GDAL blocksize

gdal_blocksize.ipynb

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   "source": [
    "import gdal\n",
    "from tqdm import tqdm_notebook as tqdm"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {
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   "outputs": [],
   "source": [
    "# NOAA GFS gribfile\n",
    "ingrb = r'D:\\Data\\GFS_grib\\gfs.t00z.pgrb2.0p25.f015'"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {},
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   "source": [
    "ds = gdal.Open(ingrb)\n",
    "b1 = ds.GetRasterBand(1)"
   ]
  },
  {
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   "execution_count": 4,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "(1440, 721)"
      ]
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     "execution_count": 4,
     "metadata": {},
     "output_type": "execute_result"
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   ],
   "source": [
    "# Raster dimensions\n",
    "xs, ys = b1.XSize, b1.YSize\n",
    "xs, ys"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {},
   "outputs": [
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     "data": {
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     "execution_count": 5,
     "metadata": {},
     "output_type": "execute_result"
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   ],
   "source": [
    "# Blocksize of the file\n",
    "xbs, ybs = b1.GetBlockSize() # striped file layout, \"row-wise\"\n",
    "xbs, ybs"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {
    "collapsed": true
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   "outputs": [],
   "source": [
    "gdal.SetCacheMax(0) # Dont cache in order to force disk I/O (not a realistic scenario)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {},
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     "text": [
      "1 loop, best of 3: 1.39 s per loop\n"
     ]
    }
   ],
   "source": [
    "%%timeit\n",
    "# read column by column\n",
    "for colnum in range(xs):    \n",
    "    data = b1.ReadAsArray(xoff=colnum, yoff=0, win_xsize=1, win_ysize=ys)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "100 loops, best of 3: 10.8 ms per loop\n"
     ]
    }
   ],
   "source": [
    "%%timeit\n",
    "# read row by row\n",
    "for rownum in range(ys):    \n",
    "    data = b1.ReadAsArray(xoff=0, yoff=rownum, win_xsize=xs, win_ysize=1)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "ds = None # close the file"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
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    "collapsed": true
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   "outputs": [],
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