radec.to.xy: RA/Dec to Pixel

In AngusWright/LAMBDAR: Measure galaxy fluxes from an arbitrary FITS image using input aperture locations and dimensions

RA/Dec to Pixel

Description

Maps a provided array of RAs and Decs to pixel locations X and Y using the TAN Gnomonic projection, when provided with calibrating central RA/Dec, X/Y, and scales.

Usage

radec.to.xy(ra, dec, ra0 = 0, dec0 = 0,
x0 = 0, y0 = 0, xscale = 1, yscale = 1)

Arguments

ra	numeric (n) vector; the (n) RAs to be converted (deg)
dec	numeric (n) vector; the (n) Decs to be converted (deg)
ra0	numeric; the RA at the calibrating pixel (deg)
dec0	numeric; the Dec at the calibrating pixel (deg)
x0	numeric; x-coordinate of the calibrating pixel
y0	numeric; x-coordinate of the calibrating pixel
xscale	numeric; RA-interval between successive x pixels (deg)
yscale	numeric; Dec-interval between successive y pixels (deg)

Value

numeric (n,2) array; two column bound vectors containing the desired x pixel locations [,'X'] and y pixel locations [,'Y']

Note

This function is called by the ad.to.xy function, which extracts relevant information from an astrometry data.frame internally. It is therefore often more convenient to call ad.to.xy rather than to call radec.to.xy directly.

Note

This function is designed to work with the TAN Gnomonic projection. However, due to degeneracy the procedure can also be used with a orthographic SIN projection *without rotation*.

Author(s)

Aaron Robotham ICRAR [e-mail]

Examples

#Load LAMBDAR
library(LAMBDAR)

#Load sample image
data(SDSS.sample)
#Load sample catalogue
data(ApCat.sample)
#Save sample image to File
write.fits(file="SampleImage.fits",SDSS.sample)
#Read Astrometry
astr<-read.astrometry("SampleImage.fits")
#Get the relevent parameters from the Astrometry Header
### NB: This snippet is within the ad.to.xy function, which is a
###     wrapper to the radec.to.xy function
ra0<-astr$CRVAL[1]
dec0<-astr$CRVAL[2]
x0<-astr$CRPIX[1]
y0<-astr$CRPIX[2]
xscale<-astr$CD[1,1]
yscale<-astr$CD[2,2]
#Determine the pixel-locations of the aperture catalogue objects
xy<-radec.to.xy(ra=ApCat.sample$RAdeg,dec=ApCat.sample$DECdeg, ra0=ra0,
dec0=dec0, x0=x0, y0=y0, xscale=xscale, yscale=yscale)
#Print sample
print(head(xy))

#Show the positions on the image
#Plot the Image
image(x=1:length(SDSS.sample$dat[[1]][,1]),
y=1:length(SDSS.sample$dat[[1]][1,]),
z=SDSS.sample$dat[[1]],col=grey.colors(1E3),
zlim=quantile(SDSS.sample$dat[[1]],c(0,0.995)),useRaster=TRUE,
xlab="X (pix)",ylab="Y (pix)",asp=1)
#Overlay the points
points(xy,pch=3,col='red')

AngusWright/LAMBDAR documentation built on May 12, 2022, 1:49 a.m.