diff --git a/src/mintpy/simulation/iono.py b/src/mintpy/simulation/iono.py
index 697fbd983..6557882fa 100644
--- a/src/mintpy/simulation/iono.py
+++ b/src/mintpy/simulation/iono.py
@@ -198,7 +198,7 @@ def incidence_angle_ground2iono(inc_angle, iono_height=450e3):
 def lalo_ground2iono(lat, lon, inc_angle, az_angle=None, head_angle=None, iono_height=450e3, method='spherical_distance'):
     """Calculate lat/lon of IPP with the given lat/lon on the ground and LOS geometry
 
-    Equation (12) in Yunjun et al. (2021, TGRS).
+    Equation (12) in Yunjun et al. (2022, TGRS).
 
     Parameters: lat/lon      - float, latitude/longitude of the point on the ground in degrees
                 inc_angle    - float/np.ndarray, incidence angle of the line-of-sight vector on the ground in degrees
diff --git a/src/mintpy/tsview.py b/src/mintpy/tsview.py
index 61163dfec..f010a2621 100644
--- a/src/mintpy/tsview.py
+++ b/src/mintpy/tsview.py
@@ -160,10 +160,13 @@ def read_init_info(inps):
     if not inps.ref_yx and 'REF_Y' in atr.keys():
         inps.ref_yx = (int(atr['REF_Y']), int(atr['REF_X']))
 
-    # ref_yx --> ref_lalo if in geo-coord
-    # for plotting purpose only
-    if inps.ref_yx and 'Y_FIRST' in atr.keys():
-        inps.ref_lalo = inps.coord.radar2geo(inps.ref_yx[0], inps.ref_yx[1], print_msg=False)[0:2]
+    # print/plot ref_yx/lalo info
+    if inps.ref_yx:
+        vprint(f'reference point in y/x: {inps.ref_yx}')
+        # ref_yx --> ref_lalo if in geo-coord [for plotting purpose only]
+        if 'Y_FIRST' in atr.keys():
+            inps.ref_lalo = inps.coord.radar2geo(inps.ref_yx[0], inps.ref_yx[1], print_msg=False)[0:2]
+            vprint(f'reference point in lat/lon: {inps.ref_lalo}')
 
     # do not plot native reference point if it's out of the coverage due to subset
     if (inps.ref_yx and 'Y_FIRST' in atr.keys()
@@ -171,7 +174,7 @@ def read_init_info(inps):
         and not (    inps.pix_box[0] <= inps.ref_yx[1] < inps.pix_box[2]
                  and inps.pix_box[1] <= inps.ref_yx[0] < inps.pix_box[3])):
         inps.disp_ref_pixel = False
-        print('the native REF_Y/X is out of subset box, thus do not display')
+        vprint('the native REF_Y/X is out of subset box, thus do not display')
 
     ## initial pixel coord
     if inps.lalo:
diff --git a/src/mintpy/utils/map.py b/src/mintpy/utils/map.py
index db49e7af7..4e4fb6355 100644
--- a/src/mintpy/utils/map.py
+++ b/src/mintpy/utils/map.py
@@ -77,6 +77,11 @@ def auto_lalo_sequence(geo_box, lalo_step=None, lalo_max_num=4, step_candidate=[
     Example:    geo_box = (128.0, 37.0, 138.0, 30.0)
                 lats, lons, step = m.auto_lalo_sequence(geo_box)
     """
+    # check input arguments
+    if geo_box[1] <= geo_box[3] or geo_box[2] < geo_box[0]:
+        raise ValueError(f'Input geo_box {geo_box} has N <= S or E <= W! Check the order of (W, N, E, S).')
+    if lalo_step and lalo_step <= 0:
+        raise ValueError(f'Input lalo_step ({lalo_step}) must be positive!')
 
     max_lalo_dist = max([geo_box[1] - geo_box[3], geo_box[2] - geo_box[0]])