def prepare_mosaic(self, image, fov_deg, name=None):
        """Prepare a new (blank) mosaic image based on the pointing of
        the parameter image
        """
        header = image.get_header()
        ra_deg, dec_deg = header['CRVAL1'], header['CRVAL2']

        data_np = image.get_data()
        #dtype = data_np.dtype
        dtype = None
        self.bg_ref = iqcalc.get_median(data_np)

        # TODO: handle skew (differing rotation for each axis)?

        skew_limit = self.settings.get('skew_limit', 0.1)
        (rot_deg, cdelt1, cdelt2) = wcs.get_rotation_and_scale(header,
                                                               skew_threshold=skew_limit)
        self.logger.debug("image0 rot=%f cdelt1=%f cdelt2=%f" % (
            rot_deg, cdelt1, cdelt2))

        # TODO: handle differing pixel scale for each axis?
        px_scale = math.fabs(cdelt1)
        cdbase = [numpy.sign(cdelt1), numpy.sign(cdelt2)]

        reuse_image = self.settings.get('reuse_image', False)
        if (not reuse_image) or (self.img_mosaic not in None):
            self.logger.debug("creating blank image to hold mosaic")
            self.fv.gui_do(self._prepare_mosaic1, "Creating blank image...")

            # GC old mosaic
            self.img_mosaic = None

            img_mosaic = dp.create_blank_image(ra_deg, dec_deg,
                                               fov_deg, px_scale,
                                               rot_deg,
                                               cdbase=cdbase,
                                               logger=self.logger,
                                               pfx='mosaic',
                                               dtype=dtype)

            if name is not None:
                img_mosaic.set(name=name)
            imname = img_mosaic.get('name', image.get('name', "NoName"))

            # avoid making a thumbnail of this if seed image is also that way
            nothumb = not self.settings.get('make_thumbs', False)
            if nothumb:
                img_mosaic.set(nothumb=True)
            else:
                # image is not on disk, set indication for other plugins
                img_mosaic.set(path=None)

            # TODO: fill in interesting/select object headers from seed image

            self.img_mosaic = img_mosaic
            self.fv.gui_call(self.fv.add_image, imname, img_mosaic,
                             chname=self.mosaic_chname)

        else:
            # <-- reuse image (faster)
            self.logger.debug("Reusing previous mosaic image")
            self.fv.gui_do(self._prepare_mosaic1, "Reusing previous mosaic image...")

            img_mosaic = dp.recycle_image(self.img_mosaic,
                                          ra_deg, dec_deg,
                                          fov_deg, px_scale,
                                          rot_deg,
                                          cdbase=cdbase,
                                          logger=self.logger,
                                          pfx='mosaic')

        header = img_mosaic.get_header()
        (rot, cdelt1, cdelt2) = wcs.get_rotation_and_scale(header,
                                                           skew_threshold=skew_limit)
        self.logger.debug("mosaic rot=%f cdelt1=%f cdelt2=%f" % (
            rot, cdelt1, cdelt2))

        return img_mosaic
dataset/ETHPy150Open ejeschke/ginga/ginga/misc/plugins/Mosaic.py/Mosaic.prepare_mosaic/operator `is` -> `not in`