heliographic_carrington coordinates

[Mat]

Hi,

I have a map in Helioprojective coordinates and I want to transform it in heliographic carrington with projection code "CEA". I obtaine the error:

"This transformation cannot be performed because the Heliographic Carrington frame has observer=None."

I attach you the code that i have used:

import matplotlib.pyplot as plt
from reproject import reproject_interp

import astropy.units as u
from astropy.coordinates import SkyCoord
from astropy.wcs import WCS
import sunpy.map


shape_out = [720, 1440]
frame_out = SkyCoord(0, 0, unit=u.deg,
                     frame="heliographic_carrington",
                     obstime=my_map.date)
header = sunpy.map.make_fitswcs_header(shape_out,
                                       frame_out,
                                       scale=[180 / shape_out[0],
                                              360 / shape_out[1]] * u.deg / u.pix,
                                       projection_code="CEA")

out_wcs = WCS(header)

array, footprint = reproject_interp(my_map, out_wcs, shape_out=shape_out)
outmap = sunpy.map.Map((array, header))

Thank you for the help

[Stuart Mumford]

(Quick reply from my phone)

Set the observer= keyword in your call to SkyCoord

Stuart

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Sent from my Android device with K-9 Mail. Please excuse my brevity.

[Mat]

Hi,

thank you for the answer.

I have tried this:

frame_out = SkyCoord(0, 0, unit=u.deg,
                     frame="

heliographic_carrington",
                     obstime=my_map.date, observer='earth')
but it still doesn't work


Mat

[Albert Y. Shih]

Hi, Mat,

     I think you've uncovered a bug: the WCS object created from the header isn't preserving the observer information as needed for `HeliographicCarrington`.  Until that bug is fixed, you can get your code to work by adding this line after `out_wcs` is created:

```

out_wcs.coordinate_frame = frame_out.frame

```

This line, which I emphasize shouldn't actually be necessary here, passes along an already created frame object so that one isn't constructed from the WCS information.

     Incidentally, you shouldn't specify `observer='earth'`, because that presumably is just an approximation to your actual observer location.  You imply that `my_map` is in `Helioprojective` coordinates, so there should be a defined observer that you can re-use for the `HeliographicCarrington` frame: `observer=my_map.observer_coordinate`.

Albert

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[Albert Y. Shih]

Hi, Mat,

     Sorry, I forgot that the WCS object currently doesn't understand the observer position for any coordinate frame, so it has to be manually set.  Rather than what I suggested in my previous email, you should add this line after creating `out_wcs`:

```

out_wcs.heliographic_observer = my_map.observer_coordinate

```

Albert