What is GIS/Spatial Programming? Important GIS/Spatial Terms Tools in the GIS/spatial stack How you get started What’s next?

1. GIS Applications in Ruby/Rails 101

2. Introduction

3. hence I love maps and mapping.
I work at Research Solutions Africa
(RSA) as a location analyst this is just
telling people more about a place that
they don’t know especially businesses.
On most platforms @kamalogudah
About Me

4. What I am Supposed to Do

5. What my Friends think I do

6. What My Boss Think I will Do

7. What I am doing

9. Agenda
 What is GIS/Spatial
Programming?
 Important GIS/Spatial Terms
 Tools in the GIS/spatial stack
 How you get started
 What’s next?

10. GIS in Ruby is Hard… Though possible
But

11. GIS?

12. Definition of Terms
• GIS: Geographical Information System
• Layers: just like the layers in Photoshop,
but they're georeferenced.
• Projection: algorithm for flatting the
globe
• Geometry: the core data type in a
Geospatial application

14. Spatial Programming?

15.  Exposing physical space as a first-order
programming concept.
 Has Rich, built-in support for shapes,
space, and the relationship of physical
objects to one another.
 Describes objects spatially eg Locations
on the earth, shapes of buildings etc.

16. Coordinate System
 Coordinate system defines the location
of a point on a planar or spherical surface.
 Geographic coordinate system is a 3D
reference system that locates points on the
Earth’s surface.
 A point has two coordinate values:
latitude and longitude which measure
angles.


17. Types of Coordinate System
1. Geocentric coordinate systems are 3D coordinate
systems with the origin located at the earth's center.
Geocentric coordinates measure X, Y, and Z distances
from the center of the earth.

18. Types of Coordinate System
2. Geographic coordinate systems are the familiar
latitude-longitude systems identifying points on the
earth's surface in terms of degrees. most common, eg
"WGS 84". used by GPS and most mapping apps.

19. Types of Coordinate System
 3.Projected coordinate systems involve taking a
portion of the earth's surface and "flattening" it.
Planar and generally Cartesian for easy display and
computation; introduces distortion.

20. Spatial Database

21. Spatial Data Types
Store shapes like points,lines, and
polygons in geometry columns.
Represents a binary representation of
a shapes in a db row (with location).

22. Geometry Hierarchy

23. Geometry

24. Spatial Functions
Spatial functions (in SQL) help query
spatial properties and relationships.
Normal Db has functions for
manipulating data in a query.
These include mathematical functions,
date, functions to work on Strings.
A spatial Db adds more to these “base
functions” these include those to operate
on geometries.

25. Spatial Functions
1. Conversion. Text representation of a point
(ST_AsText), (ST_GeomFromText).
2. Retrieval. Length of a road? (ST_Length),
perimeter of a Kenya (ST_Perimeter).
3. Comparison. Is Nairobi next to Turkana?
(ST_Touches), ST_Contains.
4. Generation. Calculate a 20km exclusion limit
around a point (ST_Buffer), Consolidate
Nairobi, Machakos, Kiambu and Kajiado
counties (ST_Union)

26. Spatial Index
Indexes make using a spatial db for
large data sets possible.
 Otherwise, any search for a feature
would require a “sequential scan” of
every record in the database.
 Indexing speeds up searching by
organizing the data into a search tree.
This can be quickly traversed to find a
particular record.

27. Indexing Example

28. R-Tree Hierarchy

29. Bounding boxes

30. PostGIS Anatomy.
 There are more than 700+ PostGIS functions.
 One table (spatial_ref_sys) and two views
(geometry_columns and
geography_columns).
 Spatial_ref_sys. Defines the spatial reference
systems known to the database (SRID).
 They are known by an ID number, such as
4326 (for WGS 84 Lat/Lon)

31. Geometry Columns
The geometry_columns view defines
the dimension, geometry, and spatial
reference system for each spatial table
in the PostGIS database that contains a
geometry type.

32. Geometry_columns

33. Geography Column
• The geography_columns view defines
the dimension, geometry, each spatial
table in the PostGIS database that
contains a geography type.

