astLib.astWCS

57 """This class provides methods for accessing information from the World 58 Coordinate System (WCS) contained in the header of a FITS image. 59 Conversions between pixel and WCS coordinates can also be performed. 60 61 To create a WCS object from a FITS file called "test.fits", simply: 62 63 WCS=astWCS.WCS("test.fits") 64 65 Likewise, to create a WCS object from the pyfits.header of "test.fits": 66 67 img=pyfits.open("test.fits") 68 header=img[0].header 69 WCS=astWCS.WCS(header, mode = "pyfits") 70 71 """ 72

73 - def __init__(self, 74 headerSource, 75 extensionName=0, 76 mode="image", 77 zapKeywords=[]):

78 """Creates a WCS object using either the information contained in the 79 header of the specified .fits image, or from a pyfits.header object. 80 Set mode = "pyfits" if the headerSource is a pyfits.header. 81 82 For some images from some archives, particular header keywords such as 83 COMMENT or HISTORY may contain unprintable strings. If you encounter 84 this, try setting zapKeywords = ['COMMENT', 'HISTORY'] (for example). 85 86 @type headerSource: string or pyfits.header 87 @param headerSource: filename of input .fits image, or a pyfits.header 88 object 89 @type extensionName: int or string 90 @param extensionName: name or number of .fits extension in which image 91 data is stored 92 @type mode: string 93 @param mode: set to "image" if headerSource is a .fits file name, or 94 set to "pyfits" if headerSource is a pyfits.header object 95 @type zapKeywords: list 96 @param: zapKeywords: keywords to remove from the header before making 97 astWCS object. 98 99 @note: The meta data provided by headerSource is stored in WCS.header 100 as a pyfits.header object. 101 102 """ 103 104 self.mode = mode 105 self.headerSource = headerSource 106 self.extensionName = extensionName 107 108 if self.mode == "image": 109 img = pyfits.open(self.headerSource) 110 # silentfix below won't deal with unprintable strings 111 # so here we optionally remove problematic keywords 112 for z in zapKeywords: 113 if z in img[self.extensionName].header.keys(): 114 for count in range(img[self.extensionName].header.count( 115 z)): 116 img[self.extensionName].header.remove(z) 117 img.verify( 118 'silentfix') # solves problems with non-standard headers 119 self.header = img[self.extensionName].header 120 img.close() 121 elif self.mode == "pyfits": 122 for z in zapKeywords: 123 if z in self.headerSource.keys(): 124 for count in range(self.headerSource.count(z)): 125 self.headerSource.remove(z) 126 self.header = headerSource 127 128 self.updateFromHeader()

129

130 - def copy(self):

131 """Copies the WCS object to a new object. 132 133 @rtype: astWCS.WCS object 134 @return: WCS object 135 136 """ 137 138 # This only sets up a new WCS object, doesn't do a deep copy 139 ret = WCS(self.headerSource, self.extensionName, self.mode) 140 141 # This fixes copy bug 142 ret.header = self.header.copy() 143 ret.updateFromHeader() 144 145 return ret

146

147 - def updateFromHeader(self):

148 """Updates the WCS object using information from WCS.header. This 149 routine should be called whenever changes are made to WCS keywords in 150 WCS.header. 151 152 """ 153 154 # Updated for pyfits 3.1+ 155 newHead = pyfits.Header() 156 for i in self.header.items(): 157 if len(str(i[1])) < 70: 158 if len(str(i[0])) <= 8: 159 newHead.append((i[0], i[1])) 160 else: 161 newHead.append(('HIERARCH ' + i[0], i[1])) 162 163 # Workaround for ZPN bug when PV2_3 == 0 (as in, e.g., ESO WFI images) 164 if "PV2_3" in list(newHead.keys()) and newHead[ 165 'PV2_3'] == 0 and newHead['CTYPE1'] == 'RA---ZPN': 166 newHead["PV2_3"] = 1e-15 167 168 cardstring = "" 169 for card in newHead.cards: 170 cardstring = cardstring + str(card) 171 172 self.WCSStructure = wcs.wcsinit(cardstring)

