python - 为什么 WCS 投影子图上的特征在 matplotlib 中位于错误的位置？

Question

我有一个关于天文物体的拟合文件。我可以这样绘制:

from astropy.io import fits
from astropy.wcs import WCS

hdul = fits.open(fitsfilename)[0]

wcs = WCS(hdul.header)
fig = plt.figure(figsize=(12,12))
fig.add_subplot(111, projection=wcs)
plt.imshow(hdul.data)

这有效，并产生了漂亮的图片:

我想向该图中添加一些附加功能，但这不起作用。例如，让我们尝试将一个圆添加到 119°, -67°30'。我通过以下方式扩展代码:

plt.scatter([119],[-67.5],c='r',s=500)

我得到的是:

这确实不是我们想要的，圆在 118°5', -67°5' 附近，而不是它应该在的位置 (119°, -67°30')。

我做错了什么，或者这个问题有什么好的解决办法？

<小时/>

注意:当我运行 wcs = WCS(hdul.header) 时，我收到警告:

WARNING: VerifyWarning: Verification reported errors: [astropy.io.fits.verify] WARNING: VerifyWarning: Card 'A_2_0' is not FITS standard (invalid value string: '3.29341755408e-05'). Fixed 'A_2_0' card to meet the FITS standard. [astropy.io.fits.verify] WARNING: VerifyWarning: Note: astropy.io.fits uses zero-based indexing. [astropy.io.fits.verify] WARNING: VerifyWarning: Card 'A_1_1' is not FITS standard (invalid value string: '1.51709339878e-05'). Fixed 'A_1_1' card to meet the FITS standard. [astropy.io.fits.verify] WARNING: VerifyWarning: Card 'A_0_2' is not FITS standard (invalid value string: '5.17973753556e-06'). Fixed 'A_0_2' card to meet the FITS standard. [astropy.io.fits.verify] WARNING: VerifyWarning: Card 'B_2_0' is not FITS standard (invalid value string: '2.97627426087e-06'). Fixed 'B_2_0' card to meet the FITS standard. [astropy.io.fits.verify] WARNING: VerifyWarning: Card 'B_1_1' is not FITS standard (invalid value string: '2.71948126373e-05'). Fixed 'B_1_1' card to meet the FITS standard. [astropy.io.fits.verify] WARNING: VerifyWarning: Card 'B_0_2' is not FITS standard (invalid value string: '1.66848449653e-05'). Fixed 'B_0_2' card to meet the FITS standard. [astropy.io.fits.verify] WARNING: VerifyWarning: Card 'AP_1_0' is not FITS standard (invalid value string: '1.79541533196e-06'). Fixed 'AP_1_0' card to meet the FITS standard. [astropy.io.fits.verify] WARNING: VerifyWarning: Card 'AP_0_1' is not FITS standard (invalid value string: '9.20624843151e-07'). Fixed 'AP_0_1' card to meet the FITS standard. [astropy.io.fits.verify] WARNING: VerifyWarning: Card 'AP_2_0' is not FITS standard (invalid value string: '-3.29292923201e-05'). Fixed 'AP_2_0' card to meet the FITS standard. [astropy.io.fits.verify] WARNING: VerifyWarning: Card 'AP_1_1' is not FITS standard (invalid value string: '-1.51738446887e-05'). Fixed 'AP_1_1' card to meet the FITS standard. [astropy.io.fits.verify] WARNING: VerifyWarning: Card 'AP_0_2' is not FITS standard (invalid value string: '-5.18321445978e-06'). Fixed 'AP_0_2' card to meet the FITS standard. [astropy.io.fits.verify] WARNING: VerifyWarning: Card 'BP_1_0' is not FITS standard (invalid value string: '8.99029048217e-07'). Fixed 'BP_1_0' card to meet the FITS standard. [astropy.io.fits.verify] WARNING: VerifyWarning: Card 'BP_0_1' is not FITS standard (invalid value string: '1.15967736014e-06'). Fixed 'BP_0_1' card to meet the FITS standard. [astropy.io.fits.verify] WARNING: VerifyWarning: Card 'BP_2_0' is not FITS standard (invalid value string: '-2.97837492348e-06'). Fixed 'BP_2_0' card to meet the FITS standard. [astropy.io.fits.verify] WARNING: VerifyWarning: Card 'BP_1_1' is not FITS standard (invalid value string: '-2.71998518336e-05'). Fixed 'BP_1_1' card to meet the FITS standard. [astropy.io.fits.verify] WARNING: VerifyWarning: Card 'BP_0_2' is not FITS standard (invalid value string: '-1.66872388359e-05'). Fixed 'BP_0_2' card to meet the FITS standard. [astropy.io.fits.verify] WARNING: VerifyWarning: Card 'WCSR_PRJ' is not FITS standard (invalid value string: '3.6679e-07'). Fixed 'WCSR_PRJ' card to meet the FITS standard. [astropy.io.fits.verify] WARNING: VerifyWarning: Card 'WCSR_PIX' is not FITS standard (invalid value string: '8.2565e-05'). Fixed 'WCSR_PIX' card to meet the FITS standard. [astropy.io.fits.verify]

所以这可能是相关的；如何修复它的问题仍然存在。

Answer 1

在 world coordinates 中绘制，您需要指定转换，例如:

ax = fig.gca()
ax.scatter([34], [3.2], transform=ax.get_transform('world'))

通常，您可以忽略这些 FITS header 警告，因为没有任何 FITS header 卡与 WCS 相关(据我所知)。