Index: trunk/stac/src/stacTransform.c
===================================================================
--- trunk/stac/src/stacTransform.c	(revision 2500)
+++ trunk/stac/src/stacTransform.c	(revision 2661)
@@ -20,5 +20,5 @@
 						   unsigned int maskVal,
 						   psF64 unexposedValue)
-{ 
+{
     double floorX = floor((psF64)(x) - 0.5); 
     double floorY = floor((psF64)(y) - 0.5); 
@@ -206,10 +206,11 @@
 		(void)psPlaneTransformApply(detector, map, sky);
 
-		outImage->data.F32[y][x] = (psF32)psImagePixelInterpolate(image, detector->x, detector->y,
-									  mask, 1, 0.0,
+		outImage->data.F32[y][x] = (psF32)psImagePixelInterpolate(image, detector->x + 0.5,
+									  detector->y + 0.5, mask, 1, 0.0,
 									  PS_INTERPOLATE_BILINEAR);
-		outError->data.F32[y][x] = (psF32)p_psImageErrorInterpolateBILINEAR_F32(error, detector->x,
-											detector->y, mask, 1,
-											0.0);
+		outError->data.F32[y][x] = (psF32)p_psImageErrorInterpolateBILINEAR_F32(error,
+											detector->x + 0.5,
+											detector->y + 0.5,
+											mask, 1, 0.0);
 		outError->data.F32[y][x] = sqrtf(outError->data.F32[y][x]);
 	    }