nestSearch: Finds the closest pixel center to a point

In frycast/rcosmo: Cosmic Microwave Background Data Analysis

Finds the closest pixel center to a point

Description

Finds the closest HEALPix pixel center to a given target point, specified in Cartesian coordinates, using an efficient nested search algorithm. HEALPix indices are all assumed to be in the "nested" ordering scheme.

Usage

nestSearch(target, nside, index.only = FALSE, save.dots = FALSE)

Arguments

target	A data.frame, matrix or vector of Cartesian (x,y,z) coordinates for the target point. If a data.frame is used then spherical coordinates can be specified with row names theta and phi.
nside	An integer, the target resolution at which the resulting pixels are returned.
index.only	A boolean indicating whether to return only the pixel index (TRUE), or cartesian coordinates as well (FALSE).
save.dots	A logical. A If TRUE then the dot product of each observation with the nearest child HEALPix pixel center will be returned as an attribute called "dot". Note that a 'child' pixel is any one of the four pixels contained in the current pixel in the nested scheme, at the next highest resolution. See children.

Value

if index.only = TRUE then the output will be a HEALPix index. If index.only FALSE then the output is the list containing the HEALPix index and Cartesian coordinate vector of the HEALPix point closest to target at resolution nside.

Examples

## Find the closest HEALPix pixel center at resolution j=2 for
## the point (0.6,0.8,0)

point <- c(0.6,0.8,0)
j <- 2
cpoint <- nestSearch(point, nside = 2^j)

## Plot the closest pixel center in blue and the point (0.6,0.8,0) in red
displayPixels(j, j, plot.j=j, spix=c(cpoint$pix),
              size=5, incl.labels =FALSE)
rgl::plot3d(point[1], point[2], point[3],
            col="red", size = 5, add = TRUE)


## Repeat the above for 4 points in a data.frame
points <- data.frame(x = c(1,0,0,0.6),
                     y = c(0,1,0,0.8),
                     z = c(0,0,1,0))
points
j <- 2
cpoints <- nestSearch(points, nside = 2^j)

## Plot the closest pixel center in blue and the point (0.6,0.8,0) in red
displayPixels(j, j, plot.j=j, spix=c(cpoints$pix),
              size=5, incl.labels =FALSE)
rgl::plot3d(points[,1], points[,2], points[,3],
            col="red", size = 5, add = TRUE)

frycast/rcosmo documentation built on Oct. 11, 2022, 5:21 p.m.