[ncl-talk] mean value of all displayed grid points / pixel in a map

Kreienkamp Frank Frank.Kreienkamp at dwd.de
Thu Sep 4 04:25:18 MDT 2014 

Yes the idea of removing all grid points that are not displayed might be an solution.

But from my current view I have several problems. The two central are:

a)      I define the plot parameter using:

   res at mpProjection                  = "Stereographic"

   res at mpCenterLatF                  = 50                 ; Centered over Germany

   res at mpCenterLonF                  = 10                 ; Centered over Germany

   res at mpLimitMode                   = "Corners"          ; choose range of map

   res at mpLeftCornerLatF              =  55.8

   res at mpLeftCornerLonF              =   2.6

   res at mpRightCornerLatF             =  45.1

   res at mpRightCornerLonF             =  19.5

So two points of the rectangle are missing. If the res at mpCenterLonF is not central, calculating the two needed points is not easy.

b)      What to do with points which are only partly drawn. I would like to have this part inside the average value. For fine grids with many points, missing few might not be an issue. With coarse grids this might produce a problem.

My hope was, that there is point when I can catch a ‘transfer array’ in the moment when the grid is transferred to the (png-) workstation, after all the projection part is done. Like there would be an matrix of points(pixel) which are displayed.

Thank for your help
Frank

Von: ncl-talk-bounces at ucar.edu [mailto:ncl-talk-bounces at ucar.edu] Im Auftrag von Maria Gehne - NOAA Affiliate
Gesendet: Mittwoch, 3. September 2014 17:31
An: Kreienkamp Frank
Cc: ncl-talk
Betreff: Re: [ncl-talk] mean value of all displayed grid points / pixel in a map

Hi Frank,

how are you deciding which area to plot? You must have something in your code that limits the area shown in the figure. Why don't you just use coordinate indexing to extract the region of interest from your data and set everything else to _FillValue. That way you can compute the area average and only the points that are not missing will be used for the average. Is that what you were looking for?

Maria

On Wed, Sep 3, 2014 at 12:07 AM, Kreienkamp Frank <Frank.Kreienkamp at dwd.de<mailto:Frank.Kreienkamp at dwd.de>> wrote:
Hello Dennis,

if i read the webpage correctly the suggested functions are not what i am looking for.

Yes, I am looking for an areal average.

No, it is not for an rectangular grid.

I have an rectangular grid as the ‘base’. Using this grid and a polar stereographic projection I am drawing a map. This map is showing  only a part of the hole ‘base’ grid. I am looking for an average of this shown/drawn part.

Writing the same from a different view. I am looking for a function what calculates the average values of the presented map. See the example in my previous e-mail.

As far a I understand the description correctly this in not what the function wgt_areaave_wrap provides.

Thanks in advance
Frank

Von: Dennis Shea [mailto:shea at ucar.edu<mailto:shea at ucar.edu>]
Gesendet: Montag, 1. September 2014 16:13

An: Kreienkamp Frank
Cc: ncl-talk
Betreff: Re: [ncl-talk] mean value of all displayed grid points / pixel in a map

As previously noted:

For a rectilinear grid: wgt_areaave_Wrap calculates an area average
https://www.ncl.ucar.edu/Document/Functions/Contributed/wgt_areaave_Wrap.shtml
For a curvilinear grid: http://www.ncl.ucar.edu/Document/Functions/Built-in/wgt_areaave2.shtml
or a simple arithmetic average: avg

http://www.ncl.ucar.edu/Document/Functions/Built-in/avg.shtml



On Mon, Sep 1, 2014 at 7:57 AM, Kreienkamp Frank <Frank.Kreienkamp at dwd.de<mailto:Frank.Kreienkamp at dwd.de>> wrote:
Hello Dennis,

sorry that my question wasn’t clear enough.

Let my try again.
The attached map is a displayed result of RCM-dataset. The original grid covers Europe. The displayed area covers Germany and a bit more.

