;
; plot errors as we change the location of the center
;
; 3 param fit:   radius : 265.176
; 4 param fit:   radius : 265.1001
; zcenter moved by just about the change in radius
;
; plot what the radial errors would be if we used a 265.176 radius
;  on a dish that had a true radius of 265.1000 meters
;                0 
radius3=265.176d
radius4=265.1001d
xcen4=0.
zcen4=radius4
xcen3=0.
zcen3=radius3
elMax=34.
thMax= elMax - 90.
thMin= thMax - 2*elMax
arc=[thmin,thmax]
;
if hard then pscol,'errVsCenter.ps',/full
!p.multi=[0,1,2]
hor, -140,140
ver,-1,42
xtit='x distance [meters]'
ytit='z distance [meters]'
cs=1.4
font=1
tit='xz slice of sphere'
drawcircle,xcen4,zcen4,radius4,npnts=npnts,arc=arc,$
		chars=cs,font=font,$
		xret=xret4,yret=zret4,$
		xtit=xtit,ytit=ytit,$
		tit=tit
drawcircle,xcen3,zcen3,radius3,npnts=npnts,arc=arc,/over,col=2,$
		xret=xret3,yret=zret3
csn=1.5
ln=2
xp=.2
scl=.7
note,ln      ,"radius = 265.100 meters",chars=csn,font=font,xp=xp,col=colph[1]
note,ln+1*scl,"radius = 265.176 meters",chars=csn,font=font,xp=xp,col=colph[2]
;
; compute  the radial error by moving center to ycen3 and then compute errors you'd get
; from radius3
;
	rNew= sqrt( xret4^2 + (zret4-zcen3)^2)
	rerr= rnew -radius3
	tit='radial error using 265.176[m] radius for 265.1[m] curvature'
	ver,-1.2,.1
	ytit='Radial error [cm]'
	plot,xret4,rerr*100.,$
		chars=cs,font=font,$
		xtit=xtit,ytit=ytit,$
		tit=tit
ln=17
xp=.04
note,ln,"<0 --> radius too short",chars=csn,font=font,xp=xp
;
; look at error my shifting x by 2 cm.
;
	ver,-1.2,1.2
	dxShift=.02d
	rNew= sqrt( (xret4 - dxShift)^2 + (zret4-zcen4)^2)
	rerr=rnew  - radius4
	ytit='Radial error [cm]'
	tit='Radial error cause by shifting xCenter by 2 cm in the +x direction'
	plot,xret4,rerr*100. ,$
		chars=cs,font=font,$
		xtit=xtit,ytit=ytit,$
		tit=tit
;
;   look at the 3 and 4 parameter fits.
; - generate a sphere using the 4 parameter fit
; - and then try a 3 paramer fit to it.. see what it does tothe center and radius
;
	nodata=-999.
	eps=.01
	zaDmax=35.
	radius=rad4
	npnts=100l
	ngood=xyzgridsph(zadmax,radius,npnts,xyzgrid)
	ii=where(abs(xyzgrid[0,*,*] - nodata) lt eps,cnt1)
;
; 	add some noise to the z position
;
	xyzgrid[2,*,*]+=randomN(0,100,100)*.03
;
;	now fit to the sphere
;
	x0=0.
	y0=0.
	z0=0.
	eps=.1
	r=rad4 + eps
	fitA=[1.,1.,1.,1.] ; fit all 4 params
	initCoef=[x0,y0,z0,r]
	ntot=npnts*npnts
	istat=blmfitsphere(reform(xyzgrid,3,ntot),fitA=fitA,fitICf,initCoef=initCoef,fitRadDif=fitraddif)
	print,fiticf.fitcoef
	print,fiticf.sigmas


;

;   and try fitting for the 
	if hard then hardcopy
	x
	ldcolph
end