Message-ID: <72e8303a0712021231q64140d5t6a18d52684753fc7@mail.gmail.com>
Date: 2007-12-02T20:31:39Z
From: Dale Steele
Subject: How to find ocean depth at specific locations?
I would like to use ocean depth as a covariate in a spatial model
where I have a measured catch at a specific location, but depth at
that site was not reported in the original dataset. The dataset
'scallop' in package SemiPar is a representative example:
> scallop[20:25,]
latitude longitude tot.catch
20 39.46667 -72.66667 722
21 39.43333 -72.73333 41
22 39.40000 -72.80000 39
23 39.31667 -72.73333 0
24 39.33333 -72.85000 94
25 39.26667 -72.81667 7
I've been able to download a very large grid of depths in this area
(33514 points) from: <http://topex.ucsd.edu/cgi-bin/get_data.cgi>.
Given this data, I'm stuck at how to estimate the depth at each
location in the scallops dataset.
depths <- read.table("depths.txt", header=F,col.names=c("x","y","z"))
depths$x <- depths$x - 360
## subset the data keeping only negative depths
depths <- subset(depths, depths$z < 0)
## Convert depths to a positive number
depths$z <- (-1)*depths$z
length(depths$z)
Thanks. --Dale