GIS Tool in DrupalPNW 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 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

Query 

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 conditions

http://drupal.org/project/sync_postgis

Sync_PostGIS Module

What does sync_postgis tell us?

Intersections with other data pointsWithin a buffer of 5km 

Testing for Intersectionfunction 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 Distancefunction 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 

Scaling

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

WAX interactivity

Demo

WAX interactivity

How UTF8 grid workshttp://mapbox.com/demo/visiblemap/

Random Tools

Leaflet Draw

Leaflet Paste

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

mack@affinitybridge.comhttp://affinitybridge.com