[GRASS-user] r.flow Terminates With Error

[Micha Silver]

Rich Shepard wrote:

> On Sat, 13 Feb 2010, Markus Neteler wrote:
>
>> Did you compile with LFS (large file support) enabled?
>
> Markus,
>
>   Yes. This came up before and Glynn ensured that LFS was enabled in my
> build.
>
>   In general, is there a way to predict memory and disk space 
> requirements
> before initiating processing?
In GRASS 6.5, Markus Metz has implemented a new r.watershed which is 
much faster as also handles memory better, (and also can do Multi Flow 
Direction analysis).
In his manual it says:
--------------quote---------------------
In-memory mode and disk swap mode
There are two versions of this program: ram and seg. ram is used by 
default, seg can be used by setting the -m flag.
The ram version requires a maximum of 31 MB of RAM for 1 million cells. 
Together with the amount of system memory (RAM) available, this value 
can be used to estimate whether the current region can be processed with 
the ram version.
The ram version uses virtual memory managed by the operating system to 
store all the data structures and is faster than the seg version; seg 
uses the GRASS segmentation library which manages data in disk files. 
seg uses only as much system memory (RAM) as specified with the memory 
option, allowing other processes to operate on the same system, even 
when the current geographic region is huge.
Due to memory requirements of both programs, it is quite easy to run out 
of memory when working with huge map regions. If the ram version runs 
out of memory and the resolution size of the current geographic region 
cannot be increased, either more memory needs to be added to the 
computer, or the swap space size needs to be increased. If seg runs out 
of memory, additional disk space needs to be freed up for the program to 
run. The r.terraflow module was specifically designed with huge regions 
in mind and may be useful here as an alternative.
--------------quote---------------------
I'll bet that the numbers above for memory requirements also would apply 
to GRASS 6.4

-- 
Micha

>
>   What I wanted to do (but will back off doing for valid time constraint
> reasons) was to improve the resolution of the DEM from 5m because one 
> of the
> modules I wanted to explore recommended a grid resolution in centimeters
> (much too fine for my needs). I tried r.resamp.rst to create 1m 
> results, but
> temporary file sizes were excessively large. Next I tried 3m, but it 
> turns
> out that r.flow cannot calculate the flow density map despite the 
> available
> memory and swap space. So, I'll stick with 5m resolution.
>
> Rich
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