[GRASS-user] how to tweak the parameters to speed up i.segment

[Markus Metz]

On Fri, Sep 26, 2014 at 1:36 PM, Moritz Lennert
<mlennert at club.worldonline.be> wrote:
> On 26/09/14 11:56, Margherita Di Leo wrote:
>>
>> Hi,
>>
>> I have not clear understanding how the parameters
>
> [...]
>>
>> in i.segment could be tweaked to speed up the running time.
>
>> memory,
>
> This is probably the parameter you most want to play with. If you have
> lots of memory on the machine you can seriously increase this and this
> should normally speed up the process.

threshold is probably even more important than memory, because a
larger threshold value means longer running time. If you are not sure
which threshold value gives you the desired results (depends on your
data and your objective), you should start with a low value, e.g.
0.01, and then perform hierarchical segmentation by using the output
of the last run as seeds for the next run. Suggested steps are 0.01,
0.05, 0.1, 0.2. You could also test one or several small regions
within your study area before performing the real segmentation on the
full study area.

>
> More generally, segmentation is a time-consuming process. i.segment is
> already much faster than the proprietary market leader....

To be fair, this market leader offers some time consuming features
that are not implemented in i.segment.

Markus M