# NGW -- NextGIS Web

Driver short name

NGW

Build dependencies

libcurl

NextGIS Web - is a server GIS, which allows storing and editing geodata and to display maps in web browser. Also NextGIS Web can share geodata with other NextGIS software.

NextGIS Web has the following features:

- Display maps in a web browser (different maps with different layers and styles)

- Flexible permissions management

- Load geodata from PostGIS or import from GIS formats (ESRI Shape, GeoJSON or GeoTIFF)

- Load vector geodata in the following formats: GeoJSON, CSV, ESRI Shape, Mapinfo tab

- Import map styles from QGIS project or set them manually

- Act as a server for TMS, WMS, MVT, WFS

- Act as a client for WMS

- User can add photos to records, change record attributes via web interface or WFS-T protocol

NextGIS Web - is an open source software (license GPL v2+, see GNU General Public License, version 2).

## Driver capabilities

Supports Georeferencing

This driver supports georeferencing

## Driver

The driver can connect to the services implementing the NextGIS Web REST API. NGW driver requires cURL support in GDAL and WMS driver. The driver supports read and write operations.

## Dataset name syntax

The minimal syntax to open a NGW datasource is: NGW:[NextGIS Web URL][/resource/][resource identifier]

- NextGIS Web URL may be an URL to nextgis.com cloud service (for example, https://demo.nextgis.com), or some other URL including port and additional path (for example, http://192.168.1.1:8000/test).

- resource is mandatory keyword dividing resource identifier from the rest of URL.

- resource identifier this is positive number from 0 and above. This may be a resource group, vector, PostGIS or raster layer, style.

All vector layers, PostGIS, raster layers, styles will list as child resources if identifier is resource group. In other case this will be a separate layer.

## Configuration options

Configuration options can be specified in command-line tools using the syntax `--config <NAME>=<VALUE>` or using functions such as `CPLSetConfigOption()` (C) or `gdal.config_options` (Python). The following configuration options are available:

- NGW_USERPWD=value: User name and password separated with colon. Optional and can be set using open options.

- NGW_BATCH_SIZE=value: Size of feature insert and update operations cache before send to server. If batch size is -1 batch mode is disabled. Delete operation will execute immediately.

- NGW_PAGE_SIZE=value: If supported by server, fetch features from remote server will use paging. The -1 value disables paging even it supported by server.

- NGW_NATIVE_DATA=value: Whether to store the json extensions key in feature native data.

- NGW_JSON_DEPTH=value: The depth of json response that can be parsed. If depth is greater than this value, parse error occurs.

  > The depth of json response that can be parsed. If depth is greater than this value, parse error occurs.

- NGW_EXTENSIONS=value: Comma separated extensions list. Available values are description and attachment. This needed to fill native data.

- NGW_CONNECTTIMEOUT=value: Maximum delay for the connection to be established before being aborted in seconds.

- NGW_TIMEOUT=value: Maximum delay for the whole request to complete before being aborted in seconds.

- NGW_MAX_RETRY=value: Maximum number of retry attempts if a 429, 502, 503 or 504 HTTP error occurs.

- NGW_RETRY_DELAY=value: Number of seconds between retry attempts.

## Authentication

Any operations (read, write, get metadata, change properties, etc.) may require an authenticated access. Authenticated access is obtained by specifying user name and password in open, create or configuration options.

## Feature

If the `NATIVE_DATA` open option is set to YES, the extensions json object will store as a serialized json object in the NativeData property of the OGRFeature object (and "application/json" in the NativeMediaType property). If writing OGRFeature has NativeMediaType property set to "application/json" and its NativeData property set to serialized json object the new NGW feature extensions json object will fill from this json object.

Extensions json object structure see in NextGIS Web API documentation

## Geometry

NextGIS Web supports only one geometry column. Default spatial reference is Web Mercator (EPSG:3857). The following geometry types are available:

- POINT

- LINESTRING

- POLYGON

- MULTIPOINT

- MULTILINESTRING

- MULTIPOLYGON

Geometry with Z value also supported.

