[GRASS-dev] Re: [GRASS-user] low radiance values after i.atcor and i.topo.corr

[Moritz Lennert]

On 21/06/08 14:24, Markus Neteler wrote:
> On Sat, Jun 21, 2008 at 1:47 PM, Glynn Clements
> <glynn at gclements.plus.com> wrote:
>> Markus Neteler wrote:
>>
>>>>>> Thanks!  Multiplying by 1000 with r.mapcalc gives better results.  Any
>>>>>> chance adding floating points (FCELL) to i.cluster?
>>>>> I had a brief look at the code[1], and cannot see any obvious reason
>>>>> why the values would need to be integers, so I'm assuming that it's
>>>>> just a legacy of the days before FP support was added.
>>>>>
>>>>> [1] Most of the code is actually in the lib/imagery/c_*.c files. That
>>>>> should either be made part of i.cluster (nothing else uses it), or at
>>>>> least split into a separate library.
>>>> I have committed these changes (splitting the cluster code off to a
>>>> separate library, and changing it to use DCELL instead of CELL) to the
>>>> SVN trunk.
>>>>
>>>> I would appreciate it if someone who understands i.cluster could test
>>>> the current version.
>>> (I have backported the changes to 6.4.svn for easier testing for me).
>>>
>>> The i.cluster continues to work for CELL maps.
>>>
>>> Here a test with the NC data set for FP maps:
>>> Maybe my example is nonsense?
>> Well, I don't actually understand what i.cluster does, so I couldn't
>> tell "sensible" output from garbage.
> 
> It does something like this:
> http://en.wikipedia.org/wiki/Cluster_analysis

More precisely it does a k-means style of cluster analysis, AFAICT. It 
is used in image classification to reduce the number of elements to 
class from the total of individual pixels to a more limited number of 
pixel clusters.


> What's needed since we cannot change the format is a normalization
> related to the range (AFAIK in i.cluster/print2.c).

After a rapid look: isn't the problem rather in lib/imagery/sig.c, 
function I_write_signatures, where the fprintf statements use a simple %f ?

Moritz