NASA Ocean Color

ocssw V2022
 **                                                                              
 ** INVOCATION NAME:  DANGLE                                                     
 **                                                                              
 ** PURPOSE:  FUNCTION TO COMPUTE THE ANGLE BETWEEN TWO UNIT VECTORS             
 **                                                                              
 ** INVOCATION METHOD:  X = DANGLE(A, B, TOLER, ANG)                             
 **                                                                              
 ** ARGUMENT LIST:                                                               
 ** NAME    TYPE  USE PURPOSE                                                    
 ** A(3)    R*8    I  FIRST UNIT VECTOR                                          
 ** B(3)    R*8    I  SECOND UNIT VECTOR                                         
 ** TOLER   R*8    I  MAXIMUM MAGNITUDE OF DOT-PRODUCT BEFORE CROSS-             
 **                   PRODUCT IS USED TO COMPUTE ANGLE.  IF DOT-PRODUCT          
 **                   IS GREATER THAN TOLER, THEN THE ANGLE IS ARCSIN            
 **                   OF THE MAGNITUDE OF THE CROSS-PRODUCT, OTHERWISE,          
 **                   THE ARCCOS OF THE DOT-PRODUCT IS USED.                     
 **                   (RECOMMENDED VALUE IS 0.99D0)                              
 ** ANG     R*8    O  ANGLE BETWEEN UNIT VECTORS A AND B IN RADIANS              
 ** DANGLE  R*8    O  ANGLE BETWEEN UNIT VECTORS A AND B IN RADIANS              
 **                                                                              
 ** FILE/RECORD REFERENCES: NONE                                                 
 **                                                                              
 ** GLOBAL REFERENCES: NONE                                                      
 **                                                                              
 ** EXTERNAL REFERENCES: NONE                                                    
 **                                                                              
 ** INTERNAL VARIABLES:                                                          
 ** VAR       TYPE  PURPOSE                                                      
 ** ACROSB(3) R*8   CROSS-PRODUCT OF A AND B                                     
 ** ADOTB     R*8   DOT-PRODUCT OF A AND B                                       
 ** CROSMG    R*8   MAGNITUDE OF CROSS-PRODUCT                                   
 **                                                                              
 ** NOTES:                                                                       
 **                                                                              
 ** CHANGE HISTORY:                                                              
 ** AUTHOR             CHG-ID   MMM.YY    CHG-SUMMARY                            
 ** B.GROVEMAN                  JUL.88    PDL                                    
 ** M.WOOLSEY                   AUG.88    CERTIFIED PDL                          
 ** R.COON                      NOV.88    ORIGINAL CODE                          
 ** B.GROVEMAN                  NOV.88    CERTIFIED CODE                         
 ** M. WOOLSEY                  AUG.89    CORRECTED ARCSIN METHOD                
 **                                        RETURNING ANSWERS > PI / 2            
 **                                                                              
 ** BEGIN PDL                                                                    
 **      COMPUTE DOT-PRODUCT OF A AND B                                          
 **      IF (DOT-PRODUCT LESS THAN TOLER) THEN                                   
 **         ANGLE = ARCCOS(DOT-PRODUCT)                                          
 **      ELSE                                                                    
 **         COMPUTE CROSS-PRODUCT OF A AND B                                     
 **         COMPUTE THE MAGNITUDE OF THE CROSS-PRODUCT                           
 **         ANGLE = ARCSIN(MAGNITUDE OF CROSS-PRODUCT)                           
 **         IF (DOT-PRODUCT IS LESS THAN ZERO) ANGLE = PI - ANGLE                
 **      END IF                                                                  
 **                                                                              
 **      RETURN                                                                  
 ** END PDL                                                                      
 **                                                                              
 ** MAIN ENTRY POINT TO DANGLE                                                   
 ************************************************************************        
 C                                                                               
       FUNCTION dangle (A, B, TOLER, ANG)                                        
 C                                                                               
 C-----DECLARE ARGUMENTS                                                         
       real*8 a(3), b(3), toler, ang, dangle                                     
 C                                                                               
 C-----DECLARE LOCAL VARIABLES                                                   
       real*8 acrosb(3), adotb, crosmg                                           
       real*8 pi /3.141592653589793d+00/                                         
 C                                                                               
       adotb = a(1)*b(1) + a(2)*b(2) + a(3)*b(3)                                 
       IF (abs(adotb) .LE. abs(toler)) THEN                                      
 C                          USE DOT-PRODUCT                                      
         ang = acos(adotb)                                                       
         dangle = ang                                                            
       ELSE                                                                      
 C                          USE CROSS PRODUCT FOR GREATER ACCURACY               
         acrosb(1) = a(2)*b(3) - a(3)*b(2)                                       
         acrosb(2) = a(3)*b(1) - a(1)*b(3)                                       
         acrosb(3) = a(1)*b(2) - a(2)*b(1)                                       
         crosmg = sqrt(acrosb(1)**2 + acrosb(2)**2 + acrosb(3)**2)               
         ang = asin(crosmg)                                                      
         IF (adotb .LT. 0.0d0)  ang = pi - ang                                   
         dangle = ang                                                            
       END IF                                                                    
 C                                                                               
       RETURN                                                                    
       END
real
#define real
Definition: DbAlgOcean.cpp:26
#define pi
Definition: vincenty.c:23
abs
#define abs(a)
Definition: misc.h:90
dangle
real *8 function dangle(A, B, TOLER, ANG)
Definition: dangle.f:62