function WDETREND, sig, TT
;+
;NAME:
;	WDETREND
;
;PURPOSE:
;	To remove a linear bias from the "sig" data array.
;
;CATEGORY:
;	Wavelets
;
;CALLING SEQUENCE:
;	out = WDETREND(sig)
;
;INPUTS:
;	sig	= current data array/signal
;
;OUTPUTS:
;	out = now detrended data array/signal
;	TT = 'I' if image and 'S' if signal
;
;EXAMPLE
;		IDL> ;Truncate sig array appropriately and get QMF
;		IDL> WINTWAVE, sig, WaveType, ParVal, QMF, LD
;		IDL> tt = 'S' if 1D dataset or tt = 'I' if 2D dataset
;		IDL> ;Detrend dataset
;		IDL> sig = WDETREND(sig, tt)
;		IDL> See the detrended data
;		IDL> If tt EQ 'S' then WPLOTIT, st, 1, sig ELSE WPLOTIT, st, 10, sig
;
;MODIFICATION HISTORY:
;	Amara Graps September 1995.
;   copyright (c) Amara Graps 1995, 1996.
;-


TT = WSIGTYPE(sig, len, error)

CASE error OF
	1: BEGIN
		;Valid array or matrix
	
		CASE TT OF
			'I': BEGIN
				;byte image..detrend row by row
				pval = BYTARR(len, len)		;initialize pval
				FOR ix = 0, len-1 DO BEGIN
					row = sig(*, ix)
					indx = BINDGEN(len)
					pfit = POLY_FIT(indx,row,1)  ;fit poly of order 1 (get coeffs)
					;Evaluate terms using coefficients
					pval(*,ix) = POLY(indx, pfit)
					END	;end				
				END
			'S': BEGIN
				;signal
				x = FINDGEN(len)
				pfit = POLY_FIT(x, sig, 1)	;fit poly of order 1 (get coeffs)
				;Evaluate terms using coefficients
				pval = POLY(x, pfit)
				END				
		ENDCASE	;TT	
		END	;valid array or matrix
		
	ELSE: PRINT, 'Not valid data/signal array or matrix!'

ENDCASE		;error

;Remove linear trend
sig = sig - pval		



RETURN, sig
END		;of function wdetrend.pro