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Posted by PJ Halls on March 6, 2007, 8:44 am
Please log in for more thread options image wrote:
> Paul Cooper ha scritto:
>
>
>>
>>
>>>Hello,
>>>I studying for final examination at the University about a area with
>>>very hight
>>>risk hydrological. The area studied is about 58 Km square, and it's
>>>very
>>>level surface, moreover, the area is under sea level. I have applied
>>>all must the algorithms, for example: for accumulation point, flow
>>>direction, pour point ecc. But, the area is too much level, and there
>>>are no result for this research. how can I discover the accumulation
>>>point?
>>>thanks You Paolo Ceddia.
>>
>>It sounds as if your data are not good enough for the analysis you
>>want to perform. You would need a very high accuracy DEM (e.g. created
>>by a LIDAR system) to get good results in a region such as you
>>describe. Contour data are simply not up to the job.
>>
>>Paul Cooper
>
>
> Yes, my date very definite, is a liDar 1x1 in plane and about 0.15 m
> in elevation, but the original is over 30000 pulse for Ha . I have
> used the standards the algorithms of esri and erMapper, but notting.
> how can looking for the accumulation ecc. How can I discover a
> algorithm to improve? how can I applied this algorithm in arcGis (can
> I specified in raster calculator)?
> very very thanks
>
Given your data volume, you might be advised to explore the ArcGIS
Workstation product. It's command line, rather than menus, but it is
easier to do the grid algebra there than in raster calculator (my
students keep telling me!). For your requirements, I would anticipate
creating one or more scripts (see ArcDoc, Customizing ArcInfo, AML) to
perform your analysis and then set the whole thing to run (and run and
run). You might find a Unix platform, if available, more reliable for
the sort of run length your data volumes will involve.
I'm not a hydrologist and so cannot recommend, but for the algorithmic
issues you need to seek out an appropriate textbook on hydrological
analysis ...
Alternatively, seek out a hydrological modelling tool, rather than seek
to do this in a GIS.
Peter
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