Added warning when json file cannot be written out

        if model_name is None:

            return

        isdpath = os.path.splitext(self['image_path'])[0] + '.json'

        try:

            with open(isdpath, 'w') as f:

                json.dump(response, f)

        except:

            warnings.warn('Failed to write JSON ISD for image {}'.format(self['image_path']))

        isd = csmapi.Isd(self['image_path'])

        plugin = csmapi.Plugin.findPlugin('UsgsAstroPluginCSM')

        self._camera = plugin.constructModelFromISD(isd, model_name)