update app.py

app.py

@@ -90,9 +90,8 @@ if main_selection:
 
 # Earth Engine Index Calculator Section
 st.header("Earth Engine Index Calculator")
-
 # Load band information based on selected dataset
-if main_selection and sub_selection:  # Now safe because sub_selection is initialized
+if main_selection and sub_selection:
     dataset_bands = data[main_selection]["bands"].get(sub_selection, [])
     st.write(f"Available Bands for {sub_options[sub_selection]}: {', '.join(dataset_bands)}")
 
@@ -114,21 +113,20 @@ if main_selection and sub_selection:  # Now safe because sub_selection is initia
 
     # Show custom formula input if bands are selected
     if selected_bands:
-        # Provide a default formula based on the number of selected bands
         if len(selected_bands) == 1:
             default_formula = f"{selected_bands[0]}"
             example = f"'{selected_bands[0]} * 2' or '{selected_bands[0]} + 1'"
-        else:  # len(selected_bands) == 2
+        else:
             default_formula = f"({selected_bands[0]} - {selected_bands[1]}) / ({selected_bands[0]} + {selected_bands[1]})"
             example = f"'{selected_bands[0]} * {selected_bands[1]} / 2' or '({selected_bands[0]} - {selected_bands[1]}) / ({selected_bands[0]} + {selected_bands[1]})'"
 
         custom_formula = st.text_input(
             "Enter Custom Formula",
             value=default_formula,
-            help=f"Use only these bands: {', '.join(selected_bands)}. Examples: {example}"
+            help=f"Use only these bands: {', '.join(selected_bands)}. Examples: {example}. Note: Actual band availability depends on the data."
         )
 
-        # Validate the formula
+        # Validate the formula syntax
         def validate_formula(formula, selected_bands):
             allowed_chars = set(" +-*/()0123456789.")
             terms = re.findall(r'[a-zA-Z][a-zA-Z0-9_]*', formula)
@@ -368,9 +366,13 @@ def calculate_custom_formula(image, geometry, selected_bands, custom_formula, re
         band_values = {}
         band_names = image.bandNames().getInfo()
         
+        # Check if all selected bands are available in the image
+        missing_bands = [band for band in selected_bands if band not in band_names]
+        if missing_bands:
+            st.warning(f"The following bands are not available in the dataset for this image: {', '.join(missing_bands)}. Available bands: {', '.join(band_names)}. Please adjust your formula or data selection.")
+            return ee.Image(0).rename('custom_result').set('error', f"Missing bands: {', '.join(missing_bands)}")
+
         for band in selected_bands:
-            if band not in band_names:
-                raise ValueError(f"Band '{band}' not found in the dataset.")
             band_values[band] = image.select(band)
 
         reducer = get_reducer(reducer_choice)
@@ -405,7 +407,7 @@ def calculate_custom_formula(image, geometry, selected_bands, custom_formula, re
     except Exception as e:
         st.error(f"Unexpected error: {e}")
         return ee.Image(0).rename('custom_result').set('error', str(e))
-
+        
 # Function to calculate index for a period
 def calculate_index_for_period(image, roi, selected_bands, custom_formula, reducer_choice):
     return calculate_custom_formula(image, roi, selected_bands, custom_formula, reducer_choice)