From 4c004afd33286adf8053323ed502610eff4e3044 Mon Sep 17 00:00:00 2001
From: Liangliang Zhang <zhangliangliang@baidu.com>
Date: Mon, 17 Sep 2018 20:31:42 -0700
Subject: [PATCH] Control: fixed a bug in control.

---
 modules/control/common/interpolation_2d.cc | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/modules/control/common/interpolation_2d.cc b/modules/control/common/interpolation_2d.cc
index 9bc13f2926..d572e9c95d 100644
--- a/modules/control/common/interpolation_2d.cc
+++ b/modules/control/common/interpolation_2d.cc
@@ -52,7 +52,9 @@ double Interpolation2D::Interpolate(const KeyType &xy) const {
 
   auto itr_after = xyz_.lower_bound(xy.first);
   auto itr_before = itr_after;
-  --itr_before;
+  if (itr_before != xyz_.begin()) {
+    --itr_before;
+  }
 
   double x_before = itr_before->first;
   double z_before = InterpolateYz(itr_before->second, xy.second);
-- 
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