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diff --git a/pkg/plot/crtpict/xyscale.x b/pkg/plot/crtpict/xyscale.x
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+# Copyright(c) 1986 Association of Universities for Research in Astronomy Inc.
+
+include <mach.h>
+include <imhdr.h>
+include	<error.h>
+include	"wdes.h"
+include	"crtpict.h"
+
+# CRT_XY_SCALE -- Calculate the spatial transformation parameters and store
+# them in the "wdes" window descriptor.  These are used to map the image
+# to the graphics device.
+
+procedure crt_xy_scale (gp, cl, im, wdes)
+
+pointer	gp
+pointer	cl
+pointer	im
+pointer	wdes
+
+int	w1, w0, ndev_rows, ndev_cols
+real	xcenter, ycenter, xsize, ysize, pxsize, pysize, xscale, yscale
+real	ystart, yend
+int	ggeti()
+errchk	ggeti
+
+begin
+	ndev_rows = ggeti (gp, "yr")
+	ndev_cols = ggeti (gp, "xr")
+
+	# Determine the maximum display window available for mapping the
+	# image.  This is a function of the user specified "fractions";
+	# the outer 6% of the user specified image area is used for annotation.
+
+	xcenter = (CRT_XE + CRT_XS) / 2.0
+	xsize   = CRT_XE - CRT_XS
+	ystart  = CRT_YS + (CRT_YE - CRT_YS) * GRAPHICS_FRACTION(cl)
+	yend    = ystart + (CRT_YE - CRT_YS) * IMAGE_FRACTION(cl)
+	ycenter = (yend + ystart) / 2.0
+	ysize   = yend - ystart
+
+	# Set device window limits in normalized device coordinates.
+	# World coord system 0 is used for the device window.
+
+	w0 = W_WC(wdes,0)
+	W_XS(w0) = xcenter - (xsize / 2.0)
+	W_XE(w0) = xcenter + (xsize / 2.0)
+	W_YS(w0) = ycenter - (ysize / 2.0)
+	W_YE(w0) = ycenter + (ysize / 2.0)
+
+	# Determine X and Y scaling ratios required to map the image into the
+	# normalized display window.  
+
+	if (FILL(cl) == YES) {
+	    # Compute scale in units of NDC viewport coords per image pixel.
+	    xscale = xsize / max (1, (IM_LEN(im,1) - 1))
+	    yscale = ysize / max (1, (IM_LEN(im,2) - 1))
+
+	    # Image scaled by same factor in x and y with FILL = YES.
+	    if (xscale < yscale)
+		yscale = xscale
+	    else
+		xscale = yscale
+
+	} else {
+	    # From the user specified magnification factors, compute the scale
+	    # in units of NDC coords per "effective" display pixels.
+
+	    xscale = 1.0 / ((ndev_cols - 1) / XMAG(cl))
+	    yscale = 1.0 / ((ndev_rows - 1) / YMAG(cl))
+	}
+
+	# Determine the image pixels that map to the available device
+	# viewport.  The starting and ending pixels calculated from
+	# xscale and yscale may be in the image interior or reference 
+	# beyond the bounds of the image.  These endpoints are tuned
+	# further in procedure transform_image.
+
+	w1 = W_WC(wdes,1)
+	pxsize = xsize / xscale
+	pysize = ysize / yscale
+
+	W_XS(w1) = (IM_LEN(im,1) - 1) / 2.0 + 1 - (pxsize / 2.0)
+	W_XE(w1) = W_XS(w1) + pxsize
+	W_YS(w1) = (IM_LEN(im,2) - 1) / 2.0 + 1 - (pysize / 2.0)
+	W_YE(w1) = W_YS(w1) + pysize
+
+	# All spatial transformations are linear.
+	W_XT(w1) = W_LINEAR
+	W_YT(w1) = W_LINEAR
+end