--- header unit 0: primary ---
SIMPLE = T / conforms to FITS standard
BITPIX = -64 / array data type
NAXIS = 3 / number of array dimensions
NAXIS1 = 51
NAXIS2 = 51
NAXIS3 = 6
EXTEND = T
X0 = 2101.463385435778 / x offset for shifting position
Y0 = 1974.284083767825 / y offset for shifting position
XSCALE = 4041.798854181518 / x scale for scaling object position
YSCALE = 4024.403515690077 / y scale for scaling object position
ORDER = 2 / polynomical order of PRF spatial variation
PIXSAMP = 0.5 / pixel scampling of the PRF
NSTARS = 334 / number of stars to calculate PRF
FWHM = 5.153556591784315 / FWHM of PSF at original pixel scale
COMMENT primary HDU data is the polynomical coffients for spatially variable PRF
COMMENT o=order,xs=xscale,ys=yscale,pixsamp, then PSF can be caculated as sum(i=
COMMENT 0:o,sum(j=0:o-i,((x-x0)/xs)^j*((y-y0)/ys)^i*data[k++]))+par*data[k++]+pa
COMMENT r*data[k++]^2+...