173

174 - def getCentreWCSCoords(self):

175 """Returns the RA and dec coordinates (in decimal degrees) at the 176 centre of the WCS. 177 178 @rtype: list 179 @return: coordinates in decimal degrees in format [RADeg, decDeg] 180 181 """ 182 full = wcs.wcsfull(self.WCSStructure) 183 184 RADeg = full[0] 185 decDeg = full[1] 186 187 return [RADeg, decDeg]

188

189 - def getFullSizeSkyDeg(self):

190 """Returns the width, height of the image according to the WCS in 191 decimal degrees on the sky (i.e., with the projection taken into 192 account). 193 194 @rtype: list 195 @return: width and height of image in decimal degrees on the sky in 196 format [width, height] 197 198 """ 199 full = wcs.wcsfull(self.WCSStructure) 200 201 width = full[2] 202 height = full[3] 203 204 return [width, height]

205

206 - def getHalfSizeDeg(self):

207 """Returns the half-width, half-height of the image according to the 208 WCS in RA and dec degrees. 209 210 @rtype: list 211 @return: half-width and half-height of image in R.A., dec. decimal 212 degrees in format [half-width, half-height] 213 214 """ 215 half = wcs.wcssize(self.WCSStructure) 216 217 width = half[2] 218 height = half[3] 219 220 return [width, height]

221

222 - def getImageMinMaxWCSCoords(self):

223 """Returns the minimum, maximum WCS coords defined by the size of the 224 parent image (as defined by the NAXIS keywords in the image header). 225 226 @rtype: list 227 @return: [minimum R.A., maximum R.A., minimum Dec., maximum Dec.] 228 229 """ 230 231 # Get size of parent image this WCS is taken from 232 maxX = self.header['NAXIS1'] 233 maxY = self.header['NAXIS2'] 234 minX = 1.0 235 minY = 1.0 236 237 if NUMPY_MODE: 238 maxX = maxX - 1 239 maxY = maxY - 1 240 minX = minX - 1 241 minY = minY - 1 242 243 bottomLeft = self.pix2wcs(minX, minY) 244 topRight = self.pix2wcs(maxX, maxY) 245 246 xCoords = [bottomLeft[0], topRight[0]] 247 yCoords = [bottomLeft[1], topRight[1]] 248 xCoords.sort() 249 yCoords.sort() 250 251 return [xCoords[0], xCoords[1], yCoords[0], yCoords[1]]

252

253 - def wcs2pix(self, RADeg, decDeg):

254 """Returns the pixel coordinates corresponding to the input WCS 255 coordinates (given in decimal degrees). RADeg, decDeg can be single 256 floats, or lists or numpy arrays. 257 258 @rtype: list 259 @return: pixel coordinates in format [x, y] 260 261 """ 262 263 if type(RADeg) == numpy.ndarray or type(RADeg) == list: 264 if type(decDeg) == numpy.ndarray or type(decDeg) == list: 265 pixCoords = [] 266 for ra, dec in zip(RADeg, decDeg): 267 pix = wcs.wcs2pix(self.WCSStructure, float(ra), float(dec)) 268 # Below handles CEA wraparounds 269 if pix[0] < 1: 270 xTest = ((self.header['CRPIX1']) - 271 (ra - 360.0) / self.getXPixelSizeDeg()) 272 if xTest >= 1 and xTest < self.header['NAXIS1']: 273 pix[0] = xTest 274 if NUMPY_MODE: 275 pix[0] = pix[0] - 1 276 pix[1] = pix[1] - 1 277 pixCoords.append([pix[0], pix[1]]) 278 else: 279 pixCoords = (wcs.wcs2pix(self.WCSStructure, float(RADeg), 280 float(decDeg))) 281 # Below handles CEA wraparounds 282 if pixCoords[0] < 1: 283 xTest = ((self.header['CRPIX1']) - 284 (RADeg - 360.0) / self.getXPixelSizeDeg()) 285 if xTest >= 1 and xTest < self.header['NAXIS1']: 286 pixCoords[0] = xTest 287 if NUMPY_MODE: 288 pixCoords[0] = pixCoords[0] - 1 289 pixCoords[1] = pixCoords[1] - 1 290 pixCoords = [pixCoords[0], pixCoords[1]] 291 292 return pixCoords

