[R-sig-Geo] gdistance: working with vector speed data in two direction

[tf at devmag.net]

Dear all,

I have the following problem.

I managed to use the gdistance package to give me computations for  
shortest distances between two ocean points. I am working on a simple  
1 degree grid for that and it works fine.

However, now I want to incorporate something slightly more advanced.  
For each cell of the grid I have a wind vector with its horizontal and  
its vertical wind component; the units are speeds in meters per  
second, which can be positive / negative indicating the direction  
north/ south, east and west.

I have both of them as a raster object.

Similar to the vignette hiking example, I want to compute the fastest  
way to get from A to B. Imagine that the object that moves from A to B  
is a sailing boat that wants to exploit the best possible combiantion  
of winds along all possible paths from A to B.

The data structure for now is as follows:

vertical <- raster(nrows=10, ncols=10)
vertical <- setValues(vertical, runif(10*10, min=-1, max=1) )
horizontal <- raster(nrows=10, ncols=10)
horizontal <- setValues(horizontal, runif(10*10, min=-1, max=1) )

In the hiking example, the direction was either going up or going down  
which was captured by the sign of the height difference (i.e. the  
slope).

They key difference here is, that I essentially have "two signs" for  
both speed direction components.


I am not sure whether this is possible using the gdistance package; I  
would be happy to hear your thoughts and comments.

Best,
Thiemo