diff --git a/externals/libmath b/externals/libmath
index 551c5fd..6b5b07e 160000
--- a/externals/libmath
+++ b/externals/libmath
@@ -1 +1 @@
-Subproject commit 551c5fdbfd95b42d5d1049bc322c70cea6fa7b3c
+Subproject commit 6b5b07e2074d8faab044cd80b4f309c9b53a202e
diff --git a/externals/vts-libs b/externals/vts-libs
index f533edf..f5bff04 160000
--- a/externals/vts-libs
+++ b/externals/vts-libs
@@ -1 +1 @@
-Subproject commit f533edf55458ca2100cffcdb11af5c88c390a105
+Subproject commit f5bff04cde00ccb9cda5f57681cf9a535b036ffe
diff --git a/mapproxy/src/mapproxy/generator/metatile.cpp b/mapproxy/src/mapproxy/generator/metatile.cpp
index d564a50..55488da 100644
--- a/mapproxy/src/mapproxy/generator/metatile.cpp
+++ b/mapproxy/src/mapproxy/generator/metatile.cpp
@@ -70,10 +70,13 @@ struct Sample {
         , max(conv(math::Point3(x, y, value[2])))
         , heightRange(navConv(math::Point3(x, y, value[1]))(2)
                       , navConv(math::Point3(x, y, value[2]))(2))
-        , ge(geConv(math::Point3(x, y, value[1]))(2)
-             , geConv(math::Point3(x, y, value[2]))(2)
-             , geConv(math::Point3(x, y, value[0]))(2))
-    {}
+    {
+        // ge is invalid so far, update it with extremes
+        vts::update(ge, geConv(math::Point3(x, y, value[1])));
+        vts::update(ge, geConv(math::Point3(x, y, value[2])));
+        // set surrogate
+        ge.surrogate = geConv(math::Point3(x, y, value[0]))(2);
+    }
 };
 
 const Sample* getSample(const Sample &sample)
@@ -356,7 +359,7 @@ metatileFromDemImpl(const vts::TileId &tileId, Sink &sink, Arsenal &arsenal
 
                 // compute tile extents and height range
                 auto heightRange(HeightRange::emptyRange());
-                math::Extents3 te(math::InvalidExtents{});
+                // math::Extents3 te(math::InvalidExtents{});
                 double area(0.0);
                 int triangleCount(0);
                 double avgHeightSum(0.f);
@@ -373,8 +376,8 @@ metatileFromDemImpl(const vts::TileId &tileId, Sink &sink, Arsenal &arsenal
                         // update tile extents (if sample valid)
                         if (p) {
                             // update by both minimum and maximum
-                            math::update(te, p->min);
-                            math::update(te, p->max);
+                            // math::update(te, p->min);
+                            // math::update(te, p->max);
                             vts::update(node.geomExtents, p->ge);
                             avgHeightSum += p->ge.surrogate;
                             ++avgHeightCount;
@@ -403,7 +406,7 @@ metatileFromDemImpl(const vts::TileId &tileId, Sink &sink, Arsenal &arsenal
                 setChildren(block, nodeId, node);
 
                 // set extents
-                node.extents = vr::normalizedExtents(rf, te);
+                // node.extents = vr::normalizedExtents(rf, te);
 
                 // build height range
                 node.heightRange.min = std::floor(heightRange.min);
diff --git a/mapproxy/src/mapproxy/generator/surface-spheroid.cpp b/mapproxy/src/mapproxy/generator/surface-spheroid.cpp
index cca3afb..ea67892 100644
--- a/mapproxy/src/mapproxy/generator/surface-spheroid.cpp
+++ b/mapproxy/src/mapproxy/generator/surface-spheroid.cpp
@@ -368,7 +368,7 @@ void SurfaceSpheroid::generateMetatile(const vts::TileId &tileId
 
                 // compute tile extents and height range
                 auto heightRange(vs::Range<double>::emptyRange());
-                math::Extents3 te(math::InvalidExtents{});
+                // math::Extents3 te(math::InvalidExtents{});
                 double area(0);
                 int triangleCount(0);
                 double avgHeightSum(0.f);
@@ -383,14 +383,14 @@ void SurfaceSpheroid::generateMetatile(const vts::TileId &tileId
 
                         // update tile extents (if point valid)
                         if (p) {
-                            math::update(te, *p);
+                            // math::update(te, *p);
                             // convert point to proper SDS
-                            const auto sdsHeight(geConv(*p)[2]);
+                            const auto sdPoint(geConv(*p));
                             // update geom extents
-                            vts::update(node.geomExtents, sdsHeight);
+                            vts::update(node.geomExtents, sdPoint);
 
                             // accumulate average height (surrogate) calculator
-                            avgHeightSum += sdsHeight;
+                            avgHeightSum += sdPoint(2);
                             ++avgHeightCount;
                         }
 
@@ -424,7 +424,7 @@ void SurfaceSpheroid::generateMetatile(const vts::TileId &tileId
                 }
 
                 // set extents
-                node.extents = vr::normalizedExtents(rf, te);
+                // node.extents = vr::normalizedExtents(rf, te);
 
                 // build height range
                 node.heightRange.min = std::floor(heightRange.min);