200307 Newsletter

QUEENSLAND BUSHWALKERS CLUB Newsletter

74 Kallista Rd. Rochedale South QLD 4123 Email [email protected] Phone No (07) 3341 7509 www.geocities.com/qldbwc

July 2003

FMR Training at Mt Barney

Club News Rogaine Competition

17-18 May

The Dark Side of the Moon Rogaine was held on private property near the base of Mt Greville not far from Aratula. It was run by the Qld Rogaine Club and 9 QBW club members participated in 3 separate teams. The 6 hour event started at 12 noon. All teams received their maps at 10am so there was time to work out a course to follow that would hopefully maximise points earned. It was very hilly terrain with lots of fences and some areas out of bounds. Most of the high point controls were on the tops of hills so we climbed up and down hills for 6 hours. We were not allowed to climb over fences so all had to be negotiated by rolling, sliding or slithering under the best and fastest way possible. I lost count of the fences; it seemed like every 10 minutes there was another one blocking our way. Some of the controls were in gullies, some on creek junctions, the easiest being at a road intersection. All 3 teams made it home to the Hash House by 6pm, one team with only seconds to spare. Every minute over time is penalised by losing points. Dinner, breakfast and camping are included in the entry fees. While none of our teams were amongst the winners we all enjoyed the competition and we're looking forward to the next one to be held on July 12 at Gatton. Barbara

Training Weekend

24-25 May

The Training Weekend at Mt Barney Lodge run by Federation Mountain Rescue (FMR) turned out to be a great success. There were talks, slide shows, presentations, demonstrations and practical exercises. Eight members of QBW attended and three of our members were speakers at this yearly event. FMR is an autonomous group associated with bushwalking clubs. It promotes safe walking and is trained and available for search and rescue operations in rugged bush and mountain terrain in south east Queensland. The Training Weekend is run every year and this year there was a wide range of topics and much hands on experience. A mini rescue had participants using radios and learning the different types of searches. A map and compass exercise had everyone thinking while a session on ropes had everyone in knots. The weekend was made more pleasurable by perfect weather and magnificent views of Mt Barney. Among the many speakers were three of our own members, David, Frank and Richard. Many thanks to the organisers for a very informative weekend.

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Richard

Campsite Monitoring

General Information

18 May

Once a year there is a meeting of the campsite monitors with the rangers. 16 monitors showed up at Daisy Hill Koala Centre and met with the rangers from Lamington, Main Range and Mt Barney National Park. Each monitor gave a talk on the state of the campsite they were looking after followed by a talk from the rangers. The rangers stated that the campsite monitoring process was yielding impressive data which was being shared with other national and international rangers. For me it was a great opportunity to meet the rangers and desk staff face to face. I had talked to with some of them quite a few times on the phone but had never met them personally. A special thanks to Vanessa at the Green Mountains Lamington National Park office who has always been helpful in requests for camp site bookings. Campsite monitoring has now been going on for ten years and the main purpose is to monitor the state of the camping area and try to determine if the area is being overused. It is supplying information about various factors which could affect the degradation of the campsite. The number of people using a campsite was a factor but not the only one as other things such as location, accessibility and surrounding vegetation played a role.

Membership Membership is still only $20 per year. Visitors pay $5 per walk for the first two walks to become a temporary member. On the third walk the remainder of the membership fee must be paid. Due to Insurance demands, a visitor must become a member on the 3rd walk.

Meeting Place General Meetings are held on the first Tuesday of each month at the East Brisbane State School, corner of Stanley Street and Wellington Road, starting at 7:30pm. There is parking within the school grounds off Wellington Road. Consult a street directory, as there are a number of one-way streets in the area. Tea/Coffee and cake/biscuits provided after the meeting.

Equipment for Hire The Club has a backpack (suitable for use as a day or through pack) for hire at $5.00 per week. QBW is also looking at purchasing further equipment in the near future. Any suggestions for equipment to buy would be appreciated. Also any person who has surplus equipment and would like to donate or sell to the Club, please contact Steve Moyle on 3800 3963.

At present eight members of QBW are involved with campsite monitoring. Richard and Gary look after the Running Creek campsite; Ed and Barbara, Ratatat Hut, Kerry and Trevor; Mt Throakban and Christine and Cliff Mt Superbus and Spicers Peak. A big thanks to these members who are assisting the National Parks look after our natural resources. Also thanks to Ann Tracey who is the main co-ordinator for the campsite monitors. Richard

Coming and Goings At a recent coffee night two of our members who have been away recently were there to tell us of their trips. Larapinta Trail John had done a 15 day walk along the Larapinta Trail in the Northern Territory. The walk was from the Old Telegraph Station to Mt Sumner, a distance of 232 kilometres. A vehicle was used as back up most of the way but there was one section where everyone had to carry eight litres of water plus sleeping bag and other gear. Despite it being in the hottest part of Australia, night temperature went down to –2 degrees Celsius! New Zealand and South America Another traveller was Fran who had been three months overseas. She spent two weeks in New Zealand walking the Routebourn and Greenstone Tracks with her daughter. Then off to South America for eight weeks to travel through Chile, Peru, Bolivia and Ecuador. Highlights were the Galapagos Islands, Nazca Lines, Lake Titicaca and the Inca Trail. A stay in Paris rounded off the trip.

