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OPTIONS(/e);
EXTERNAL CLASS figure;

COMMENT: This procedure will construct a coordinate system
suitable for a figure within the limits xmin,xmax
and ymin,ymax along x- and y-axis respectively.

Version 2, march 1975
Author: Ake Blomberg, FOA, Sweden.                ;

REF(figure) PROCEDURE cosysfor(xmin,xmax,ymin,ymax);
REAL xmin,xmax,ymin,ymax;
BEGIN

    REAL xleft,yleft,xlift,yshift,sx,sy,xstep,ystep,ox,oy,temp;
    INTEGER i,zerox,zeroy,xtics,ytics;
    TEXT labe;
    REF(figure) c;

    PROCEDURE axis (min,max,metric,left,tics,scale,ztep,zeropos);
    NAME left,tics,scale,ztep,zeropos;
    REAL min,max,metric,left,scale,ztep;
    INTEGER tics,zeropos;

    BEGIN
	REAL width,right,bigleft,bigright,bigztep,p10,b10,a;
	INTEGER nleft,nright,nbig,i,p;
	width:=max-min;
	p:=Entier(Ln(width)/Ln(10));
	p10:=10**p; a:=width/p10; b10:=10*p10;
	ztep:= IF a<=2 THEN 0.2*p10 ELSE IF a<=6 THEN 0.5*p10 ELSE p10;
	nleft:=Entier(min/ztep); nright:=Entier(max/ztep)+1;
	IF Abs(nleft-nright) >= 4 THEN
	BEGIN
	    IF a>2 AND a<=6 AND Mod(nleft,2) NE 0 THEN nleft:=nleft-1;
	    IF a>2 AND a<=6 AND Mod(nright,2) NE 0 THEN nright:=nright+1;
	END;
	left:=nleft*ztep; right:=nright*ztep;
	bigztep:=IF a<=5 THEN p10 ELSE b10; nbig:=Entier(left/bigztep);
	bigleft:=nbig*bigztep;
	IF left-bigleft <= ztep THEN left:=bigleft;
	bigright:=bigleft+bigztep;
	IF bigright>right AND bigright<=right+ztep THEN
	right:=bigright;
	width:=right-left;
	nleft:=Entier(left/ztep); nright:=Entier(right/ztep);
	scale:=metric/width; ztep:=scale*ztep;
	zeropos:=IF min*max > 0 THEN -1  ELSE -nleft;
	tics:=Abs(nleft-nright)+1;
    END***axis***;
    labe:-Blanks(10);

    axis(xmin,xmax,750,xleft,xtics,sx,xstep,zerox);
    axis(ymin,ymax,500,yleft,ytics,sy,ystep,zeroy);

    xlift:=IF zeroy>=0 THEN 200+zeroy*ystep  ELSE 200;
    yshift:=IF zerox>=0 THEN 150+zerox*xstep  ELSE 150;
    ox:=150-sx*xleft; oy:=200-sy*yleft;

    c:-NEW figure;
    c.moveto(yshift,700); c.drawto(yshift,200);
    c.moveto(150,xlift); c.drawto(900,xlift);

    temp:=200-ystep;
    FOR i:=1 STEP 1 UNTIL ytics DO
    BEGIN temp:=temp+ystep;
	c.moveto(yshift+4,temp); c.drawto(yshift-4,temp);
    END;

    temp:=150-xstep;
    FOR i:=1 STEP 1 UNTIL xtics DO
    BEGIN temp:=temp+xstep;
	c.moveto(temp,xlift+4); c.drawto(temp,xlift-4);
    END;
    c.moveto(180,110);
    c.write("x-axis:  y=");  labe.Setpos(1);
    IF zeroy >=0 THEN labe.Putchar('0') ELSE labe.Putreal(yleft,4);
    c.write(labe);
    c.moveto(500,110);
    labe.Setpos(1); labe.Putreal(xstep/sx,4);
    c.write("x-step ="); c.write(labe);

    c.moveto(180,150);  labe:="          ";
    c.write("y-axis:  x=");  labe.Setpos(1);
    IF zerox >=0 THEN labe.Putchar('0') ELSE labe.Putreal(xleft,4);
    c.write(labe);
    c.moveto(500,150);
    labe.Setpos(1); labe.Putreal(ystep/sy,4);
    c.write("y-step ="); c.write(labe);

    c.scale_y:=sy; c.origin_y:=oy;
    c.scale_x:=sx; c.origin_x:=ox;

    cosysfor:-c;


END********************************************************