## Field data types

NextGIS Web supports only following field types:

- OFTInteger

- OFTInteger64

- OFTReal

- OFTString

- OFTDate

- OFTTime

- OFTDateTime

Driver stores additional field data in comment as JSON string:

- field identifier in NGW

- check if this is label field

- check to show field in grid view

- check to use field in text search

Driver supports alter field:

- name

- alternative name

- field domain

- comment

## Paging

Features can retrieved from NextGIS Web by chunks if supported by server (available since NextGIS Web 3.1). The chunk size can be altered with the `NGW_PAGE_SIZE` configuration option or `PAGE_SIZE` open option.

## Write support

Datasource and layers creation and deletion is possible. Write support is only enabled when the datasource is opened in update mode and user has appropriate permissions. Vector and PostGIS layers insert and update operations are cached if `BATCH_SIZE` is greater 0. Delete operation executes immediately.

## Open options

Open options can be specified in command-line tools using the syntax `-oo <NAME>=<VALUE>` or by providing the appropriate arguments to `GDALOpenEx()` (C) or `gdal.OpenEx` (Python). The following open options are available:

- USERPWD=value: Username and password, separated by colon.

- PAGE_SIZE=value: Defaults to `-1`. Limit feature count while fetching from server. Default value is -1 - no limit.

- BATCH_SIZE=value: Defaults to `-1`. Size of feature insert and update operations cache before send to server. If batch size is -1 batch mode is disabled.

- NATIVE_DATA=[YES​/​NO]: Defaults to `NO`. Whether to store the json extensions key in feature native data.

- JSON_DEPTH=value: Defaults to `32`. The depth of json response that can be parsed. If depth is greater than this value, parse error occurs.

- EXTENSIONS=value: Comma separated extensions list. Available values are description and attachment. This needed to fill native data.

- CONNECTTIMEOUT=value: Maximum delay for the connection to be established before being aborted in seconds.

- TIMEOUT=value: Maximum delay for the whole request to complete before being aborted in seconds.

- MAX_RETRY=value: Maximum number of retry attempts if a 429, 502, 503 or 504 HTTP error occurs.

- RETRY_DELAY=value: Number of seconds between retry attempts.

## Dataset creation options

Dataset creation options can be specified in command-line tools using the syntax `-dsco <NAME>=<VALUE>` or by providing the appropriate arguments to `GDALCreate()` (C) or `Driver.Create` (Python). The following dataset creation options are available:

- KEY=value: Key value. Must be unique in whole NextGIS Web instance. Optional.

- DESCRIPTION=value: Resource description. Optional.

- USERPWD=value: Username and password, separated by colon.

- PAGE_SIZE=value: Defaults to `-1`. Limit feature count while fetching from server. Default value is -1 - no limit.

- BATCH_SIZE=value: Defaults to `-1`. Size of feature insert and update operations cache before send to server. If batch size is -1 batch mode is disable.

- NATIVE_DATA=[YES​/​NO]: Defaults to `NO`.

  Whether to store the json extensions key in feature native data.

- JSON_DEPTH=value: Defaults to `32`. The depth of json response that can be parsed. If depth is greater than this value, parse error occurs.

- EXTENSIONS=value: Comma separated extensions list. Available values are description and attachment. This needed to fill native data.

- CONNECTTIMEOUT=value: Maximum delay for the connection to be established before being aborted in seconds.

- TIMEOUT=value: Maximum delay for the whole request to complete before being aborted in seconds.

- MAX_RETRY=value: Maximum number of retry attempts if a 429, 502, 503 or 504 HTTP error occurs.

- RETRY_DELAY=value: Number of seconds between retry attempts.

## Layer creation options

Layer creation options can be specified in command-line tools using the syntax `-lco <NAME>=<VALUE>` or by providing the appropriate arguments to `GDALDatasetCreateLayer()` (C) or `Dataset.CreateLayer` (Python). The following layer creation options are available:

- OVERWRITE=[YES​/​NO]: Defaults to `NO`. Whether to overwrite an existing table with the layer name to be created. The resource will delete and new one will created. This leads that resource identifier will change. Defaults to

- KEY=value: Key value. Must be unique in whole NextGIS Web instance. Optional.

- DESCRIPTION=value: Resource description. Optional.

