[GRASS-user] curve sketching

[Glynn Clements]

Martin Wegmann wrote:

> I am looking for a function related to "curve sketching" (Kurvendiskussion in 
> german) - I think r.series would be the perfect place for it, but before 
> submitting a wish, I just wanted to ask if there already exists a module 
> which fullfills this task.
> 
> If would be very handy to have functions like:
> 
> - point of global maximum (already in r.series -> max_raster)
> - point of global minimum (already in r.series -> min_raster)
> - turning point  (Wendepunkt)
> - point of max./min. slope (e.g. growing season, senescence)
> - information about unimodal/bimodal etc. phenology (no idea how to add this)

Two problems which I see here:

1. The input to the aggregate is a series of discrete samples rather
than a curve. Of course, you can always fit a curve to the samples,
but there are an unlimited number of ways to do that, none of which is
the sole "correct" approach, and different approaches will typically
produce different results.

2. Some of these may have multiple values, e.g. a curve can have
multiple points of inflection in the same way that it can have
multiple local minima/maxima.

IOW, the problem isn't with implementation but with definition. Once
you've defined exactly what you wish to calculate, implementing it is
likely to be relatively straightforward.

-- 
Glynn Clements <glynn at gclements.plus.com>