extractPts: Extract ocean data values from a satin object

In satin: Visualisation and Analysis of Ocean Data Derived from Satellites

Extract ocean data values from a satin object

Description

Extract data values for pixels selected from an image of a satin object.

Usage

extractPts(X, points = NULL)

Arguments

X	a satin object as returned by read.nasaoc, read.ghrsst, read.osunpp, or read.cmems.
points	a data frame with point(s) longitude and latitude coordinates where to extract data values.

Details

If provided, points must have two columns with x and y coordinates. When not specified, points can be selected by clicking on the image. Note that for selecting the points in this manner, the plot of the satin object has to be created using colbar = FALSE.

Value

A data frame with at least 7 columns: For each point, a sequential id number; (x, y) coordinates, either specified via the points argument or selected by clicking on the image; (lon and lat) coordinates of pixels closer to the desired points; and for quality control purposes, the distance between them (d, km). The remaining column(s) are the parameter values for every image in the satin object.

Author(s)

Héctor Villalobos

Examples

# load data, define coordinates and extract values
data(dsst)

plot(dsst)
coord <- data.frame(x = seq(-130, -114, 2), y = seq(20, 36, 2))
values <- extractPts(dsst, points = coord)
values

# if no points are given the user can select them by clicking on the image
if (interactive()){
plot(dsst, colbar = FALSE)
values2 <- extractPts(dsst) # *** click on the image ***
values2
}

satin documentation built on Sept. 23, 2022, 1:06 a.m.