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DCL:GRPH1:STPACK: Transformation Functions:Explanation of Subroutines: Coordinate Transformation (Subroutines)

6.4.1 STFTRN/STITRN/STSTRN

1.

Function

Performs a normalization transformation (transformation of UC and VC) or map projection (transformation of TC and VC).

2.

Call

CALL STFTRN(UX,UY,VX,VY)
CALL STITRN(VX,VY,UX,UY)
CALL STSTRN(ITR,CXA,CYA,VX0,VY0)

3.

Explanation of Arguments

UX,UY	(R)	The coordinates of UC/TC
VX,VY	(R)	The coordinates of VC.
ITR	(I)	Transformation function number
CXA,CYA	(R)	Factor to multiply coordinate value by
VX0,VY0	(R)	The position of the origin in VC

4.

Notes

(a)

In a map projection, if transformation is impossible due to factors such as singular points, the value of the internal variable RUNDEF managed by GLpGET/GLpSET is returned. (The initial value is -999.0.)

(b)

This function performs the following operations.

• Performs a basic transformation on (UX,UY)  to (XX,YY) according to the transformation function number
• Furthermore, it expands or shifts by 

  VX = CXA*XX + VX0
  VY = CYA*XX + VY0
  .