+
+ +
+

Network capabilities

+
+

New in version 7.0.

+
+

PROJ 7.0 has introduced, per PROJ RFC 4: Remote access to grids and GeoTIFF grids, the capability to work with grid files +that are not installed on the local machine where PROJ is executed.

+

This enables to transparently download the parts of grids that are needed to +perform a coordinate transformation.

+
+

CDN of GeoTIFF grids

+

Files are accessed by default through a CDN (Content Delivery Network), +accessible through https://cdn.proj.org, that contains Geodetic TIFF grids (GTG) +datasets which are mirrored and managed by the +https://github.com/OSGeo/PROJ-data/ GitHub project. +Files in the CDN are designed to be used by PROJ 7 or later, but any software +project wishing to use the CDN for shifting support are encouraged to +participate in the project and leverage the CDN.

+
+
+

How to enable network capabilities ?

+

This capability assumes that PROJ has been build against libcurl, and that +the user authorizes network access.

+

Authorizing network access can be done in multiple ways:

+
+
    +

  • enabling / uncommenting the network = on line of proj.ini

    • +

  • defining the PROJ_NETWORK environment variable to ON

    • +

  • or using the proj_context_set_enable_network() with a +enabled = TRUE value.

    • +
+
+
+

Note

+

Instead of using the libcurl implementation, an application using the PROJ +API can supply its own network implementation through C function callbacks +with proj_context_set_network_callbacks(). Enabling network use +must still be done with one of the above mentioned method.

+
+
+
+

Setting endpoint

+

When this is enabled, and a grid is not found in the various locations where +resource files are looked for, PROJ will then +attempt at loading the file from a remote server, which defaults to +https://cdn.proj.org in proj.ini. This location can be changed with +the PROJ_NETWORK_ENDPOINT environment variable or with +proj_context_set_url_endpoint().

+
+
+

Caching

+

To avoid repeated access to network, a local cache of downloaded chunks of grids +is implemented as SQLite3 database, cache.db, stored in the +PROJ user writable directory.

+

This local caching is enabled by default (can be changed in proj.ini or +with proj_grid_cache_set_enable()). The default maximum size of the +cache is 300 MB, which is more than half of the total size of grids available, +at time of writing. This size can also be customized in proj.ini or +with proj_grid_cache_set_max_size()

+
+
+

Download API

+

When on-demand loading of grid is not desirable, the PROJ API also offers the +capability to download whole grids in the +PROJ user writable directory by using the +proj_is_download_needed() and proj_download_file() functions.

+
+
+

Download utility

+

projsync is a tool for downloading resource files.

+
+
+

Mirroring

+

If you are able, you are encouraged to mirror the grids via AWS S3 command line:

+
aws s3 sync s3://cdn.proj.org .
+
+
+

If direct S3 access is not possible, you can also use wget to locally mirror the +data:

+
wget --mirror https://cdn.proj.org/
+
+
+
+
+

Acknowledgments

+

The s3://cdn.proj.org bucket is hosted by the +Amazon Public Datasets program. +CDN services are provided by the AWS Public Dataset team via +CloudFront

+
+
+ + +
+