Index: /issm/trunk-jpl/src/m/classes/mesh.py
===================================================================
--- /issm/trunk-jpl/src/m/classes/mesh.py	(revision 13992)
+++ /issm/trunk-jpl/src/m/classes/mesh.py	(revision 13993)
@@ -92,7 +92,7 @@
 		string="%s\n%s"%(string,fielddisplay(self,"vertexonsurface","upper vertices flags list"))
 		string="%s\n%s"%(string,fielddisplay(self,"elementonsurface","upper elements flags list"))
-		string="%s\n%s"%(string,fielddisplay(self,"uppervertex","upper vertex list (NaN for vertex on the upper surface)"))
+		string="%s\n%s"%(string,fielddisplay(self,"uppervertex","upper vertex list (-1 for vertex on the upper surface)"))
 		string="%s\n%s"%(string,fielddisplay(self,"upperelements","upper element list (NaN for element on the upper layer)"))
-		string="%s\n%s"%(string,fielddisplay(self,"lowervertex","lower vertex list (NaN for vertex on the lower surface)"))
+		string="%s\n%s"%(string,fielddisplay(self,"lowervertex","lower vertex list (-1 for vertex on the lower surface)"))
 		string="%s\n%s"%(string,fielddisplay(self,"lowerelements","lower element list (NaN for element on the lower layer)"))
 		string="%s\n%s"%(string,fielddisplay(self,"vertexonboundary","vertices on the boundary of the domain flag list"))
Index: /issm/trunk-jpl/src/m/classes/model/model.py
===================================================================
--- /issm/trunk-jpl/src/m/classes/model/model.py	(revision 13992)
+++ /issm/trunk-jpl/src/m/classes/model/model.py	(revision 13993)
@@ -291,10 +291,10 @@
 		if md1.mesh.dimension==3:
 			md2.mesh.uppervertex=md1.mesh.uppervertex[pos_node]
-			pos=numpy.nonzero(numpy.logical_not(numpy.isnan(md2.mesh.uppervertex)))[0]
-			md2.mesh.uppervertex[pos]=Pnode[md2.mesh.uppervertex[pos].astype(int)-1]
+			pos=numpy.nonzero(numpy.logical_not(md2.mesh.uppervertex==-1))[0]
+			md2.mesh.uppervertex[pos]=Pnode[md2.mesh.uppervertex[pos]-1]
 
 			md2.mesh.lowervertex=md1.mesh.lowervertex[pos_node]
-			pos=numpy.nonzero(numpy.logical_not(numpy.isnan(md2.mesh.lowervertex)))[0]
-			md2.mesh.lowervertex[pos]=Pnode[md2.mesh.lowervertex[pos].astype(int)-1]
+			pos=numpy.nonzero(numpy.logical_not(md2.mesh.lowervertex==-1))[0]
+			md2.mesh.lowervertex[pos]=Pnode[md2.mesh.lowervertex[pos]-1]
 
 			md2.mesh.upperelements=md1.mesh.upperelements[pos_elem]
@@ -538,6 +538,6 @@
 
 		#Keep a trace of lower and upper nodes
-		mesh.lowervertex=float('NaN')*numpy.ones(number_nodes3d)
-		mesh.uppervertex=float('NaN')*numpy.ones(number_nodes3d)
+		mesh.lowervertex=-1*numpy.ones(number_nodes3d,int)
+		mesh.uppervertex=-1*numpy.ones(number_nodes3d,int)
 		mesh.lowervertex[md.mesh.numberofvertices:]=numpy.arange(1,(numlayers-1)*md.mesh.numberofvertices+1)
 		mesh.uppervertex[:(numlayers-1)*md.mesh.numberofvertices]=numpy.arange(md.mesh.numberofvertices+1,number_nodes3d+1)