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+.help lintran Apr84 lists
+.ih
+NAME
+lintran -- perform a linear transformation of a list
+.ih
+USAGE
+lintran files
+.ih
+PARAMETERS
+.ls files
+List file or files to be transformed.
+.le
+.ls xfield = 1, yfield = 2
+Fields containing the x and y coordinates.
+.le
+.ls x1 = 0.0, y1 = 0.0
+Coordinates of current origin.
+.le
+.ls xscale = 1.0, yscale = 1.0
+Scale factor to be applied to the input coordinates, relative
+to the current origin [x1,y1].
+.le
+.ls angle = 0.0
+Rotation angle about the origin [x1,y1].  This angle, measured
+counter clockwise from the positive x axis, is entered in
+degrees, unless \fBradians\fR = yes.
+.le
+.ls x2 = 0.0, y2 = 0.0
+Coordinates of the new origin; input coordinates are shifted by an 
+amount (x2-x1) and (y2-y1).  Positive shifts indicate increasing distance
+from the current origin.  Applied after scaling and rotating the input 
+coordinates.
+.le
+.ls radians = no
+If this parameter is set to yes, \fBangle\fR is input
+in radians, not degrees.
+.le
+.ls min_sigdigits = 1
+The number of significant digits to be output in the transformed fields 
+is the maximum of this parameter and the number of input significant digits. 
+.le
+.ih
+DESCRIPTION
+Specified fields from the input list can be scaled, rotated and shifted.
+Two fields of each input line are designated
+as the x and y coordinates to be transformed (default: fields 1, 2).
+All other fields are be preserved across the transformation.  
+For clarification, the equations used in the transformation are shown below:
+
+.ks
+.nf
+	1. Subtract off the current origin:
+    
+    	xt = x - x1
+    	yt = y - y1
+
+	2. Scale and rotate the coordinates:
+    
+	xs = xt * xscale
+	ys = yt * yscale
+    	xt = xs * cos(angle) - ys * sin(angle)
+    	yt = xs * sin(angle) + ys * cos(angle)
+
+	3. Shift to the new origin:
+
+	xt = xt + x2
+	yt = yt + y2
+.fi
+.ke
+
+Comment lines and blank lines are passed on to the output unmodified
+(a comment line is any line beginning with the character '#').
+If either x or y is indefinite
+and no rotation is being performed, the corresponding
+output coordinate will be indefinite.  If either input coordinate is indefinite
+and a rotation is being performed, both output coordinates will be indefinite.
+.ih
+EXAMPLES
+1. Shift the coordinate list frame1 so it represents positions
+in a second exposure of a star field, not registered with the first.  Take
+the coordinates of a star in frame1 to be the current origin 
+(e.g., [35.7, 389.2]); the new origin is then the coordinates of the same
+star in the second exposure ([36.9, 400.0]).  The shifted list is saved in
+file "frame2":
+
+    cl> lintran frame1 x1=35.7 y1=389.2 x2=36.9 y2=400.0 > frame2
+
+2. Apply a shift of +3.4 units in x, -1.3 units in y to the input list
+read from the standard input, writing the output list on the standard
+output.  
+
+    cl> list_stream | lintran x2=3.4 y2=-1.3
+
+3. Rotate a coordinate list of a 800x800 frame by 90 degrees.  The
+rotated coordinate list would represent positions in the field if it had
+been rotated, for example, from East to the right to East to the top.  
+Note that the rotation takes place about the central pixel [400.50,400.50]
+and that the current and new origins are the same:
+
+    cl> lintran picture x1=400.5 y1=400.5 x2=400.5 y2=400.5 angle=90
+.ih
+SEE ALSO
+.endhelp