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Display from one plane to another plane despite masking areas

I have a dataset shown here where the first and second columns are the coordinates of the sky (ra, dec), respectively, and the third and fourth are the coordinates in the Cartesian system (x, y).

enter image description here

I need to render a 2D interpolation surface using the coordinates x

and y

and the other using the Ra

and Dec

. The problem is the existence of masked areas as shown in the picture above. I can illustrate the missing data by simply plotting it (there is a value in the directory NaN

). This is what I have tried so far and did not give the correct answer:

from scipy.interpolate import griddata
import numpy as np
import matplotlib.pyplot as plt

data = np.loadtxt('test.asc')

ra = data[:,0]
dec = data[:,1]
Xpos = data[:,2]
Ypos = data[:,3]

xi = np.linspace(Xpos.min(), Xpos.max(), 1000)
yi = np.linspace(Ypos.min(), Ypos.max(), 1000)
xi, yi = np.meshgrid(xi, yi, copy=False)
ra_int = griddata(data[:,2:4], ra, (xi.flatten(), yi.flatten()),
                  method='cubic')
dec_int = griddata(data[:,2:4], dec, (xi.flatten(), yi.flatten()),
                   method='cubic')

Usage griddata

fails and only returns values NaN

. Is there a way to do this interpolation to estimate values ​​to Ra

and Dec

from given coordinates x

and y

even masked areas (map from x

and y

to Ra

and Dec

)?

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1 answer


If I understood correctly, it looks like this:

CCD projection

just shift the Cartesian coordinate system to the middle of the CCD , and also the equatorial coordinates to the middle of the CCD . Then calculate x,y

separately. The only thing you need is to calculate the focus length f

separately for x

and y

!!!


pos

is a Cartesian coordinate (x or y)
ang

is an equatorial coordinate (RA or Dec)



  • get edge point from database

    slide the corners to the middle of the CCD

  • calculate focus (fx,fy)

    from it

    f = pos/tan(ang)

  • now you can compute the projection for any record in the dataset

    shift the corners to the middle of the CCD , then calculate x,y

    by

    pos=f*tan(ang)

    slide back from the CCD from the middle to the original Cartesian coordinates. You have to check several points if this approach is correct

[notes]

x

the axis is reflected in your output, so just use x=-x

at the end before moving to the original cartesian coordinates or leaving the focus f

negative.

if your CCD is not axially oriented to the equator, you need to calculate the rotation (the angle between the axis x

and the equator) and apply the rotation around the axis Z

after transformation before shifting back ...

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