What I am looking for is a routine that calculates the mean value of the displayed area.

Thanks in advance
Frank

Von: ncl-talk-bounces at ucar.edu<mailto:ncl-talk-bounces at ucar.edu> [mailto:ncl-talk-bounces at ucar.edu<mailto:ncl-talk-bounces at ucar.edu>] Im Auftrag von Dennis Shea
Gesendet: Montag, 1. September 2014 15:11
An: Kreienkamp Frank
Cc: ncl-talk
Betreff: Re: [ncl-talk] mean value of all displayed grid points / pixel in a map

The question is vague

"I want to calculate the mean value of all displayed grid points in a map.

This means:
- i have gridded data for the entire world (gcm-results)
- i plot a map (stereographic projection) for Europe

NCL draws a rectangle map based on the given resource parameters. I am
looking for a function which counts all displayed values (pixel?) and
calculates an average value."
NCL handles "gridded data for the entire world (gcm-results)" all the time.

[1]  dim_avg_n_Wrap will calculate the means at each grid point over all times.
[2] wgt_areaave_Wrap calculates an area average
[3] NCL can display much more than a "rectangular map"
[4] wks = gsn_open_wks("png" ,"frank")
     will send graphics to a png file
What do you mean by:

"Is there a chance that i can get the matrix-values which are send to the (png-)workstation?"

=======
https://www.ncl.ucar.edu/Document/Functions/Contributed/dim_avg_n_Wrap.shtml
https://www.ncl.ucar.edu/Applications/climo.shtml
https://www.ncl.ucar.edu/Document/Functions/Contributed/wgt_areaave_Wrap.shtml
https://www.ncl.ucar.edu/Applications/maponly.shtml
 https://www.ncl.ucar.edu/Document/Graphics/Interfaces/gsn_csm_contour_map.shtml
Good luck

On Mon, Sep 1, 2014 at 2:31 AM, Kreienkamp Frank <Frank.Kreienkamp at dwd.de<mailto:Frank.Kreienkamp at dwd.de>> wrote:
Hello ,

since having no one answering the original question.

Is there a chance that i can get the matrix-values which are send to the (png-)workstation?

Thanks in advance
Frank Kreienkamp

-----Ursprüngliche Nachricht-----
Von: ncl-talk-bounces at ucar.edu<mailto:ncl-talk-bounces at ucar.edu> [mailto:ncl-talk-bounces at ucar.edu<mailto:ncl-talk-bounces at ucar.edu>] Im Auftrag von Frank Kreienkamp
Gesendet: Mittwoch, 27. August 2014 06:37
An: ncl-talk
Betreff: [ncl-talk] mean value of all displayed grid points / pixel in a map

Hello,

i have searched the function list but i have not found a solution for the following problem.

I want to calculate the mean value of all displayed grid points in a map.

This means:
- i have gridded data for the entire world (gcm-results)
- i plot a map (stereographic projection) for Europe

NCL draws a rectangle map based on the given resource parameters. I am looking for a function which counts all displayed values (pixel?) and calculates an average value.

Thanks in advance
Frank
_______________________________________________
ncl-talk mailing list
List instructions, subscriber options, unsubscribe:
http://mailman.ucar.edu/mailman/listinfo/ncl-talk
_______________________________________________
ncl-talk mailing list
List instructions, subscriber options, unsubscribe:
http://mailman.ucar.edu/mailman/listinfo/ncl-talk


_______________________________________________
ncl-talk mailing list
List instructions, subscriber options, unsubscribe:
http://mailman.ucar.edu/mailman/listinfo/ncl-talk


_______________________________________________
ncl-talk mailing list
List instructions, subscriber options, unsubscribe:
http://mailman.ucar.edu/mailman/listinfo/ncl-talk

-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://mailman.ucar.edu/pipermail/ncl-talk/attachments/20140904/c85d6cec/attachment.html

More information about the ncl-talk mailing list