Vector Angles

From: Kevin Rosser (kevin_rosser@XXXXXX)
Date: Thu Dec 12 2002 - 11:51:18 MST


I have been using the vvinit/vvectr combo to produce vector maps of NOAA
   wind data sets. The data set has vector speed (m/s) and angles
(degrees). I made a dummy data set that provided vectors in a constant
change of direction from 000-360 and the results are not 000-360. For
instance the portion from 000-035 looks more like 000-090 degrees. A 5
degree change looks like 30 degrees in change on the plot.

Odd thing about it the 0-90-180-270 arrows are in the right directions
but the amounts in-between are greatly exaggerated.

I have set PLR to 1 prior to making the vvinit call. In all other
aspects the plot looks correct.

Below is an excerpt of my call to vector plot.

c********Set up vectors
c CALL VVRSET
       CALL SET (.1,.95,.20,.90,00.,25.,0.0,wtop,1)
       CALL VVSETI ('SET - DO-SET-CALL-FLAG',0)
       CALL VVSETR ('XC1 - X COORDINATE AT INDEX 1',1.)
       CALL VVSETR ('XCM - X COORDINATE AT INDEX M',24.)
       CALL VVSETR ('YC1 - Y COORDINATE AT INDEX 1',wbot)
       CALL VVSETR ('YCN - Y COORDINATE AT INDEX N',wtop)
c********PLR 1= U ARRAY IN VECTOR MAG, V ARRAY IN < DEGREES
       CALL VVSETI ('PLR - POLAR INPUT MODE',1)
         CALL VVSETI ('AST - ARROW STYLE',1)
         CALL VVSETI ('SVF - SPECIAL VALUE FLAG',3)
         CALL VVSETR ('USV - SPECIAL VALUE',999.9)
         CALL VVSETR ('VSV - SPECIAL VALUE',999.)
       CALL VVINIT (ms,LX,angle,LX,ZDAT,LX,LX,23,WRK,0)
         CALL VVSETR ('VRM - VECT REF MAG',20.)
         CALL VVSETC ('MNT - MIN VECT REF','Reference Low Vector')
         CALL VVSETC ('MXT - MAX VECT REF','Reference High Vector')
c********call to move the min-max text for wind barbs
        CAll VVSETR ('MNX - MIN VECTOR TEXT BLOCK X CORD',.4)
       CALL VVSETR ('MNY - MIN VECTOR TEXT BLOCK Y CORD',-.06)
       CALL VVSETR ('MXX - MAX VECTOR TEXT BLOCK X CORD',.5)
       CALL VVSETR ('MXY - MAX VECTOR TEXT BLOCK Y CORD',-.06)
       CALL VVECTR (ms,angle,IDM,IDM,IDM,IDM)
       CALL LABMOD ('(F5.0)','(F5.3)',0,0,0,0,0,0,0)
       CALL GRIDAL (5,0,37,0,1,1,5,10.,0.)
       CALL SET (0.,1.,0.,1.,0.,1.,0.,1.,1)
       CALL WTSTR (.4,.95,station,2,0.,0.)
       CALL WTSTR (.5,.95,date(I,J-2),2,0.,0.)
       CALL PLCHHQ (.03,.6,'HEIGHT IN KILOMETERS',.012,90.,0.)
       CALL PLCHHQ (.5,.1,'TIME OF DAY (PST) HOUR 1-24',.012,0.,0.)

         CALL FRAME

-- 
Kevin Rosser
Environmental Planner
Tehama County, CA

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