getpixscale {celestial} | R Documentation |
Get Pixel Scale
Description
Given a FITSio
of astro
header, calculate the image pixel scale.
Usage
getpixscale(header, CD1_1 = 1, CD1_2 = 0, CD2_1 = 0, CD2_2 = 1)
Arguments
header |
Full FITS header in table or vector format. Legal table format headers are provided by the |
CD1_1 |
FITS header CD1_1 for the Tan Gnomonic projection system. Change in RA-Tan in degrees along x-Axis. |
CD1_2 |
FITS header CD1_2 for the Tan Gnomonic projection system. Change in RA-Tan in degrees along y-Axis. |
CD2_1 |
FITS header CD2_1 for the Tan Gnomonic projection system. Change in Dec-Tan in degrees along x-Axis. |
CD2_2 |
FITS header CD2_2 for the Tan Gnomonic projection system. Change in Dec-Tan in degrees along y-Axis. |
Details
In most cases users will simply provide a valid header to find the WCS, but you can enter the CD values explicitly. Calculating the pixel scale from the latter is almost trivial, but the option is there for the curious/lazy.
Value
Numeric scalar; the image pixscale in asec/pixel (so typically a value of 0.1-0.5 for modern survey instruments).
Author(s)
Aaron Robotham
Examples
## Not run:
#The answer should be almost exactly 0.2 asec/pixel:
#Using FITSio and ProFit packages
image = readFITS(system.file("extdata", 'KiDS/G266035fitim.fits', package="ProFit"))
getpixscale(image$hdr)
#Using astro package
image = read.fits(system.file("extdata", 'KiDS/G266035fitim.fits', package="ProFit"))
getpixscale(image$hdr[[1]])
## End(Not run)