diff --git a/src/ruby/mask_data.rb b/src/ruby/mask_data.rb
index 7f4789d..8dcb496 100644
--- a/src/ruby/mask_data.rb
+++ b/src/ruby/mask_data.rb
@@ -318,11 +318,9 @@ def produce_geom(xy, z, into, through, on, taper, bias, mode, buried, method)
       end
   
       d &= RBA::Region::new(into_data)
-      
-      poly = []
-      d.each { |p| poly << p }
-      return poly
-  
+
+      # Keep polygons touching the surface
+      return d.interacting(me).each.collect { |p| p }
     end
 
     # Computes the convolution of the edge sequence with the kernel