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Re: Composite image based on irregular months



Hi Yun,
This is something that's not straitforward to do in Ferret; I got
some ideas by looking up the word "recusive" in the mail list
archives; as you probably found, using a loop  you cannot just
do a simple sum in the form  "let sum = sum + slp[l=409]".
This is a recursive definition that cannot be used.  Instead we will
define a new variable at each step in making the sum, and add the
previous sum to our new variable.  Here is an example with one
of the data sets included with Ferret:

! Open the data set.  Make a list of time steps to choose for the sum.
! This can also be a list along another axis, i.e. ZSEQUENCE, and
! then the loop below would be a REPEAT/K=

  yes? USE coads_climatology
  yes? LET choose = TSEQUENCE({2,3,6,8,9,12})
  yes? LET npts = `choose,RETURN=LSIZE`

! Initialize the sum.  You might want to use a different initialization to
! assign missing values to locations where there is never any data.
! On each repeat, make a new variable with the current sum.

  yes? LET sum0 = 0*x[GX=sst] + 0*y[GY=sst]

  yes? REPEAT/L=1:`npts` (LET ttime = choose[L=`L`]; \
       LET sum`L` = sum`L-1` + sst[L=`L`]; \
       SHADE sum`l`; PAUSE)

Ansley
 

Yun.Li@csiro.au wrote:

 

Dear Ferret users,

I am trying to make a composite image based on some irregular months of an index. For example, I want a composite image of sea level pressure (SLP) based on irregular months such as L=409, 505, 576 and 625 from the following data in ferret.

2> /data/necp/slp_mon_1948_2002
name     title       I         J         K         L
 SLP      slp        1:144     1:73      1:1       1:660

So far, I can only use the following awkward way to make it, that is,

Let P=(slp[d=2, L=409] + slp[d=2, L=505] + slp[d=2, L=576] + slp[d=2, L=625])/4
Fill P

I would appreciate your help on creating the composite image in another simple way based on irregular months, in particular, when the number of irregular months is big.
 

Best wishes,

Yun
 

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Dr. Yun Li
Environmetrics (www.cmis.csiro.au/envir)
CSIRO Mathematical and Information Sciences
Private Bag 5, Wembley, WA 6913, Australia
Phone: +61 8 9333 6388  Fax: +61 9333 6121
URL: http://www.cmis.csiro.au/Yun.Li/
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

--
Ansley Manke  Pacific Marine Environmental Laboratory  Seattle WA
 


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