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Coordinate system and footprint

Coordinate system and footprint#

4 coordinate systems#

There are 4 coordinates system in ztfimg: - xy: pixel position of the image (“quadrant” pixels) - ij: ccd pixel coordinates (xy and ij are the equal for CCD image) - uv: focal plane coordinates (in arcsec) - radec: sky coordinates

In all cases, systems coordinates are: +Dec (North) upward and +RA (East) rightward.

system conversion tools#

ztfimg.ScienceQuadrant, that have a wcs solution, hold the conversion system method such as xy_to_radec() or uv_to_ij() ; all combination exists.

[2]:

import ztfimg
qimg = ztfimg.ScienceQuadrant.from_filename("ztf_20200924431759_000655_zr_c13_o_q2_sciimg.fits",
                                   as_path=False)

ij | ccd coordinates#

remember that ccds are as such:

q2 | q1
--------
q3 | q4

So q1 and q2 y-values have +“quadrant-y-shape” for y and q1 and q4 have +“quadrant-x-shape” for their x

[3]:

print(qimg.qid)
qimg.xy_to_ij(10,10)

2

[3]:

array([  10, 3090])

uv | focal plane coordinates#

The uv coordinates contains the tangent plane coordinates to know the location of the element within the full focal plane.

So, for instance, the 0,0 pixel is approximatly at position ~7000, 10_000 arcsec within the focalplane

[24]:

qimg.xy_to_uv(0,0).squeeze()

[24]:

array([ 7031.58753668, 10320.50186255])

radec | sky coordinates#

finally the (40, 300), and (1700,801) xy-pixels corresponds (for this exposure)

[25]:

ra,dec = qimg.xy_to_radec([40, 1700],[300, 801])
ra,dec

[25]:

(array([57.4935367 , 58.07736917]), array([36.2742405 , 36.40336741]))

system conversion tools#

When requesting image center or corners, the system method option enable you to choose which system you want the results in.

  • get_center(): center of the image (quadrant or ccd)

  • get_corners(): corners of the image (quadrant or ccd) | lower-left, lower-right, upper-right, upper-left

[26]:

qimg.get_center(system="ij")

[26]:

array([1536.5, 4620.5])

[27]:

qimg.get_corners("uv")

[27]:

array([[ 7031.58753668, 10320.50186255],
       [10151.5276707 , 10329.57701145],
       [10150.9176875 , 13462.39473092],
       [ 7029.41028383, 13450.96916209]])

show footprint (FocalPlane and CCD)#

The show_footprint() method enables you to display the quadrants or ccd colored by a single value (or None).

[28]:

ccd = qimg.get_ccd()

[29]:

fp = qimg.get_focalplane()

[30]:

_ = ccd.show_footprint()

[31]:

_ = fp.show_footprint()

put any attribute, or result or quadrant.get_value() like the header key MAGZP

[32]:

_ = fp.show_footprint("MAGZP")
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