## Metadata

NextGIS Web metadata are supported in datasource, vector, PostGIS, raster layers and styles. Metadata are stored at specific domain "NGW". NextGIS Web supported metadata are strings and numbers. Metadata keys with decimal numbers will have suffix .d and for real numbers - .f. To create new metadata item, add new key=value pair in NGW domain using the SetMetadataItem function and appropriate suffix. During transferring to NextGIS Web, suffix will be omitted. You must ensure that numbers correctly transform from string to number.

Resource description and key map to appropriate description and keyname metadata items in default domain. Changing those metadata items will cause an update of resource properties.

Resource creation date, type and parent identifier map to appropriate read-only metadata items creation_date, resource_type and parent_id in default domain.

Vector layer field properties (identifier, label field, grid visibility, text search) saved as json string in field comment.

Starting from GDAL 3.3 field alias can be set/get via SetAlternativeName and GetAlternativeNameRef.

## Domains

Driver supports only coded field domain. Since NGW does not support field types in domains, three domains are created for each domain where keys can be represented as numbers:

- domain_name with field type OFTString

- domain_name + " (number)" with field type OFTInteger

- domain_name + " (bigint)" with field type OFTString64

Deleting any of the three domains will delete the others.

Also NGW does not support null as coded values. So the null will represent as empty string.

## Filters

Vector and PostGIS layers support SetIgnoredFields method. When this method executes any cached features will be freed.

Vector and PostGIS layers support SetAttributeFilter and SetSpatialFilter methods. The attribute filter will evaluate at server side if condition is one of following comparison operators:

- greater (>)

- lower (<)

- greater or equal (>=)

- lower or equal (<=)

- equal (=)

- not equal (!=)

- LIKE SQL statement (for strings compare)

- ILIKE SQL statement (for strings compare)

Also only AND operator without brackets supported between comparison. For example,

    FIELD_1 = 'Value 1'

    FIELD_1 = 'Value 1' AND FIELD_2 > Value 2

In other cases attribute filter will evaluate on client side.

You can set attribute filter using NextGIS Web native format. For example,

    NGW:fld_FIELD_1=Value 1&fld_FIELD_2__gt=Value 2

Don't forget to add 'NGW:' perefix to where clause and 'fld_' prefix to field name.

Dataset supports ExecuteSQL method. Only the following queries are supported:

- DELLAYER: layer_name; - delete layer with layer_name.

- DELETE FROM layer_name; - delete any features from layer with layer_name.

- DELETE FROM layer_name WHERE field = value; - delete features from layer with layer_name and where clause.

- DROP TABLE layer_name; - delete layer with layer_name.

- ALTER TABLE src_layer RENAME TO dst_layer; - rename layer.

- SELECT field_1,field_2 FROM src_layer WHERE field_1 = 'Value 1' AND field_2 = 'Value 2';

In SELECT statement field list or asterisk can be provided. The WHERE clause has same limitations as SetAttributeFilter method input.

## Examples

Read datasource contents (1730 is resource group identifier):

    ogrinfo -ro NGW:https://demo.nextgis.com/resource/1730

Read layer details (1730 is resource group identifier, Parks is vector layer name):

    ogrinfo -ro -so NGW:https://demo.nextgis.com/resource/1730 Parks

Creating and populating a vector layer from a shapefile in existing resource group with identifier 1730. New vector layer name will be "some new name":

    ogr2ogr -f NGW -nln "some new name" -update -doo "BATCH_SIZE=100" -t_srs EPSG:3857 "NGW:https://demo.nextgis.com/resource/1730" myshapefile.shp

Warning

The -update key is mandatory, otherwise the destination datasource will silently delete. The -t_srs EPSG:3857 key is mandatory because vector layers spatial reference in NextGIS Web can be only in EPSG:3857.

Note

The -doo "BATCH_SIZE=100" key is recommended for speed up feature transferring.

Creating and populating a vector layer from a shapefile in new resource group with name "new group" and parent identifier 1730. New vector layer name will be "some new name":

    ogr2ogr -f NGW -nln "Название на русском языке" -dsco "BATCH_SIZE=100" -t_srs EPSG:3857 "NGW:https://demo.nextgis.com/resource/1730/new group" myshapefile.shp

## See also

- Raster side of the driver

- NextGIS Web documentation

- NextGIS Web for developers