[GRASS-SVN] r45160 - grass-addons/raster/r.stream.order

[svn_grass at osgeo.org]

Author: hamish
Date: 2011-01-22 15:29:42 -0800 (Sat, 22 Jan 2011)
New Revision: 45160

Modified:
   grass-addons/raster/r.stream.order/description.html
Log:
typo

Modified: grass-addons/raster/r.stream.order/description.html
===================================================================
--- grass-addons/raster/r.stream.order/description.html	2011-01-22 22:57:33 UTC (rev 45159)
+++ grass-addons/raster/r.stream.order/description.html	2011-01-22 23:29:42 UTC (rev 45160)
@@ -63,7 +63,7 @@
  Strahler's stream order has a good mathematical background. All catchments with streams in this context are directed graphs, oriented from the root towards the leaves. Equivalent definition of the Strahler number of a tree is that it is the height of the largest complete binary tree that can be homeomorphically embedded into the given tree; the Strahler number of a node in a tree is equivalent to the height of the largest complete binary tree that can be embedded below that node. The disadvantage of that methods is the lack of distinguishing a main channel which may interfere with the analytical process in highly elongated catchments
 
 <H4>Horton's stream order</H4>
-Horton's stream order applies to the stream as a whole but not to segments or links since the order on any channel remains unchanged from source till it "dies" in the higher order stream or in the outlet of the catchment. The main segment of the catchment gets the order of the whole catchment, while its tributaries get the order of their own subcatchments. The main difficulties of the Horton's order are criteria to be considered to distinguish between "true" first order segments and extension of higher order segments. Thqat is the reason why Horton's ordering has rather historical sense and is substituted by the more unequivocal Strahler's ordering system. There are no natural algorithms to order stream network according to Horton' paradigm. The algorithm used in r.stream.order requires to first calculate Strahler's stream order (downstream) and next recalculate to Horton ordering (upstream). To make a decision about proper ordering it uses first Strahler ordering, and next,
  if both branches have the same orders it uses flow accumulation to choose the actual link. The algorithm starts with the outlet, where the outlet link is assigned the corresponding Strahler order. Next it goes upstream and determines links according to Strahler ordering. If the orders of tributaries differ, the algorithm proceeds with the channel of highest order, if all orders are the same, it chooses that one with higher flow length rate or higher catchment area if accumulation is used. When it reaches the initial channel it goes back to the last undetermined branch, assign its Strahler order as Horton order and goes upstream to the next initial links. In that way stream orders remain unchanged from the point where Horton's order have been determined to the source. 
+Horton's stream order applies to the stream as a whole but not to segments or links since the order on any channel remains unchanged from source till it "dies" in the higher order stream or in the outlet of the catchment. The main segment of the catchment gets the order of the whole catchment, while its tributaries get the order of their own subcatchments. The main difficulties of the Horton's order are criteria to be considered to distinguish between "true" first order segments and extension of higher order segments. That is the reason why Horton's ordering has rather historical sense and is substituted by the more unequivocal Strahler's ordering system. There are no natural algorithms to order stream network according to Horton' paradigm. The algorithm used in r.stream.order requires to first calculate Strahler's stream order (downstream) and next recalculate to Horton ordering (upstream). To make a decision about proper ordering it uses first Strahler ordering, and next, 
 if both branches have the same orders it uses flow accumulation to choose the actual link. The algorithm starts with the outlet, where the outlet link is assigned the corresponding Strahler order. Next it goes upstream and determines links according to Strahler ordering. If the orders of tributaries differ, the algorithm proceeds with the channel of highest order, if all orders are the same, it chooses that one with higher flow length rate or higher catchment area if accumulation is used. When it reaches the initial channel it goes back to the last undetermined branch, assign its Strahler order as Horton order and goes upstream to the next initial links. In that way stream orders remain unchanged from the point where Horton's order have been determined to the source. 
   
 <BR>
 <B>Advantages and disadvantages of Horton's ordering:</B>