生成的FITS文件WCS不生效，SAO DS9仅显示像素坐标求助

我生成了包含随机恒星的FITS文件，文件头已添加WCS信息，但在SAO DS9中打开时，鼠标悬停只显示x、y像素坐标，看不到对应的天球坐标。以下是生成文件的Python脚本和DS9中的显示现象：

import numpy as np
from pathlib import Path
import matplotlib.pyplot as plt
import pandas as pd
import os
from astropy.wcs import WCS
from astropy import units as u
from astropy.io import fits
from astropy.visualization import AsinhStretch, LogStretch
from astropy.visualization.mpl_normalize import ImageNormalize
from convenience_functions import show_image
from photutils.datasets import make_gaussian_sources_image, make_random_gaussians_table
from astropy.nddata import Cutout2D

def add_wcs(cntrpix,cntrval,cdelt,ctype, radesys):
    #zhdrbb.remove('ZODIL')
    #CREATE WCS KEYWORDS
    w = WCS(naxis=2)
    w.wcs.crpix = cntrpix
    w.wcs.crval = cntrval
    w.wcs.cdelt = cdelt
    w.wcs.ctype = ctype
    w.wcs.radesys = radesys
    w.wcs.equinox = 2000
    w.wcs.set_pv([(2, 1, 45.0)])
    w.wcs.cunit = [u.deg, u.deg]

    header = w.to_header()
    return header

def stars(image, number, mag_min, mag_max):
    """
    Add some stars to the image.
    """

    # Most of the code below is a direct copy/paste from
    # https://photutils.readthedocs.io/en/stable/_modules/photutils/datasets/make.html#make_100gaussians_image

    flux_min = 10**mag_min
    flux_max = 10**mag_max
    flux_range = [flux_min, flux_max]

    y_max, x_max = image.shape
    xmean_range = [0.01 * x_max, 0.99 * x_max]
    ymean_range = [0.01 * y_max, 0.99 * y_max]
    xstddev_range = [4, 4]
    ystddev_range = [4, 4]
    params = dict([('flux', flux_range),
                  ('x_mean', xmean_range),
                  ('y_mean', ymean_range),
                  ('x_stddev', xstddev_range),
                  ('y_stddev', ystddev_range),
                  ('theta', [0, 2*np.pi])])
    
    sources = make_random_gaussians_table(number, params, seed=int(random.random()*1e4))

    star_im = make_gaussian_sources_image(image.shape, sources)

    return sources, star_im

RA_0, RA_F = 30, 70
DEC_0, DEC_F = -20,20
MAG_0, MAG_F = 3, 8
N_STARS = 250

D_RA = np.abs(RA_0 - RA_F)
D_DEC = np.abs(DEC_0 - DEC_F)

GRID_LENGTH = int(2e3) # N PIXELS PER SIDE

# WCS STUFF
CRPIX = (int(GRID_LENGTH / 2), int(GRID_LENGTH / 2))
CRVAL = (RA_0 + D_RA / 2., DEC_0 + D_DEC / 2.)

cdelt_x = D_RA / GRID_LENGTH
cdelt_y = D_DEC / GRID_LENGTH
CDELT = (cdelt_x, cdelt_y)
CTYPE = ["RA-TAN", "DEC-TAN"]
RADESYS = 'ICRS'
base_pix_full_image = np.zeros((GRID_LENGTH,GRID_LENGTH))
star_data, star_cat_img = stars(base_pix_full_image, N_STARS, MAG_0, MAG_F)
# WCS
wcs_header = add_wcs(CRPIX, CRVAL, CDELT, CTYPE, RADESYS)

hdr = fits.Header()
hdu_cat = fits.PrimaryHDU(header=wcs_header,data=star_cat_img)

# WRITE FITS PIXEL FILE
hdu_cat.writeto(fits_pixel_file, overwrite=True)

截图显示DS9窗口底部状态栏仅展示x: xxx y: xxx的像素坐标，无RA/DEC等天球坐标信息。

排查建议 #

• 检查WCS关键字完整性
  用fits.getheader(fits_pixel_file)导出文件头，确认核心WCS关键字存在且格式正确：

  • CRPIX1/CRPIX2：需匹配图像中心像素值
  • CRVAL1/CRVAL2：对应设置的天球中心坐标
  • CDELT1/CDELT2：每像素对应的角度值（单位应为度）
  • CTYPE1/CTYPE2：必须为RA-TAN和DEC-TAN
    注意：Astropy生成的CUNIT1/CUNIT2关键字若设置非度单位，可能导致DS9解析失败，可尝试删除该关键字后重新保存文件。

• 移除不必要的PV扭曲参数
  代码中w.wcs.set_pv([(2, 1, 45.0)])添加了DEC轴的扭曲项，对于无畸变的模拟图像，该参数可能干扰DS9的WCS解析。注释掉这一行，重新生成文件测试。

• 调整DS9坐标显示设置
  在DS9菜单栏选择Frame -> Coordinate System，确认已切换至ICRS（与代码中RADESYS='ICRS'匹配），而非Image模式。也可通过快捷键Ctrl+W快速切换坐标显示类型。

• 修复代码依赖问题
  stars函数中使用了random.random()但未导入random模块，运行时会抛出异常，导致生成的FITS文件可能不完整。需在代码开头添加import random。

• 验证WCS有效性
  用Astropy自带工具验证WCS转换是否正常：

  from astropy.io import fits
  from astropy.wcs import WCS
  
  hdul = fits.open(fits_pixel_file)
  wcs = WCS(hdul[0].header)
  print(wcs)
  # 测试中心像素转天球坐标
  pix_center = (GRID_LENGTH/2, GRID_LENGTH/2)
  sky_center = wcs.pixel_to_world(*pix_center)
  print(f"中心像素对应天球坐标：{sky_center}")
  

  若转换结果正确，说明WCS本身无问题，需重点检查DS9的设置。

内容的提问来源于stack exchange，提问作者anakha272