[GRASS-dev] Add a cost distance measure to GRASS GIS lib

[Benjamin Ducke]

> 
> Even cost along a straight line (or maybe a great circle?) is
> computationally expensive, and in the general case would require
> holding the entire cost map in memory. Less-general cases would have
> to be implemented within the module, as the libraries wouldn't know
> how the module intends to access the cost map.
> 
> Also, many algorithms which have a concept of distance require that it
> follows the conditions for a metric, i.e. for some metric d and all
> points x, y, z:
> 
> 	d(x,x) = 0
> 	d(x,y) >= 0
> 	d(x,y) = d(y,x)
> 	d(x,z) <= d(x,y) + d(y,z)
> 
> A distance calculated by integrating a cost map along a fixed path
> could violate the fourth condition (transitivity).
> 
> Other algorithms (e.g. r.grow.distance) require that distance
> increases monotonically with both delta-x and delta-y, and the
> proposed solution would violate that.
> 

Right, a general and simple solution for cost-based distance
is not as straight forward as I thought it might be.

I will think about how this could be done for individual
modules instead -- and which modules would actually
benefit significantly from cost distances.

Thanks for all the feedback.

Ben

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