[Support #YRR-987022]: Fwd: issue displaying 3D fields overlayed on terrain

Hi Randy-
 
> Can IDV interpolate the staggered variables to the
> non-staggered or mass points (like w and the
> geopotential).

Yes, but it's memory intensive and not out of the box.  Whenever we do math 
or combine grids, the grids are resampled to a common domain which is 
essentially the  domain of the first grid in the equation.  So for calculating
wind speed from u and v, we resample v to the u grid and then
do the calculation (sqrt(u*u+v*v)).  The resulting grid has the 
domain of u.   There is a formula under the Grids category called
Resample Grid.  So, you could use this and take the T grid which  is
unstaggered, and resample the other grids to that, then use those
in formulas to calculate the quantities you want.  

Don

> thanks,
> randy
> 
> --- Unidata IDV Support <address@hidden>
> wrote:
> 
> > Hi Randy-
> >
> > > we have WRF output in netcdf that we are reading
> > into
> > > IDV (actually its Mcidas-V). We have been trying
> > to
> > > display the 2D terrain as a surface. Then, we want
> > to
> > > display a cross section (east-west) as a function
> > of
> > > height of let's say u-component of the wind. This
> > also
> > > works, however, the bottom few model levels are
> > > displayed "below" the terrain surface. The wrf
> > output
> > > is on a sigma level coordinate system and the
> > terrain
> > > is in meters above sealevel. We believe IDV is
> > > plotting the data wrong because it is incorrectly
> > > calculating the heights of the sigma-levels. We
> > know
> > > this because when we do an independent calculation
> > > outside of IDV the lowest layer in the model
> > matches
> > > the terrain height. You will also notice that some
> > of
> > > the data does not plot correctly east of the
> > mountains
> > > that when displayed in matlab plots correctly.
> > > I am enclosing a image of the display rotated to
> > show
> > > both the sub-terrain plotting and the missing
> > stripe
> > > of data on the right side.
> > >
> >
> > The staggered WRF grids are problematic in many ways
> > -
> > there is a lot of overhead in resampling from one
> > staggering
> > to another, it uses a lot more memory because we
> > have to
> > keep both the staggered grids and the normalized
> > grids in
> > memory, etc.  We recommend that people use the
> > WRF-Post options
> > to convert their data to pressure coordinates and
> > calculate
> > the most commonly used met variables. But we also
> > realize that
> > some need to have the staggered coordinates so we
> > allow for that.
> >
> > For variables like U which are on a vertical
> > Pressure coordinate, the height
> > is determined through a transformation of pressure
> > to height.  The default
> > is to use the standard atmophere, but you can change
> > to use a logarithmic
> > transform (Vis5D) in the Formats & Data section of
> > the User Preferences.
> >
> > The formula we use for calculating the height for
> > the variables (e.g. W) on
> > the staggered Z (height) coordinate is:
> >
> > height(x,y,z) = (PH(x,y,z)+ PHB(x,y,z)) / 9.81
> >
> >
> > So, for comparison of the first 10 values in your
> > file that are calculated vs HGT
> > we get:
> >
> > HGT:
> > 1575.897, 1580.329, 1584.752, 1590.211, 1596.429,
> > 1602.936, 1609.786,
> >   1616.844, 1624.55, 1633.135
> >
> > (W) (PH(x,y,z)+ PHB(x,y,z)) / 9.81:
> >
> > 1575.897, 1580.3292, 1584.7522, 1590.2109,
> > 1596.4291, 1602.9358, 1609.7863
> >   1616.8439, 1624.5498, 1633.1349
> >
> > (U) Pa -> m using standard atmosphere:
> >
> > 1524.0593, 1528.1156, 1532.2056, 1536.9418,
> > 1542.4225, 1548.4596, 1554.9199,
> >   1561.5878, 1568.6985, 1576.4624
> >
> > So, for the variables with a pressure vertical
> > coordinate, you will see
> > some differences.  Plotting a cross section of W
> > lines up pretty nicely
> > with the terrain.
> >
> > The blank line is a function of the sampling that we
> > have to do between
> > the native coordinates and the calculated
> > lat/lon/alt values.  I don't
> > have a good solution for that.
> >
> > Don Murray
> >
> >
> > Ticket Details
> > ===================
> > Ticket ID: YRR-987022
> > Department: Support IDV
> > Priority: Normal
> > Status: Open
> >
> >
> 
> 
> 
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Ticket Details
===================
Ticket ID: YRR-987022
Department: Support IDV
Priority: Normal
Status: Open