# NAS - ALKIS

Driver short name

NAS

Build dependencies

Xerces

The NAS driver reads the NAS/ALKIS format used for cadastral data in Germany. The format is a GML profile with fairly complex GML3 objects not easily read with the general OGR GML driver.

This driver depends on GDAL/OGR being built with the Xerces XML parsing library.

The driver looks for "opengis.net/gml" and one of the strings semicolon separated strings listed in the configuration option NAS_INDICATOR (which defaults to "NAS-Operationen;AAA-Fachschema;aaa.xsd;aaa-suite") to determine if a input is a NAS file and ignores all files without any matches.

The configuration option NAS_GFS_TEMPLATE makes it possible to cleanly map element paths to feature attributes using a GFS file like in the GML driver. Multiple geometries per layer are also possible (eg. ax_flurstueck.objektkoordinaten next to the regular wkb_geometry). Starting with GDAL 3.7, defining the NAS_GFS_TEMPLATE configuration option is required for the NAS driver to open a file. It may be set to the empty string to mean that the driver should try to establish the schema of the file from its content, but using one of templates mentioned below is recommended. Alternatively, starting with GDAL 3.10, specifying the `-if NAS` option to command line utilities accepting it, or `NAS` as the only value of the `papszAllowedDrivers` of `GDALOpenEx()`, also forces the driver to recognize the passed filename.

The GFS templates and PostgreSQL schemas are part of norGIS ALKIS-Import (also featuring a shell script and PyQt frontend which ease the import). There are currently two versions:

- GeoInfoDok 6: GFS template (for GDAL >=3.8 and <3.8) and PostgreSQL schema

- GeoInfoDok 7.1.2: GFS template and PostgreSQL schema

The files were generated using xmi2db (fork of xmi2db) from the official application schema.

In GDAL 3.8 the creation of the relation layer alkis_beziehungen was removed. Prior the configuration option NAS_NO_RELATION_LAYER allowed to disable its population - which was default in ALKIS-Import. The information found there was redundant to the relation fields also contained in original elements/tables. Enabling the option also made progress reporting available.

Duplicate data in datasets will usually causes errors. When importing separate datasets into PostgreSQL it is useful to enable `OGR_PG_SKIP_CONFLICTS` to skip conflicting features.

This driver was implemented within the context of the PostNAS project, which has more information on its use and other related projects.

## Driver capabilities

Supports Georeferencing

This driver supports georeferencing

Supports VirtualIO

This driver supports virtual I/O operations (/vsimem/, etc.)