Using GeoDjango for user participation in enriching web GIS systems Bo Zhao University of Florida...

Using GeoDjango for user participation in enriching web GIS systems

Bo ZhaoUniversity of Florida

July 15th, 2009

Requests

ID Function Item1 CGA assigned logins authentication &

Permissions2 User login ability3 User uploads shape file to server shapefile uploading4 User specifies layer symbology

spatial data customizing & management

5 User populates Layer List tab6 User defines layer searchability7 User defines attributes returned8 Files that are generated if adding new layer Spatial Crud & related

operation9 Files effected when layer is removed

So we need…

• Web Framework–PHP, ASP, Python, Java

• Geospatial libraries–Commercial Geospatial libaries, Open

Source libaries.

Why Python Matters?

• Glue Language• Dynamic script Language

Open Source Geospatial Libs

• Pros– Open source is very competitive for geospatial server

software– Reduced total cost of ownership– Possibility that you own your own software– Better preparation for computing trends.

• Cons– Limited technical support.– Adding Patches or updating might render to crash.– Possibility that you own your own software

Why Geodjango?

“Django is a high-level Python web framework that encourages rapid development and clean, pragmatic design.”

Features of Django Framework

• Object-relational mapper: Define your data models entirely in Python. You get a rich, dynamic database-access API, unnecessary to write SQL for query.

• Template system: Use template language to separate design, content and Python code.

• Automatic admin interface: Django does that automatically, and it's production-ready.

• Elegant URL design: Design pretty URLs with no framework-specific limitations. Be as flexible as you like.

• Cache system: cache frameworks for super performance.• Internationalization: Django has full support for multi-language

applications.

Design Pattern

MTVModel Template View

Object-relational mapping

• Object-relational mapping (ORM)– a programming technique for converting data

between incompatible type systems in relational databases and object-oriented programming languages.

– ORM creates, in effect, a "virtual object database" that can be used from within the programming language.

CREATE TABLE “hug_layer_world" (

"id" serial NOT NULL PRIMARY KEY,

"name" varchar(300) NOT NULL,

"geom" geometry NOT NULL,

CONSTRAINT hug_layer_world_pkey PRIMARY KEY (hug_fid),

CONSTRAINT enforce_dims_geom CHECK (ndims(geom) = 2),

CONSTRAINT enforce_geotype_geom CHECK (geometrytype(geom) =

'MULTIPOLYGON'::text OR geom IS NULL),

CONSTRAINT enforce_srid_geom CHECK (srid(geom) = 4326)

);

Scary Quirky Language

• SQL knows no version control

• Can be dangerous

• DRY(Don’t Repeat Yourself.)

from django.contrib.gis.db import models

class LAYERS(models.Model):

id = models.AutoField(primary_key=True)

name = models.CharField(max_length=20)

geom = models.MultiLineStringField(srid=4326)

objects = models.GeoManager()

SELECT"hug_layer_world"."id","hug_layer_world".“name","hug_layer_world".“geom"FROM ""hug_layer_world"WHERE "hug_layer_world"."name" = "China";

WORLD.objects.filter(title='China')

Template

DRY(Don’t repeat yourself)

index.html

<html><head><title>{% block title %}{% endblock %}</title></head><body>{% block content %}{% endblock %}</body></html>

tilecache.cfg

[{{layer.name}}]url = {{layer.mf_url}} layers = {{layer.name}}spherical_mercator = {{layer.tc_spherical_mercator}}extension = {{layer.tc_extension}}metatile = {{layer.tc_metatile}}srs = EPSG:{{layer.tc_srs}}type = {{layer.tc_type}}searchable = {{layer.tc_searchable}}… …

dataLayer.js

amTemplates.{{layer.name}} = '<ul class="featureDetailList">' +{% for item in layer.alias %} {% ifnotequal item.name 'geom' %} '<li><label>{{item.alias}}</label><span> {{layer.left}}{{item.name}}{{layer.right}}</span></li>' + {% endifnotequal %}{% endfor %}'</ul>';

/export.php?id=2&type=tilecache/upload.aspx?filetype=shapefile

/export/tilecache/world//upload/shapefile/

url.py

• (r'^admin/upload/', 'upload_zipped_shapefiles.upload_zipfile'),

• (r'^admin/export/$', 'export_config_files.index'),

• (r'^databrowse/(.*)', databrowse.site.root),

• (r'^map/(?P<path>.*)$', 'django.views.static.serve', {'document_root':

settings.MAPS_DIR, 'show_indexes': True}),

View functions

def index(request):all_layers = LAYER.objects.all()all_maps = MAP.objects.all()return render_to_response('export.html', {'layers': all_layers, 'maps': all_maps, 'user': request.user})

world/ __init__.py admin.py models.py views.py templates/ layer_javascript.html layer_tilechache.html layer_mapfile.html

Hands-on demo

Thanks, any questions?

References

• http://www.djangoproject.com/• Justin Bronn, Web Applications for (Neo)Geographers with

Deadlines, Oct. 2008• http://en.wikipedia.org/wiki/Object-relational_mapping

Using GeoDjango for user participation in enriching web GIS systems Bo Zhao University of Florida...

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