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documentation/lagrit_manual/commands/kdtree.txt

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+.. _kdtree:
+
+****&nbsp_place_holder;
+
+> **_KDTREE&nbsp_place_holder;_**
+
+>
+
+>> **KDTRE**E uses the elements of the current mesh object to produce a k-D
+tree that is stored in the attributes LINKT and SBOX that are appended to the
+mesh object.&nbsp_place_holder; Leaf nodes in LINKT each contain exactly one
+element index.&nbsp_place_holder;&nbsp_place_holder; Because of the
+possibility of triangle overlap, **KDTREE** also produces an array SBOX which
+gives 'safety boxes'.&nbsp_place_holder; For each node in the k-D tree, there
+is a corresponding safety box which is just big enough to contain all the
+triangles&nbsp_place_holder; "under" the node.&nbsp_place_holder; The
+attributes LINKT and SBOX are used by the subroutine:&nbsp_place_holder;
+RETRIEVE_WITHIN_EPS.&nbsp_place_holder; RETRIEVE_WITHIN_EPS finds all elements
+with epsilon of the query point (xq,yq,zq). What is actually returned is a
+small subset of leaves&nbsp_place_holder; (i.e., elements) that feasibly could
+be within epsilon of the query point.&nbsp_place_holder; The user must then do
+exact geometric tests on this small subset to actually determine which
+elements are a distance epsilon from the query point.
+
+&nbsp_place_holder;
+
+>>
+
+>> subroutine retrieve_within_eps(xq,yq,zq,linkt,sbox,
+eps,nefound,iefound,ierr)
+
+> > xq, yq, zq&nbsp_place_holder;
+
+>> coordinates of query point
+
+>>
+
+>> linkt, sbox
+
+>> mesh object KDTREE attributes created by the KDTREE command
+
+>>
+
+>> eps&nbsp_place_holder;
+
+>> search epsilon
+
+>>
+
+>> nefound&nbsp_place_holder;
+
+>> number of elements found
+
+>>
+
+>> iefound
+
+>> array of elements found
+
+>>
+
+>> ierr
+
+>> error flag&nbsp_place_holder;&nbsp_place_holder; (0 = no error)
+
+>> &nbsp_place_holder;
+
+The attributes LINKT and SBOX may also be used by the subroutine:
+NEARESTPOINT.&nbsp_place_holder; NEARESTPOINT uses the k-D tree structure for
+a triangular surface mesh object&nbsp_place_holder; (generated by KDTREE) to
+accelerate finding the nearest point on the surface to the given query point
+(xq,yq,zq).&nbsp_place_holder; What is actually returned is a small subset of
+leaves (i.e., triangles) that feasibly could contain the nearest
+point.&nbsp_place_holder; The user must then do exact geometric tests on this
+small subset to determine points of intersection.
+
+&nbsp_place_holder;
+
+&nbsp_place_holder;subroutine nearestpoint(xq,yq,zq,xic,yic,zic,itet,xs,ys,zs,
+linkt,sbox,eps,distpossleaf,mtfound,itfound,ierr)
+
+&nbsp_place_holder;
+
+>>
+
+>> xq, yq, zq&nbsp_place_holder;
+
+>> coordinates of query point
+
+>>
+
+>> xic,yic,zic
+
+>> arrays of coordinates of nodes in the surface mesh object
+
+>>
+
+>> itet
+
+>> array containing trianged-node relationship for surface mesh object.
+
+>>
+
+>> xs,ys,zs
+
+>> coordinates of previous retrieved "nearestpoint".&nbsp_place_holder; If
+there is no previous query, set these to a very large value
+
+>>
+
+>> linkt, sbox
+
+>> mesh object.&nbsp_place_holder; KDTREE attributes created by the KDTREE
+command
+
+>>
+
+>> distpossleaf
+
+>> work array of length = number of triangles in the surface mesh.
+
+>>
+
+>> mtfound
+
+>> number of triangles found
+
+>>
+
+>> itfound
+
+>> array of triangle (element number) found
+
+>>
+
+>> ierr
+
+>> error flag
+
+>> &nbsp_place_holder;
+
+&nbsp_place_holder;
+
+>
+
+> &nbsp_place_holder;
+
+&nbsp_place_holder;
+
+>
+
+>> &nbsp_place_holder;
+
+&nbsp_place_holder;
+
+&nbsp_place_holder;
+
+&nbsp_place_holder;
+