293

294 - def pix2wcs(self, x, y):

295 """Returns the WCS coordinates corresponding to the input pixel 296 coordinates. 297 298 @rtype: list 299 @return: WCS coordinates in format [RADeg, decDeg] 300 301 """ 302 if type(x) == numpy.ndarray or type(x) == list: 303 if type(y) == numpy.ndarray or type(y) == list: 304 WCSCoords = [] 305 for xc, yc in zip(x, y): 306 if NUMPY_MODE: 307 xc += 1 308 yc += 1 309 WCSCoords.append(wcs.pix2wcs(self.WCSStructure, float(xc), 310 float(yc))) 311 else: 312 if NUMPY_MODE: 313 x += 1 314 y += 1 315 WCSCoords = wcs.pix2wcs(self.WCSStructure, float(x), float(y)) 316 317 return WCSCoords

318

319 - def coordsAreInImage(self, RADeg, decDeg):

320 """Returns True if the given RA, dec coordinate is within the image 321 boundaries. 322 323 @rtype: bool 324 @return: True if coordinate within image, False if not. 325 326 """ 327 328 pixCoords = wcs.wcs2pix(self.WCSStructure, RADeg, decDeg) 329 if pixCoords[0] >= 0 and pixCoords[0] < self.header['NAXIS1'] and \ 330 pixCoords[1] >= 0 and pixCoords[1] < self.header['NAXIS2']: 331 return True 332 else: 333 return False

334

335 - def getRotationDeg(self):

336 """Returns the rotation angle in degrees around the axis, North through 337 East. 338 339 @rtype: float 340 @return: rotation angle in degrees 341 342 """ 343 return self.WCSStructure.rot

344

345 - def isFlipped(self):

346 """Returns 1 if image is reflected around axis, otherwise returns 0. 347 348 @rtype: int 349 @return: 1 if image is flipped, 0 otherwise 350 351 """ 352 return self.WCSStructure.imflip

353

354 - def getPixelSizeDeg(self):

355 """Returns the pixel scale of the WCS. This is the average of the x, y 356 pixel scales. 357 358 @rtype: float 359 @return: pixel size in decimal degrees 360 361 """ 362 363 avSize = ( 364 abs(self.WCSStructure.xinc) + abs(self.WCSStructure.yinc)) / 2.0 365 366 return avSize

367

368 - def getXPixelSizeDeg(self):

369 """Returns the pixel scale along the x-axis of the WCS in degrees. 370 371 @rtype: float 372 @return: pixel size in decimal degrees 373 374 """ 375 376 avSize = abs(self.WCSStructure.xinc) 377 378 return avSize

379

380 - def getYPixelSizeDeg(self):

381 """Returns the pixel scale along the y-axis of the WCS in degrees. 382 383 @rtype: float 384 @return: pixel size in decimal degrees 385 386 """ 387 388 avSize = abs(self.WCSStructure.yinc) 389 390 return avSize

391

392 - def getEquinox(self):

393 """Returns the equinox of the WCS. 394 395 @rtype: float 396 @return: equinox of the WCS 397 398 """ 399 return self.WCSStructure.equinox

400

401 - def getEpoch(self):

402 """Returns the epoch of the WCS. 403 404 @rtype: float 405 @return: epoch of the WCS 406 407 """ 408 return self.WCSStructure.epoch

Source Code for Module astLib.astWCS