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Add URL support to DataAccessor #245

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Add URL support to DataAccessor #245

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Add URL support to DataAccessor (.vrt in a local folder if filename i…
whyjz Mar 3, 2021
53c492e
Update components/iscesys/ImageApi/DataAccessor/DataAccessorPy.py
whyjz Mar 4, 2021
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7 changes: 6 additions & 1 deletion components/iscesys/ImageApi/DataAccessor/DataAccessorPy.py
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Original file line number Diff line number Diff line change
Expand Up @@ -142,7 +142,12 @@ def createAccessor(self):
caster = '' or self.caster
filename = self.filename
scheme = self.scheme
self.extraFilename = self.filename + '.' + self._extra_reader
#if the filename is a URL, the extraFilename should indicate the file from the local machine
#instead of from the remote server.
if self.filename.startswith('http'):
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Suggested change
if self.filename.startswith('http'):
if self.filename.startswith('http://') or self.filename.startswith('https://'):

It may be possible someone's filename starts with http, but I wouldn't expect a local filename to contain //

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Why not create a .vrt and .xml and have source in vrt to point to remote? That way you have a record of what resource was actually used? That way you are not restricted to something thats just http / https. You can throw in anything vsis3 / vsiaz/ vsicurl etc. This approach still seems to need a .vrt. Just using basename of .vrt should be enough when it points to other things?

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@whyjz whyjz Mar 4, 2021 •
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@piyushrpt I did create a .vrt that points to a remote geotiff. In my use case, the XML is not needed. Here's an example of what would happen if running this snippet using the original code version:

import isce
from isceobj.Image.Image import Image
obj = Image()
obj.setFilename("https://download.osgeo.org/geotiff/samples/GeogToWGS84GeoKey/GeogToWGS84GeoKey5.tif")
obj.setWidth(101)
obj.setDataType('SHORT')
obj.setCaster('read', 'FLOAT')
obj.createImage()
# ... (continue to some Ampcor code)

GDAL open (R): https://download.osgeo.org/geotiff/samples/GeogToWGS84GeoKey/GeogToWGS84GeoKey5.tif.vrt
ERROR 1: HTTP error code : 404
Error. Cannot open the file https://download.osgeo.org/geotiff/samples/GeogToWGS84GeoKey/GeogToWGS84GeoKey5.tif.vrt in read mode.
Error in file /home/whyj/Software/isce2-2.4.2-build/isce/components/iscesys/ImageApi/InterleavedAccessor/src/GDALAccessor.cpp at line 77 Exiting

You can see that the ISCE's default behavior is to read a VRT that is at the same location as the original file, and it does not matter whether you have created a VRT on your local machine or not. If we replace the geotiff file name with the local vrt, ISCE will try to gdal open .vrt.vrt, which does not exist.

self.extraFilename = os.path.basename(self.filename) + '.' + self._extra_reader
else:
self.extraFilename = self.filename + '.' + self._extra_reader

if self._accessor is None:#to avoid creating duplicates
selection = self.methodSelector()
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