![]() Seeking to the end of the file, or at random locations, is similarly slow. ![]() VSIStatL() will return the uncompressed file size, but this is potentially a slow operation on large files, since it requires uncompressing the whole file. To view a gzipped file as uncompressed by GDAL, you must use the /vsigzip/path/to/the/file.gz syntax, where path/to/the/file.gz is relative or absolute. vsigzip/ is a file handler that allows on-the-fly reading of GZip (.gz) files without decompressing them in advance. The new zip must be closed before being re-opened in read mode. Read and write operations cannot be interleaved. This slightly reduces the compression rate, so very small chunk sizes should be avoided. By default the input stream is split into 1 MB chunks (the chunk size can be tuned with the CPL_VSIL_DEFLATE_CHUNK_SIZE configuration option, with values like “x K” or “x M”), and each chunk is independently compressed (and terminated by a nine byte marker 0x00 0x00 0xFF 0xFF 0x00 0x00 0x00 0xFF 0xFF, signaling a full flush of the stream and dictionary, enabling potential independent decoding of each chunk). This is similar to the pigz utility in independent mode. Starting with GDAL 2.4, the GDAL_NUM_THREADS configuration option can be set to an integer or ALL_CPUS to enable multi-threaded compression of a single file. Newfile = VSIFOpenL ( "/vsizip/my.zip/newfile", "wb" ) VSIFWriteL ( "Hello World", 1, strlen ( "Hello world" ), newfile ) VSIFCloseL ( newfile ) zip file contains a single file located at its root, just mentioning /vsizip/path/to/the/file.zip will work. Getting directory listing and file statistics are fast operations. Directories inside the ZIP file can be distinguished from regular files with the VSI_ISDIR(stat.st_mode) macro as for regular file systems. A VSIStatL() (“/vsizip/…”) call will return the uncompressed size of the file. ![]() Directory listing is available with VSIReadDir(). zip as a directory, you can use /vsizip/path/to/the/file.zip or /vsizip/path/to/the/file.zip/subdir. To point to a file inside a zip file, the filename must be of the form /vsizip/path/to/the/file.zip/path/inside/the/zip/file, where path/to/the/file.zip is relative or absolute and path/inside/the/zip/file is the relative path to the file inside the archive. vsizip/ is a file handler that allows reading ZIP archives on-the-fly without decompressing them beforehand. Notable exceptions are the netCDF, HDF4 and HDF5 drivers. ![]() The full list of these formats can be obtained by looking at the driver marked with ‘v’ when running either gdalinfo -formats or ogrinfo -formats. ![]() Virtual file systems can only be used with GDAL or OGR drivers supporting the “large file API”, which is now the vast majority of file based drivers. (But when writing documentation please still use two.)) Drivers supporting virtual file systems (Note is also OK to say /vsizip/vsicurl/… with a single slash. zip # ogrinfo a shapefile in a zip file on an ftp: ogrinfo - ro - al - so / vsizip // vsicurl / ftp : // user : password. com / OSGeo / gdal / master / autotest / ogr / data / shp / poly. # ogrinfo a shapefile in a zip file on the internet: ogrinfo - ro - al - so / vsizip // vsicurl / https : // raw. ![]()
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