34. GIS STACK

35. 1. Database – PostgreSQL with
PostGIS extension (Preferably
and works).

36. Ruby
 rgeo --- a geospatial data library for Ruby.
 rgeo-shapefile --- RGeo component for reading ESRI
shapefiles
 rgeo-geojson --- RGeo component for reading and writing
GeoJSON
 Rgeo-activerecord –- is an optional RGeo module providing
spatial extensions for ActiveRecord.
 squeel --- ActiveRecord enhancement for query writing
 activerecord-postgis-adapter --- ActiveRecord adapter for
PostGIS
 ruby geocoder --- Integration with geocoding services

37. CLIENT SIDE
 heatmap.js --- A heatmap implementation for
Javascript
 thermo.js --- Another heatmap implementation for
Javascript
 heatcanvas.js --- Yet another heatmap
implementation for Javascript
 OpenLayers --- An open-source map/visualization
tool; an alternative to Google Maps.
 Mapbox, Leafletjs etc.

38. OTHERS
libgeos --- C library for geometric
analysis
libproj --- C library for coordinate
transforms
libgdal --- C library for rasters

40.  rails new rubyconf --database=postgresql

Create new app

 In Gemfile add activerecord-postgis-adapter

41. Configure Database
encoding: unicode
pool: <%=
ENV.fetch("RAILS_MAX_THREADS
") { 5 } %>
username: <your_username>
password: <your_password>

42. encoding: unicode
pool: <%=
ENV.fetch("RAILS_MAX_THREADS
") { 5 } %>
username: <your_username>
password: <your_password>
Configure Database

43. class CreateCountries < ActiveRecord::Migration[5.1]
def change
create_table :countries do |t|
t.string :name, :unique => true
t.string :iso_code, :unique => true
t.multi_polygon :geom, :srid => 4326
#t.timestamps null: false
end
change_table :countries do |t|
t.index :geom, using: :gist
end
end
end
Create Model

44. class CreateCountries < ActiveRecord::Migration[5.1]
def change
create_table :countries do |t|
t.string :name, :unique => true
t.string :iso_code, :unique => true
t.multi_polygon :geom, :srid => 4326
#t.timestamps null: false
end
change_table :countries do |t|
t.index :geom, using: :gist
end
end
end
Create Model

45. Importing Shapefile Data
def up
from_shp_sql = `shp2pgsql -c -g geom -W LATIN1 -s 4326
#{Rails.root.join('db', 'shpfiles', 'KEN_adm0.shp')} countries_ref `
Country.transaction do
execute from_shp_sql
execute <<-SQL
insert into countries(name, iso_code, geom)
select name_engli, iso, geom from countries_ref
SQL
drop_table :countries_ref
end
end
def down
Country.delete_all
End
end….

46. Importing Shapefile Data
def up
from_shp_sql = `shp2pgsql -c -g geom -W LATIN1 -s 4326
#{Rails.root.join('db', 'shpfiles', 'KEN_adm0.shp')} countries_ref `
Country.transaction do
execute from_shp_sql
execute <<-SQL
insert into countries(name, iso_code, geom)
select name_engli, iso, geom from countries_ref
SQL
drop_table :countries_ref
end
end
def down
Country.delete_all
End
end….

47. include Featurable
featurable :geom, [:name]
end
Alter Model

48. Featurable Module
Concerns/Featurable.rb
module Featurable
extend ActiveSupport::Concern
module ClassMethods
def featurable geom_attr_name, property_names = []
define_method :to_feature do
factory = RGeo::GeoJSON::EntityFactory.instance
property_names = Array(property_names)
properties = property_names.inject({}) do |hash, property_name|
hash[property_name.to_sym] = read_attribute(property_name)
hash
end
factory.feature read_attribute(geom_attr_name), self.id, properties
end
end

49. RGeo::GeoJSON::EntityFactory.instanc
e
features = models.map(&:to_feature)
factory.feature_collection features
end
end
end
Featurable continued

50. The End…