Level Connector 1.0beta
Reads RAW or ASCII pgm file from stdin or from
file specified in command line and writes binary
pgm file to stdout.
The input is treated as height field and the
heights of pixels marked as free are calculated
so that different levels are connected smoothly.
The heights are found by solving Poisson's 2nd
order differential equation in the free areas
using modified Gauss-Seidel algorithm.
Gauss-Seidel iteration calculates approximations
for the [free] pixels based on previous values.
[Inithgt] is used as the first approximation. The
iteration stops when [maxiter] iterations are made
or maximum difference between iterations is less
than [limres]. If max difference reported by [stat]
is much greater than 1 it means that the approximation
is far from the final value and [maxiter] should be
increased. That is, if a better solution for the
Poisson's equation is desired.
If the input file contains no fixed areas inside
free areas then the approximations go towards
flat surface and [limres] should be set to 0.0.
The iteration is in this case controlled by
[maxiter] only.
[Force] pushes the free areas upwards. Values greater
than ~2 give unpredictable resuls. Negative force
pushes downwards.
If a pgm is generated using
> giftopnm foo.gif| ppmtopgm > foo.pgm
it may not preserve the original levels and some
guessing is required to find the right [free] value.
> giftoppm foo.gif| ppmtopgm > foo.pgm
works fine.
Remember to sort the colormap if you convert to gif.
Kari Kivisalo
kkivisal@vipunen.hut.fi
http://www.hut.fi/~kkivisal/
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