SUBROUTINE W3FT02 (RAIN, IMAX, JMAX, PI, PJ, AMOUNT)
C$$$ SUBPROGRAM DOCUMENTATION BLOCK
C
C SUBPROGRAM: W3FT02 INTERPOLATE PRECIPITATION TO SPECIFIC POINT
C PRGMMR: HIRANO ORG: NMC24 DATE:96-06-23
C
C ABSTRACT: INTERPOLATE, USING A FANCY NON-LINEAR METHOD,
C GRIDDED QUANTITATIVE PRECIPITATION FORECASTS TO A SPECIFIC
C INTERIOR POINT. ONE POINT (E.G. AN OBSERVATION STATION)
C PER CALL TO W3FT02.
C
C PROGRAM HISTORY LOG:
C 79-08-05 R.HIRANO
C 96-06-23 farley converted to cray fortran 77
C
C USAGE: CALL W3FT02(RAIN, IMAX, JMAX, PI, PJ, AMOUNT)
C
C INPUT VARIABLES:
C NAMES INTERFACE DESCRIPTION OF VARIABLES AND TYPES
C ------ --------- -----------------------------------------------
C RAIN ARG LIST REAL*4 GRID FIELD OF (FORECAST) PRECIPITATION
C IMAX ARG LIST INTEGER*4 I-DIMENSION OF RAIN FIELD
C JMAX ARG LIST INTEGER *4 J-DIMENSION OF RAIN FIELD
C PI ARG LIST REAL*4 I-COORDINATE OF INTERPOLATION POINT
C PJ ARG LIST REAL*4 J-COORDINATE OF INTERPOLATION POINT
C
C OUTPUT VARIABLES:
C NAMES INTERFACE DESCRIPTION OF VARIABLES AND TYPES
C ------ --------- -----------------------------------------------
C AMOUNT ARG LIST REAL*4 AMOUNT OF PRECIP INTERPOLATED TO PI,PJ
C
C SUBPROGRAMS CALLED:
C NAMES LIBRARY
C ------------------------------------------------------- --------
C AMAX1 SYSTEM
C
C ATTRIBUTES:
C LANGUAGE: IBM VS FORTRAN
C MACHINE: NAS-9050, 9070
C
C NO WRITEUP AVAILABLE. SEE PROGRAMMER FOR ADDITIONAL INFORMATION.
C
C$$$
C
C INTERPOLATE PRECIPITATION FROM RAIN FIELD
C TO INTERNAL POINT (PI,PJ). RESULT IN AMOUNT
C
real RAIN(IMAX,JMAX)
C
C CHECK FOR INTERPOLATION POINT OUTSIDE GRID
C
AMOUNT = 0.
IF(PI.LE.1.OR.PI.GE.IMAX) GO TO 150
IF(PJ.LE.1.OR.PJ.GE.JMAX) GO TO 150
C
C SET UP RAIN AMMOUNTS AT CORNERS OF BOX SURROUNDING POINT (PI,PJ
C
C R2 R4
C
C (PI,PJ)
C
C R1 R3
C
I=PI
J=PJ
R1=RAIN(I ,J )
R2=RAIN(I ,J+1)
R3=RAIN(I+1,J )
R4=RAIN(I+1,J+1)
C
C CHECK FOR NO RAIN AT ALL
C
IF(AMAX1(R1,R2,R3,R4).LE.0.) GO TO 150
C
C GOT SOME -- FIND APPROPRIATE SECTOR AND SECTION
C OF THE GRID BOX IN WHICH THE STATION IS LOCATED
C
AI = PI-I
AJ=PJ-J
X = 0.5
C
C MEANINOF IC FOR SECTORS (K=1) OR SECTIONS (K=2)
C
C 2 4
C
C 1 3
C
C ALSO REFERENCED AS
C
C TOP DIAGONAL / T D
C /
C NEAR RIGHT / N R
C
DO 1 K=1,2
IF(AI.GT.X) GO TO 2
IF(AJ.GT.X) GO TO 4
IC = 1
GO TO 10
4 CONTINUE
IC = 2
GO TO 10
2 CONTINUE
IF(AJ.GT.X) GO TO 6
IC = 3
GO TO 10
6 CONTINUE
IC = 4
10 CONTINUE
IF(K.NE.1) GO TO 16
C
C SET UP SECTORS THIS BUSINESS IN EFFECT ROTATES THE SECTORS
C FOR CONVENIENCE IN LATER INTERPOLATIONS
C
GO TO (11, 12, 13, 14), IC
11 CONTINUE
R = R1
RT = R2
RR = R3
RD = R4
GO TO 15
12 CONTINUE
R = R2
RT = R1
RR = R4
RD = R3
AJ = 1. - AJ
GO TO 15
13 CONTINUE
R = R3
RT = R4
RR = R1
RD = R2
AI = 1. - AI
GO TO 15
14 CONTINUE
R = R4
RT = R3
RR = R2
RD = R1
AI = 1. - AI
AJ = 1. - AJ
15 CONTINUE
C
C IF NO RAIN IN CORNER SECTTOR WHERE STATION IS - QUIT
C
IF(R.LE.0.) GO TO 150
X = 0.5 * X
16 CONTINUE
1 CONTINUE
C
C INTERPOLATE TO STATION IN EASY (NON-CORNER) SECTIONS
C
GO TO (21, 22, 23, 24), IC
21 CONTINUE
AMOUNT = R
GO TO 150
22 CONTINUE
RC = RT
RX = AJ
GO TO 120
23 CONTINUE
RC = RR
RX = AI
120 CONTINUE
IF(RC.GT. 0.) GO TO 130
AMOUNT = R - R*(RX-X)/X
GO TO 150
130 CONTINUE
AMOUNT = R + (0.5*(R+RC)-R)*(RX-X)/X
GO TO 150
24 CONTINUE
C
C CORNER (CENTER OF BOX) SECTION
C
AA = AMAX1(RR, RT, RD)
IF(AA.GT.0.) GO TO 30
RS = 0.
RU = 0.
RD = 0.
GO TO 37
30 CONTINUE
IF(RR.GT.0.) GO TO 32
RS = 0.
RRD = 0.
33 CONTINUE
IF(RT.GT.0.) GO TO 34
RU = 0.
RTD = 0.
GO TO 35
34 CONTINUE
RU = 0.5 * (R+RT)
IF(RD.GT.0.) GO TO 36
RTD = 0.
GO TO 35
36 CONTINUE
RTD = 0.5 * (RT + RD)
GO TO 35
32 CONTINUE
RS = 0.5 * (R+RR)
IF(RD.GT.0.) GO TO 38
RRD = 0.
GO TO 33
38 CONTINUE
RRD = 0.5 * (RD + RR)
GO TO 33
35 CONTINUE
RD = 0.25 * (RS + RU + RTD + RRD)
IF(RS.LE.0. .AND. RTD.LE.0.) RD = 0.
IF(RU.LE.0..AND.RRD.LE.0.) RD=0.
RU = RU + (RD-RU) * (AI-X)/X
37 CONTINUE
R = R + (RS-R) * (AI-X)/X
AMOUNT = R + (RU-R) * (AJ-X)/X
150 CONTINUE
RETURN
C
END