R: Get Pixel Scale

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 `read.fitshdr` function or the hdr list output of `read.fits` in the astro package; the hdr output of `readFITS` in the `FITSio` package or the header output of `magcutoutWCS`. Missing header keywords are printed out and other header option arguments are used in these cases. See `xy2radec`.
`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"))
    profitGetPixScale(image$hdr)
    #Using astro package
    image = read.fits(system.file("extdata", 'KiDS/G266035fitim.fits', package="ProFit"))
    profitGetPixScale(image$hdr[[1]])

    ## End(Not run)

[Package celestial version 1.4.1 Index]