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[IDV #EWA-848337]: Method to convert Pressure field to Height Field

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  • Subject: [IDV #EWA-848337]: Method to convert Pressure field to Height Field
  • Date: Sat, 24 Dec 2011 09:29:09 -0700
 
> >
> R/Sir
> 
> Thanks a lot again.
> I am afraid, new Unit() may not be applicable for converting pressure to
> altitude. I think we need to go through some coordinate system conversion.
> The one I chose was Standard Atmospheric Coordinate System.
> Well frankly speaking, this is not my original idea. I was just going
> through getInitialSpatialDomain(GeoGrid geogrid) method in
> ucar.unidata.data.grid.GeoGridAdapter class. And I found that this is
> one way to convert pressure to altitude. Am I going wrong somewhere?
> Is this not the right way to convert Pa/hPa or millibar to meters. I
> know little about science. Please correct me if I am wrong. Actually I
> was just thinking that if you had such similar stuff in derived.xml,
> that could be utilized for converting pressure to height.
> 

Ghansham,
      I am still not quite sure if going through the coordinate conversion is 
the smart way to do it. There is a formula can be used to define the relation 
between pressure and altitude in the following URL:

https://www.brisbanehotairballooning.com.au/faqs/education/113-pressure-altitude-conversion.html

This maybe better.

> I will describe you in detail why I need all this stuff. Actually we
> have our wind vector data product in HDF5 as Point Data (Compound Datasets).
> I mean
> Lat/Lon/UComp/VComp/WindSpeed/WindDirection/Pressure
> 
> I created a datasource class that extends PointDataSource and does
> barnes analysis. And generates almost everything as expected.
> 
> In between one query related to this, I was just going through
> ucar.unidata.data.point.PointDataSource class. Why the
> makeDerivedDataChoices method has been over-ridden like this:
> 
> protected void makeDerivedDataChoices(List dataChoices) {}
> 
> Any special reason?

I don't know, I need to check the source code when I back to office after new 
year.
> 
> I just over-ridded this method to generate Wind Vectors (using UComp and
> VComp) by using derived.xml. And I came to know about a few more
> meteorology specific stuff: vorticity, advection, etc.
> Now I was just trying to do some thing like Wind Vectors draped over
> topography. The topography I was trying to generate was by using
> pressure values. That is why I had to write the createHeightField()
> method taking pressure field as input.
> 

> And one more display control, I am planning to build up is 'Wind Vector
> shaded by another parameter'. This another parameter I am planning to
> use is Pressure. The reason is the  scientists dealing with winds here
> use such displays for their analysis.


You can use the formula "Formula > Grids > One value colored by another" to do 
this.

Yuan
> 
> I am cc'ing this mail to Don Sir too in case he has something to say.
> 
> I am bad in communicating at times. Please do revert back if I am
> ambiguous somewhere.
> 
> regards
> Ghansham
> 
> 


Ticket Details
===================
Ticket ID: EWA-848337
Department: Support IDV
Priority: Normal
Status: Open