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I have 3 raster files (.tiff files) which are geographically 3 consecutive tiles of a particular area. I am trying to make a .vrt file of 2 out of these 3 files using the gdalbuildvrt python command. The issue I am facing is suppose if I am making a .vrt file (named test.vrt) of the first 2 files (say file 1 & 2) and opening it with rasterio python, it's opening correctly. Subsequently, I want to create a .vrt file of the new file combinations (say file 1 & 3) and overwrite the old .vrt file (test.vrt) with this file combination and try to open it with rasterio python. The problem I am facing now is it's still displaying the the .vrt file with the old file combinations (having files 1 & 2 and not files 1 & 3). The code which I used till now is:

import rasterio 
import rasterio.plot

from osgeo import gdal

vrt_options = gdal.BuildVRTOptions(resampleAlg='cubic', addAlpha=True)
test_vrt = gdal.BuildVRT(r'D:\Test TIFF\test.vrt', [r'D:\Test TIFF\Tile_58_LULC250k_2015_16_revised.tif', r'D:\Test TIFF\Tile_60_LULC250k_2015_16_revised.tif'], options=vrt_options)

test_vrt = None

raster_vrt = rasterio.open(r'D:\Test TIFF\test.vrt')

rasterio.plot.show(raster_vrt)

Also, if I am opening this new .vrt file with QGIS its displaying the correct file combinations (file 1 & 3). So what I understood is the .vrt file has changed after running the gdalbuildvrt command but there is some problem while opening it with rasterio python because it's displaying old .vrt file (file 1 & 2).

Can someone help me figure out what is the problem?

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  • Could be a race condition, or some kind of file cache. To confirm, try give each combination of files a different VRT file name, rather than re-using "D:\Test TIFF\test.vrt". If that's the case, then work on a different strategy for creating your VRTs, one that emphasises atomicity. e.g. write to a temporary file, then move (mv in Linux) the temporary file once it has been written and closed. See for example: stackoverflow.com/questions/2333872/… This is to avoid prematurely reading a file that hasn't actually been (over-)written.
    – alphabetasoup
    May 10, 2019 at 4:29
  • Thanks @RichardLaw for your kind suggestion. I just added raster_vrt.close() at the end of the program and the issue got resolved. Now I am able to overwrite the same vrt file with different file combinations.
    – RRSC NGP
    May 10, 2019 at 4:55

2 Answers 2

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2

A common idiom is to use a with statement when opening a file so that it is automatically closed when the with block is complete. To adapt the existing answer:

import rasterio 
import rasterio.plot

from osgeo import gdal

vrt_options = gdal.BuildVRTOptions(resampleAlg='cubic', addAlpha=True)
test_vrt = gdal.BuildVRT(r'D:\Test TIFF\test.vrt', [r'D:\Test TIFF\Tile_58_LULC250k_2015_16_revised.tif', r'D:\Test TIFF\Tile_60_LULC250k_2015_16_revised.tif'], options=vrt_options)

test_vrt = None

with rasterio.open(r'D:\Test TIFF\test.vrt') as raster_vrt:

    rasterio.plot.show(raster_vrt)
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1

With kind suggestion from @Richard Law, adding raster_vrt.close() at the end of the program solved the issue....

import rasterio 
import rasterio.plot

from osgeo import gdal

vrt_options = gdal.BuildVRTOptions(resampleAlg='cubic', addAlpha=True)
test_vrt = gdal.BuildVRT(r'D:\Test TIFF\test.vrt', [r'D:\Test TIFF\Tile_58_LULC250k_2015_16_revised.tif', r'D:\Test TIFF\Tile_60_LULC250k_2015_16_revised.tif'], options=vrt_options)

test_vrt = None

raster_vrt = rasterio.open(r'D:\Test TIFF\test.vrt')

rasterio.plot.show(raster_vrt)

raster_vrt.close()
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  • 5
    You could also do with rasterio.open('D:\Test TIFF\test.vrt') as vrt: which would implicitly close the file when appropriate. This is a very common pattern in Python. effbot.org/zone/python-with-statement.htm
    – alphabetasoup
    May 10, 2019 at 5:14
  • 1
    Yup definitely that will be an another option as well.... :) Thanks @RichardLaw
    – RRSC NGP
    May 10, 2019 at 6:25
  • @alphabetasoup please turn that into an answer so that we can vote it higher than this one ;)
    – bugmenot123
    Mar 3, 2020 at 14:19
  • 1
    @bugmenot123 done
    – alphabetasoup
    Mar 3, 2020 at 19:39

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