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GIS Tool in Drupal PNW Drupal Summit - Seattle October 20th, 2012. Mack Hardy & Tom Nightingale @AffinityBridge. History of Maps with Drupal Tools. Location Module, proximity and filter. Storage and Import. Storage - GeoField. Where do we store data in drupal? A common field format

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GIS Tool in DrupalPNW Drupal Summit - Seattle October 20th, 2012

Mack Hardy & Tom Nightingale

@AffinityBridge





Storage - GeoField

  • Where do we store data in drupal?

  • A common field format

  •  for geodata

    • WKT

    • Lat Lon

    • Bounding


Spatial Import    

How do we import data from external sources?

Shapefiles

KML files

Uses GeoPHP and ogr2ogr

Spatial module ->  Saves as WKT -> Geofield

http://drupal.org/project/spatial


ogr2ogr    

Wrapper module for the GDAL ogr2ogr library

- Spatial module calls ogr2ogr

- Converts data from source formats to WKT

http://drupal.org/project/ogr2ogr



Sync_PostGIS Module

  • Allows drupal to query PostGIS as a spatial query service, much in the way SOLR is used for search

  • Syncs data from Drupal entities with geofields to PostGIS

  • Provides query methods for testing intersection, within, buffer conditionshttp://drupal.org/project/sync_postgis



What does sync_postgis tell us?

Intersections with other data points

Within a buffer of 5km 


Testing for Intersection

function geoquery_intersects($item1, $item2) {

  $params = array($item1, $item2);

  foreach ($params as &$param) {

    if (is_scalar($param)) {

      $param = array('entity_type' => 'node', 'eid' => $param);

    }

  }

  if ($connection = sync_postgis_get_postgis_connection()) {

    $geo_query = new syncPgQuery($connection);

    return $geo_query->booleanRelQuery('intersects', $params[0], $params[1])->execute();

  }


Testing for Buffer Distance

function geoquery_dwithin($item1, $item2, $distance = 0, $srid = 4326) {

  $params = array($item1, $item2);

  foreach ($params as &$param) {

    if (is_scalar($param)) {

      $param = array('entity_type' => 'node', 'eid' => $param);

    }

  }

  if ($connection = sync_postgis_get_postgis_connection()) {

    $geo_query = new syncPgQuery($connection, $srid);

    return $geo_query->booleanRelQuery('dwithin', $params[0], $params[1], $distance)->execute();

  }

}


Displaying the results

With the results from the PostGIS backend, we can show the user useful information

In this case they know that 

- target is in the protected area

- target intersects 2 traplines 

- target is within a 5 km buffer of 4 other nodes of interest 



Beyond Vector Based Maps

We want to show huge datasets, the vector model requires "painting" the data onto the map, which is computationally expensive

Pre-rendering the dataset onto a tile, means the client can load the data quickly, and tiles are easy to cache

Obvious downside of caching, is that it doesn't work well with frequently changing data

Tilemill has been great for creating base tiles, but regenerating the entire tileset when the data changes is hard and time consuming


Comparing Vector vs MB Tiles

Vector - 2.30 MB of transfer - Client side render

Tiles - 529 kB of transfer - Server side render


Tilestache    

Python application for serving tiles 

tilestache takes inputs of : 

--- mbtiles which are pre-generated 

--- mapnik configuration (to generate tiles on the fly)

--- vector (geojson, arcjson) 

--- combinations of these inputs as composite

We are generating using mapnik with PostGIS as a datasource 

- provides a caching layer for serving tiles


Composite maps from PostGIS Data

  • base map satellite images

  • tilestache provides the data layers from PostGIS via mapnik

  • leaflet map definition points to layers in the layer switcher

Image credit http://mike.teczno.com/notes/tilestache.html


WAX interactivity

  • parcel data with tiles in JSON

  • on mouseover and on click behaviours

  • need to pre-cache WAX styling 




WAX interactivity

How UTF8 grid works

http://mapbox.com/demo/visiblemap/





Search API

Next we want to be able to return data items from SOLR  to a map

Search on non-geographic facets - just like a view

Search on geographic facets - facet controls pull data from PostGIS, or use SOLRs spatial extensions 

http://drupal.org/project/search_api_location


Discussion

[email protected]

http://affinitybridge.com


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