verify that ing and egr (chord) gaps exist before checking if egress comes before ingress

Author: jfong001

rss_ringoccs/occgeo/calc_occ_geometry.py

@@ -866,8 +866,9 @@ def get_freespace(t_ret_spm_vals, year, doy, rho_km_vals,
         gaps_km = {'INGRESS': gaps_km_ing,
                 'EGRESS': gaps_km_egr}
         # Add ingress and egress freespace regions together
-        if gaps_spm_egr[0][0] < gaps_spm_ing[0][0]:
-            gaps_spm = gaps_spm_egr.tolist() + gaps_spm_ing.tolist()
+        if len(gaps_spm_egr)!=0 and len(gaps_spm_ing)!=0:
+            if gaps_spm_egr[0][0] < gaps_spm_ing[0][0]:
+                gaps_spm = gaps_spm_egr.tolist() + gaps_spm_ing.tolist()
         else:
             gaps_spm = gaps_spm_ing.tolist() + gaps_spm_egr.tolist()