;
; compute how the errors change as you move the center
; start with xyz
; pass in delta radius
; we will change radius and the z offset of the center to compensate
;  
; xyz[3,n] : measurements in meters
; dr       : change in radius to use (meters)
;
; keywords: 
; cendef[3]: double .. if not supplied use the 3param fit center 
; raddef   : double .. default radius . def 265.176m
;
; compute the errors using the measured xyz points.
; and
;  (radDef + dr )  so +dr will make radius longer
;   when computing this, move the zcen in the dr direction
;                                
function cmperrradius,xyz,radToUse, cendef=cendef,radDef=radDef
;
;
	if (n_elements(cendef) ne 3) then cendef=[.0213d,.0202d,264.4778d]
	if (n_elements(radDef) eq 0) then radDef=265.176d
;
	dr=radToUse - radDef
	centToUse=cenDef
	centToUse[2]+=dr  ;  since changing radius will change the zoffset of the center.
	rtp=blmxyztosph(xyz,cent=centToUse,/deg)
;   compute the std error
;
	return,(reform(rtp[0,*]) - radToUse)*100.
end