Tell me if I'm wrong, but I am guessing that you are trying to calculate the minimum distance between two points, given the presence of barriers between them. For this problem, I have been using cost distances. By giving a raster representing the cost of crossing one cell of the landscape, the minimum distance that minimises the cost of movement between two locations can be found. If you assign the cells of a projected raster that represent the sea with a value of 1, and the cells that represent land with a very high value (or infinite), the resulting cost distance will be the minimum distance over sea, without going over land.
I have been using GRASS for this, but cost distances can also be calculated in R with the gdistance package. But I don't have much experience with it. Cheers, -Yvan On 8 June 2014 18:00, jwd <j...@surewest.net> wrote: > On Thu, 5 Jun 2014 14:58:11 +0200 > Giulia Fassio <giuliafas...@gmail.com> wrote: > >> Hello, >> >> someone know if it is possible to use R to calculate distance by sea >> between two geographic coordinates? I have many points in the sea and >> I want to create a matrix using R of the length of trajectories that >> pass only trough sea. >> >> Thanks >> >> Giulia >> > > You need to be a great deal more detailed before you are likely to get > useful advice. Are you trying to track a sea mammal for example? Or > are you working out the course for a sea vessel to travel? > > JWDougehrty > > ______________________________________________ > R-help@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. -- Yvan Richard DRAGONFLY Science Physical address: Level 5, 158 Victoria St, Te Aro, Wellington Postal address: PO Box 27535, Wellington 6141 New Zealand Ph: 04.385.9285 web page ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
