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

Hi Randy-

> Last December you were helping us with an issue we had when displaying cross 
> sectional data from wrf. I am enclosing a screen shot of the problem. Last 
> year you wrote:
> 
> "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."
> 
> Since it is very important for us to display this data in its entirety, can 
> you elaborate on your statement above so we can think about how it might be 
> corrected.

The problem is that with the staggered native netCDF WRF grids, we have
to create a lookup between the native coords and lat/lon/alt.  This results
in a huge memory allocation which you see.  The other side effect is that
the lookup is not always accurate.

Is there a reason you don't run the WRF post processor on these grids
to convert to pressure coordinates?  That would create a great memory
savings and allow you to do the cross sections.  

Don Murray

> --- On Fri, 12/14/07, Unidata IDV Support <address@hidden> wrote:
> 
> > From: Unidata IDV Support <address@hidden>
> > Subject: [Support #YRR-987022]: Fwd: issue displaying 3D fields overlayed 
> > on terrain
> > To: address@hidden
> > Cc: address@hidden, address@hidden, address@hidden
> > Date: Friday, December 14, 2007, 3:18 PM
> > 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
> 
> 
> 
> 


Ticket Details
===================
Ticket ID: YRR-987022
Department: Support IDV
Priority: Normal
Status: Open