Has the river changed course, or are my coordinates wrong?

A workshop to overcome spatial data confusion

Sara Johnson, Waterwatch Victoria

4th National Waterwatch Conference, February 2004

Spatial Data Workshop Overview

• Introduction

• Video, overview and Q&As

• GPS Activity - find the chocolate booty!

• Discussion - What does the new GDA mean for Waterwatch?

Introduction

• 3 minute discussion with a partnerFind out -

• Neighbour’s name

•Have they ever collected coordinates off -Maps?

GPS?

•What is the most important thing they’re wanting to take away from the workshop

Video

• 10 minute video on the new GDA

Video Overview

Datum - a mathematical surface that best fits the earth

• 1966 - Australia adopted the Australian Geodetic Datum

• the AGD was the best early fit of the Australian region

• not compatible with satellite Global Positioning Systems

• 1994 - Australia adopted the Geocentric Datum of Aust.

• Implemented from 2000

• the GDA is compatible with rest of the world and GPS

Video Overview

The AGD and the GDA vary by approx. 200 metres, depending on location.

• Applies to both latitude/longitude and eastings/northings

What is the impact?

204m

AGD66 145o

AGD66 37o50’

Australian Geodetic Datum

GDA94 145o

GDA94 37o50’

Geocentric Datum of Australia

AGD vs GDA

Datum AGD GDA

Geographical Coordinates(latitude/longitude)

AGD66 GDA94

Grid Coordinates(Eastings/Northings)(Universal TransverseMercator projection)

AMG66 MGA94

AGD vs GDA cont....

Datum AGD GDAGPS Compatible? Not by default, but

can change GPS toread AGD. Otherwise,~ 200m difference thatwould need to beconverted to GDAusing software.

Yes. GPS useWGS84 as default,or the GDA can beselected manually.Either datum can beused.

Map Compatible? Old topographic mapsare AGD. Check mapmargin.

New maps(1:100000 and1:250000 maps) areGDA compatible.Larger scale maps –check in your state.Check map margin.

How significant is 200 metres?

On a topographic map, it’s a matter of scaleMap Scale GDA Map shift1:5 000 40 mm1:25 000 8 mm1:100 000 2 mm1:250 000 0.8 mm Negligible

On the ground, 200m may be the difference between:

• Rural and urban land use

• A creek and a paddock

• VIC and NSW!

Is everyone moving to GDA?

No, there is no requirement for organisations to move to GDA.

AGD - private organisations generating spatial data for their own use, not requiring external comparative spatial data.

GDA - government agencies and public organisations that use external spatial data, or supply data to external data users.

Where does Waterwatch sit?

How can I convert between AGD and GDA?

EASY! Use an online transformer

http://www.geom.unimelb.edu.au/gda94/

GDAit

Most states have a local govt agency/university link for a state-specific transformer.

• Check workshop summary notes for QLD/VIC/NSW link.

• Check state govt websites - some states have developed small excel converters that can be downloaded and installed onto desktop.

Global Positioning Systems (GPS)

GDA and GPS

You borrow a mate’s GPS and log a series of WW monitoring sites with a GPS. Does that mean the data is in GDA?

Yes, if the datum is either WGS84 or GDA. You must check the settings to be sure.

No, if the datum is anything but WGS84 or GDA

Eastings/Northings = UTM

Latitude/Longitude = hdddomm.mmm

Which projection/position do you need?

http://gislounge.com/ll/gps.shtml

Want to know more about GPS?

Many websites contain information and tips on how make the most out of a GPS

http://gps.faa.gov/FAQ/faq-gps.htm

Search GPS on Australian and international websites using a search engine (eg Google)

Eg.

5 Easy Steps to GDA...

1. Understand GDA• access GDA information sheets and websites

2. Inventory of spatial information• What spatial data have you got? Collected in which datum?

3. Transform data to GDA (if desired)• Clearly identify datum with all spatial data

5. Update products derived from digital data

4. Archive superseded AGD maps/data

Sara Johnson

Waterwatch Victoria - Science Coordinator

Arthur Rylah Institute

123 Heidelberg Vic 3084

(03) 9450 8748