How to find ocean depth at specific locations?
Thank you very much. I think I've made progress, but am now stuck.... I now have two data frames (sample appended below). I would like to find the indices of 'Depth' on locations in 'Scallop' so I can add 'depth' as a covariate at each sample location in 'Scallop'. Two issues arise when I try code adapted from your example. 1) The code below generates an error message, when I try to find the indices of 'Depth' at locations in 'Scallop'.
overlay(Depth, Scallop)
Error in function (classes, fdef, mtable) :
unable to find an inherited method for function "overlay", for
signature "SpatialPointsDataFrame", "SpatialPointsDataFrame"
2) The code below first plots the points from Scallop, then draws
Depth (color image) which covers(obscures) the points drawn
previously.
spplot(Depth, "depth", sp.layout= list("sp.points", Scallop))
-
2) The code below generates an error message, when I try to find the
indices of 'Depth' at locations in 'Scallop'.
overlay(Depth, Scallop)
Error in function (classes, fdef, mtable) : unable to find an inherited method for function "overlay", for signature "SpatialPointsDataFrame", "SpatialPointsDataFrame"
Depth[1:5,]
coordinates depth 7 (593.212, 4539.22) 10 22 (614.239, 4539.51) 4 23 (615.643, 4539.53) 6 24 (617.048, 4539.56) 8 25 (618.444, 4539.58) 8
Scallop[1:5,]
coordinates tcatchp1 1 (792.142, 4494.53) 1 2 (795.331, 4485.39) 1 3 (778.164, 4490.29) 1 4 (767.395, 4475.07) 2 5 (773.325, 4467.87) 1 Thanks. --Dale
On Dec 2, 2007 4:26 PM, Paul Hiemstra <p.hiemstra at geo.uu.nl> wrote:
Hi Dale,
If you have all your data in Spatial objects (sp-package) and they are
both in the same projection you can use the overlay function. Read
?overlay for more info. Small example:
# Script to extract the distance to the river meuse (holland) from a
grid (meuse.grid) for the points in meuse.
library(sp)
data(meuse)
coordinates(meuse) =~x+y
data(meuse.grid)
gridded(meuse.grid) = ~x+y
spplot(meuse.grid, "dist", sp.layout = list("sp.points", meuse))
# Get indices of meuse.grid that contain the values of the grid at the
overlay(meuse.grid, meuse)
# Get the values from the grid and attach to meuse
meuse$new_dist = meuse.grid$dist[overlay(meuse.grid, meuse)]
hope this helps!
cheers,
Paul
Dale Steele schreef:
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
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-- Drs. Paul Hiemstra Department of Physical Geography Faculty of Geosciences University of Utrecht Heidelberglaan 2 P.O. Box 80.115 3508 TC Utrecht Phone: +31302535773 Fax: +31302531145 http://intamap.geo.uu.nl/~paul