Census Mapping with GPS Natalie Dobbs Spatial Innovision

Census Mapping with GPS Natalie Dobbs Spatial Innovision Limited Tech@spatialvision. com 1

Overview • Case Study - Municipality of Rome • Introduction to GPS • Mobile GIS – Terrasync Workflow – Arc. Pad Workflow • Trimble Field Computers with GPS Receiver • Accuracy • Conclusion 2

Case Study MUNICIPALITY OF ROME: The Integrated Territorial System OFFICE OF STATISTICS AND CENSUS SERVICE OF TERRITORIAL DATA BANKS 3

Case Study: Field Activity • The main activities carried out in the field using portable devices include: a) Collection of field data: - Update of attribute information - Maps used as background images allowed visualisation of activity - GPS support enabled georeferencing of collected field information instantaneously. 4

Street Graphic Layers - Satellite Image 5

Case Study: Field Activity cont’d b) Field Inspections : - GPS enabled the collection of assets and resources (schools etc. ) 6

Case Study: Summary • Reliability of the information contained in the GIS has a key importance. • Data quality influences: - Specific planning and management of the area - Resulting in either a more or less positive result which is important to a local authority 7

Sphere of Influence of a School to Determine Demographic Capacity 8

What is GPS? • The Global Positioning System (GPS) is - Constellation of at least 24 satellites - Develop by the United States Department of Defense (Do. D) - Used worldwide by any civilian free of charge 9

GPS Segments • Divided into three segments 1) Control - Receives transmission & transmit information - Operated by the U. S. Department of Defense 2) Space - 24 satellites: - Orbit 20, 200 km above the Earth - 1 revolution in 12 hours 3) User - Utilized by many application of GPS to calculate GPS positions - Civilian use outnumber military use 10

Why We Use Satellites for Mapping • Line of Sight 11

Satellite Ranging • Measuring the distance from a satellite • Measuring travel time of radio signals Distance D = Time x Speed of light (300, 000 km/sec) 50 mil lise con ds il 0 m ds n o ec lis 4 12

Trilateration From Satellites • By measuring distance from several satellites you can calculate your position

Trilateration • One measurement narrows down our position to the surface of a sphere 11, 000 miles We're somewhere on the surface of this sphere.

Trilateration • Second measurement narrows it down to intersection of two spheres Intersection of two Spheres is a circle

Trilateration • Third measurement narrows to just two points

Trilateration • Fourth measurement will decide between two points

Source of Errors • Atmosphere Error - GPS signals are delayed as they pass through the atmosphere - The signals are delayed by the ionosphere and troposphere Ionosphere Troposphere 18

Source of errors cont’d • Multipath Error - Occurs when GPS signal is reflected off an object before it reaches the GPS antenna • Selective Availability - U. S. Department of Defense introduced artificial errors to reduce GPS position accuracy - Was largest source of error - Turned off May 2000 19

Source of Error cont’d • Obstruction 20

Differential GPS Two receivers track SAME signals and errors at SAME time 21

Comparing data acquisition technologies • GPS is one of many technologies – Manual digitizing of paper maps – Collection of attribute data with pen and paper – Scanned paper maps – Aerial photography – Satellite imagery – LIDAR or other 3 -D scan imagery 22

Comparing data acquisition technologies • GPS especially suitable for - Features where attributes only determined by field inspection - Features where other geocoding reference (e. g. street address) is absent - Integration with GIS as data is digital - Data where positional accuracy is critical to subsequent decision making - Navigation to and identification of assets by position - Scenarios where data use in the field is planned 23

Mobile GIS 24

Mobile GIS • Expansion of GIS technology from the office into the field • Integration of three essential components: - Global Positioning System (GPS) - Field Computer - GIS field software : - Data collection and maintenance - Arc. Pad and Terrasync • Two suggested workflow: - Terrasync workflow (Trimble) - Arc. Pad workflow (ESRI) 25

Field Software • Open platform to run the GIS software that you require • Support the data schema of GIS – Data dictionary or Native Shape files – Observe the domain rules of the GIS • Display raster and vector in the field 26

Terrasync Workflow Create Data Dictionary using GPS Pathfinder Office Software Transfer Data Dictionary using Data Transfer Utility Postprocess data in GPS Pathfinder Office Software Transfer Data Dictionary using Data Transfer Utility Terrasync Software on Field Computer with GPS Receiver Export to GIS or CAD format 27

Arc. Pad Workflow • Creation of a personal geodatabase • GPS- enable the personal geodatabase • Check out data from the Personal Geodatabse and transfer it to the field device • Collect data using Arc. Pad and GPScorrect extenion • Check in data to field computer • Process the imported GPS data with the use of GPS Analyst 28

Arc. Pad Workflow check out GPS Data Arc. GIS Arc. Pad GPS Analyst GPScorrect check in • Differentially correct • Query and analyze GPS data • Validate GPS position accuracy 29

Trimble Field Computers with GPS Receiver Post. Processed Accuracy Geo. XH Geo. XT Geo. XM Juno ST XB Edition XC Edition Subfoot <30 cm Submeter <1 m 1 -3 m 2 -5 m Everest Multipath Rejection Technology Yes No No H-Star Technology Yes No No No Bluetooth Yes Yes Yes Integrated wireless LAN & Trim. Pix technology Yes Yes Yes Windows Mobile 5 Yes Yes Yes 30

Trimble Field Computers with GPS Receiver Cont’d Geo. XH Geo. XT Geo. XM Juno ST XB Edition XC Edition 512 MB 128 MB 2 Compac t. Flash slots 1 Compac t. Flash slots Logging Memory 512 MB Expandable Memory 1 SD slot Battery Life 9 hours 6 hours 8 hours Ruggedness Withstan ds 1 m (3. 2 ft) drop Withsta nds 1 m (3. 2 ft) drop Nonrugged Withsta nd 1. 2 m (4. 4 ft) drop Recon handhel d: withsta nds 1. 2 m (4 ft) drop 31

GPS requirements – Accuracy in the Office • What analysis will be made with the data? To uniquely identify dwelling requires 3 m GPS accuracy Digging up a pipe requires <30 cm GPS accuracy • What is the accuracy of other GIS layers? 32

GPS requirements – Accuracy in the Field • When do you need the accuracy? – Navigation – In-field verification of position • Real-time Differential GPS 33

GPS requirements Accuracy • When do you need the accuracy? – Office based spatial analysis – Map making • Post-processed Differential GPS 34

Where do you need to be? 12 m 1 m 1 cm 1/2 cm 2 m 50 m 35

GPS requirements – field ready • All day battery • Temperature range – 50 degrees Celsius or greater • Outdoor viewable screen Depending on terrain • Ingress Protection (IP) – Water and Dust proofing • Rugged and hard wearing – Drop, shock and vibration proof 36

Summary • When planning GPS data collection consider – what accuracy you really need and when you need it – the day to day conditions such as heat and dust and rough treatment of equipment – the GIS field software that can be used on the device • GPS is an established and proven technology used worldwide for GIS data collection – Allows better decision making at a lower cost than traditional data acquisition techniques 37

Thank You SPATIAL INNOVISION 38