diff --git a/ObservationSim/ObservationSim.py b/ObservationSim/ObservationSim.py
index d80b0dc1f1a5799ec7ef7d3b9bc228955c291c28..5e79ec38bb51437f32599d6fce48a53d1129bc7a 100755
--- a/ObservationSim/ObservationSim.py
+++ b/ObservationSim/ObservationSim.py
@@ -258,11 +258,11 @@ class Observation(object):
                     raise ValueError("Unknown shear input")
                 
                 # chip_output.logger.info("debug point #4")
-                h_ext = generateExtensionHeader(
+                header_wcs = generateExtensionHeader(
                     xlen=chip.npix_x,
                     ylen=chip.npix_y,
-                    ra=pointing.ra,
-                    dec=pointing.dec,
+                    ra=ra_cen,
+                    dec=dec_cen,
                     pa=pointing.img_pa.deg,
                     gain=chip.gain,
                     readout=chip.read_noise,
@@ -273,7 +273,7 @@ class Observation(object):
                     col_num=chip.colID,
                     extName='raw')
 
-                pos_img, offset, local_wcs, real_wcs = obj.getPosImg_Offset_WCS(img=chip.img, fdmodel=self.fd_model, chip=chip, verbose=False, img_header=h_ext)
+                pos_img, offset, local_wcs, real_wcs = obj.getPosImg_Offset_WCS(img=chip.img, fdmodel=self.fd_model, chip=chip, verbose=False, img_header=header_wcs)
                 if pos_img.x == -1 or pos_img.y == -1:
                     # Exclude object which is outside the chip area (after field distortion)
                     # print("obj missed!!")