). Think
of this coverage as North America and the top part of South America, rotated 90
degrees clockwise, and then shifted to the left so the pole is approximately
25% inside the right border. The winds vectors are based upon grid direction
since 'true' north varies by point as the north pole is inside the coverage
boundaries.
If I want to convert this projection into a Lambert Conformal Conic or any
other projection, it is critical to make sure the wind vectors are properly
converted. Simple interpolation as part of the conversion will not work.
I have seen some documentation regarding WMS leveraging WPS or similar
constructs in order to create wind barbs which represent speed and direction.
I believe this works well for WMS when no reprojection is requested. However,
I do not believe this same process will work with reprojections unless the
underlying wind vectors are handled correctly as part of the reprojection
process.
Insight on whether directional vectors are supported through reprojections
would be appreciated.
If it is not supported, what areas of concern exist to add this capability?
For example, is it even possible to couple two variables (U and V wind
components) under the current design or is that a major refactor?
Thanks,
Jerry
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Ben Caradoc-Davies <b...@transient.nz>
Director
Transient Software Limited <https://transient.nz/>
New Zealand
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_______________________________________________
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