Server side geo_tools_in_drupal_pnw_2012

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 - 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 conditions

http://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

mack@affinitybridge.com
http://affinitybridge.com

Server side geo_tools_in_drupal_pnw_2012

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