[IDV #COT-972342]: Loading 3D Fields in IDV

Hi Josh-

> Surface height.  Basically, I'm trying to use the height variable from the
> model to create a topography.  It works well with the NetCDF file but when I
> use the Vis5D it comes up with an unknown units error.

The problem with Vis5D files is that they usually don't contain
units which is the case in this instance.  Vis5D itself just
assumes units for certain variables (K for temp, m/sec for U and
V).  However, the IDV does need units to do computations.  It
makes no assumptions on default units because we take in files
from many disciplines and each has a different default unit
(SST in degC for example).  So, for terrain, we need a unit
compatible with m and your file has "" for the unit.

But, we do have a formula that allows you to set the unit
on your HGT field.  Select the Formulas data source
and then the Miscellaneous->Change Unit field and the
3D Surface->Topography display and click Create Display.
When the dialog pops up, put in some name for the height
(you can still use HGT if you want) and for the unitSpec
put in meter.  When you click OK, you will be prompted for
the field.  Select the HGT field from your Vis5D data source
and you'll get the display.

> I uploaded a dataset containing wind fields and the HGT field to
> http://www.meteo.psu.edu/~jmg498/test.v5d
> When I go into IDV and choose HGT -> 3D Surface -> Topography it errors out.
> But if I use the raw NetCDF and choose "Terrain Height" -> 3D Surface ->
> Topography it works.

The netCDF file has the correct units which is why it works.

Is there a way to specify the units in the WRFpost program?
The one that produces GRIB files (which also work in the
IDV) has units.

> Thanks very much for your help!

No problem.  Good luck!

Don

> On Fri, Apr 11, 2008 08:02 PM, "Unidata IDV Support"
> <address@hidden> wrote:
> >
> Hi Josh-
> >
> >> I suspect the post processing issue is the solution.  Whenever I converted
> >the
> >> data over to Vis5D format using ARWpost, the 3D fields loaded pretty
> >quickly.
> >> And you are right on with the derived parameters taking the longest amount
> >of
> >> time.  So that answers the original question.
> >
> >Okay.  That's what I figured.
> >
> >> The only issue with converting using ARWpost is IDV won't create a
> >topography
> >> from the ARW height variable once it's converted from NetCDF to Vis5D.  It
> >> comes up with an error that says something about the units being unknown.
> >I
> >> think this is an issue with Vis5D.  Do you have any suggestions on that by
> >> chance?
> >
> >When you say height, are you talking about geopotential height or
> >surface height.
> >
> >Can you provide the Vis5D file on an FTP or HTTP server for me
> >to take a look at?
> >
> >> Thanks very much!
> >
> >Have a good weekend.
> >
> >Don
> >
> >> On Fri, Apr 11, 2008 06:01 PM, "Unidata IDV Support"
> >> <address@hidden> wrote:
> >> >
> >> Hi Josh-
> >> >
> >> > Full Name: Josh Gelman
> >> > Email Address: address@hidden
> >> > Organization: PSU
> >> > Package Version:
> >> > Operating System:
> >> > Hardware:
> >> > Description of problem: Hello,
> >> >
> >> > Whenever I try to load a 3D field in IDV using a WRF ARW dataset, the
> >time
> >> >it takes to load is extremely slow (up to a half hour
> >sometimes).
> >> >For 2D fields it's nearly instantaneous.  This only seems to happen
> >with my WRF
> >> >ARW datasets.  The rest load pretty fast.  I am curious if there is
> >any way to
> >> >resolve this issue?
> >> >
> >> >When you say "only seems to happend with my WRF ARW
> >datasets", are
> >> >you
> >> >comparing them to standard (e.g. GFS) grids or WRF NMM
> >datasets?  Are
> >> >you
> >> >loading single levels or are you loading in the entire volume and
> >trying
> >> >to do cross sections or isosurfaces?
> >> >
> >> >The problem with the WRF netCDF files (NMM and ARW) is that
> >they
> >> >grids are staggered.  To handle this, we need to hold both the
> >> >native grid domain and a transform to pressure in memory.  So
> >> >at the outset, just loading in the grid is a double wammy.  Your
> >> >performance is going to depend on the size of the grid and number
> >> >of timesteps as well.  What are the dimensions of your grid?
> >> >Any of the derived parameters have an added overhead of resampling
> >> >the data from one point of the domain to another.  For example,
> >> >wind speed or wind vectors require resampling the V to the U domain.
> >> >Those are grids that I've seen really bad performance on and the
> >> >culprit is the resampling.  Straight parameters like U wind or
> >> >vapor pressure shouldn't take much longer than a standard unstaggered
> >> >high resolution NAM grid.
> >> >
> >> >In general, we suggest that users postprocess the WRF netCDF data
> >> >using WRF-POST or the Vis5D converter.  These destagger the grids
> >> >and output them on pressure levels as well as compute standard
> >> >parameters like  sea level pressure.
> >> >
> >> >There are also some steps you can take to improve performance
> >> >listed at:
> >> >
> >>
> >>http://www.unidata.ucar.edu/software/idv/docs/userguide/misc/PerformanceTuning.html
> >> >
> >> > The computers I'm running IDV on have 16 GB of memory and 3 GHz 
> >> > processor speed.
> >> >
> >> >When the data is loading slowly, is the memory monitor showing that
> >> >you are maxing out on memory?  Have you increased the default
> >> >amount of memory that the IDV gets allocated?  If not, see the
> >> >performance tips above.  Depending on your operating system, you'll
> >> >only be able to use a subset of the total memory.
> >> >
> >> > Thanks for any suggestions.
> >> >
> >> >I'm guessing that the slowdown is due to resampling which is painful
> >> >for the staggered grids.  But if you are seeing really slow loading
> >> >on one of the main fields in the grid, then there is some other
> >> >issue.
> >> >
> >> >Don Murray
> >> >
> >> >Ticket Details
> >> >===================
> >> >Ticket ID: COT-972342
> >> >Department: Support IDV
> >> >Priority: Normal
> >> >Status: Open
> >> >
> >> >
> >> >
> >> >
> >>
> >>
> >>
> >>
> >>
> >>
> >
> >
> >Ticket Details
> >===================
> >Ticket ID: COT-972342
> >Department: Support IDV
> >Priority: Normal
> >Status: Open
> >
> >
> >
> >
> 
> 
> 
> 
> 
> 


Ticket Details
===================
Ticket ID: COT-972342
Department: Support IDV
Priority: Normal
Status: Open