Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: New efficient methods to calculate watersheds   We present an advanced algorithm for the determination of watershed lines on
Digital Elevation Models (DEMs), which is based on the iterative application of
Invasion Percolation (IIP). The main advantage of our method over previosly
proposed ones is that it has a sub-linear time-complexity. This enables us to
process systems comprised of up to 10^8 sites in a few cpu seconds. Using our
algorithm we are able to demonstrate, convincingly and with high accuracy, the
fractal character of watershed lines. We find the fractal dimension of
watersheds to be Df = 1.211 +/- 0.001 for artificial landscapes, Df = 1.10 +/-
0.01 for the Alpes and Df = 1.11 +/- 0.01 for the Himalaya.

18
The categories of this paper are: econ
2
The categories of this paper are: math
32
The categories of this paper are: atom-ph
24
The categories of this paper are: dg-ga
27
The categories of this paper are: comp-gas
12
The categories of this paper are: nucl-th
22
The categories of this paper are: chao-dyn
13
The categories of this paper are: quant-ph
8
The categories of this paper are: hep-ex
3
The categories of this paper are: physics
6
The categories of this paper are: astro-ph
36
The categories of this paper are: cmp-lg
17
The categories of this paper are: q-fin
34
The categories of this paper are: chem-ph
33
The categories of this paper are: plasm-ph
15
The categories of this paper are: nucl-ex