diff --git a/libs/geom/include/psemek/geom/interval.hpp b/libs/geom/include/psemek/geom/interval.hpp
index bfc3c328..461733d3 100644
--- a/libs/geom/include/psemek/geom/interval.hpp
+++ b/libs/geom/include/psemek/geom/interval.hpp
@@ -232,6 +232,12 @@ namespace psemek::geom
 		return std::max(i.min, std::min(i.max, x));
 	}
 
+	template <typename T>
+	T lerp(interval<T> const & i, T t)
+	{
+		return i.min + i.length() * t;
+	}
+
 	template <typename Stream, typename T>
 	Stream & operator << (Stream & os, interval<T> const & i)
 	{