Editors Pic

Bivy Bag/Pack Liners for Sale The Club has purchased a quantity of pack liners from VicWalk suitable for through packs. They are 2 metres by 0.9 metres in a bright orange colour. The packliners can double as an emergency bivvy bag and have helpful information printed on them. They are available from the Club for $3.00 each or 2 for $5.00.

The Management Committee For 2003 Secretary Treasurer Outings Secretary Membership Officer Social Secretary Training Officer Editor

Dianne Cox Linda Hellmuth Barbara Makepeace Steve Hill Paul Makepeace David Haliczer Richard Kolarski

3273 3484(H) 3395 0754(H) 3245 2186 (H) 0408 952 975 3245 2186 (H) 3879 8334(H) 3341 7509(H)

Other Voluntary Positions Equipment Officer Supper Convenor Federation Reps (2)

Steve Moyle Margaret Smith Richard Kolarski Margaret Smith David Haliczer Richard Kolarski

FMR Reps (2)

3800 3963(H) 3886 3342(H) 3341 7509(H) 3886 3342(H) 3879 8334(H) 3341 7509(H)

New Members Paula Bailey

Karen Bloomer

Amanda Geipel

Roslyn Kaiser

Cheryl Kidd

Geoffrey Kidd

Graham Walters Number of financial members

108

From the Editor Thanks to all who submitted articles and photos. Gnome away from Home

The deadline for articles for the August Newsletter is 29/7/2003. Page 2 of 6

Special Coming Events

Past Walks

Log Event - Team Navigation

Mt Edwards

Sunday 20th July

Mt Edwards is near Aratula on the Cunningham Highway and the start of the walk is across the dam wall at Moogerah Dam.

Meet at 8:00am at Mt May campsite. Suitable for "on-track" and "off-track" walkers able to walk 10km. Good for beginners, or anyone wanting to sharpen their navigation. Travel at your own speed. Where: Upper Portals area. Off track, but well-worn pads throughout the area.

13 April 2003

It is only a short walk and takes no longer than 3 hours to climb up the southern side of Mt Edwards, through the dry Iron Bark ridge to the cliffs at the northern end where the views back to Brisbane are worth the climb.

How:- Similar to a Rogaine. Pick your own team. Navigate a course from the instructions that will be handed out a week before the event. Hidden judges will ensure that you don't get lost and will score you for deviations from the course. Bonus points for bushcraft exercises along the way. Finish for lunch, where scores will be posted. Equipment:- Bring compass and day walk pack, lunch, water etc. A copy of the Mt Lindesay 1:25000 Topographic map would be very helpful. Contact Frank on 0419 715 719 for more information.

Salvator Rosa and Lonesome National Park

On top of Mt Edwards

Cliff & Christine Harrison who are experienced bushwalkers are planning two (2) extended trips. 1. Salvator Rosa National Park and Lonesome National Park (Expedition Range). Depart Brisbane: Saturday 31st August 2003. Back to Brisbane: Thurs 11th or Friday 12th September in time for the weekend annual Pilgrimage at Glen Rock. 2.

New Zealand - South Island

Those genuinely interested, please contact us by Email: [email protected] or Phone 5429 5494. Beginning September 22nd 2003 for two weeks. The walk begins and ends in Portland, Victoria, and is 250 km in its entirety but there is no place on the walk above 300m. The track is well graded and every campsite has a toilet and water tanks. For more information ring Richard Kolarski on 3341 7509(H)

Tasmania December 2003/January 2004 The itinerary for this trip to Tasmania is now finalized. 29 - 31 December 2003. Easy 3 day throughwalk on Freycinet Peninsula. 2 - 5 January 2004. Moderate to hard 4 day throughwalk in Pine Valley. 8 - 12 January 2004. Hard 5 day throughwalk South West Cape. 13 - 19 January 2004. Hard 7 day throughwalk South Coast Walk. You can come along for one, two, three or all of the walks above. The South West Cape and South Coast Walk involve a flight to Melaleuca from Hobart.

Garmont Boots NZ size 7½. Very little use. $100. Phone June 3863 4865 Scarpa Boots Size 8 Worn only twice $100 Phone Steve 3800 3963

18-21 April 2003

Lynn won the prize for the most exciting trip down with a detour into the scrub in her new car and Graham was almost given up for lost but finally arrived after dark.

Great South West Walk

FOR SALE

MacIntyre Falls Base Camp

A few of us drove down on Thursday afternoon, taking over six hours in the pre-Easter traffic, but the majority arrived Friday lunchtime. The campground had been re-sited a couple of years ago and is spread out beside the Severn River with plenty of space and trees dividing the area so our group had an area all to ourselves.

An 11 day through-walk in Nelson Lakes National Park. Depart Brisbane - Christchurch : Friday 13th February 2004 Back to Brisbane: Sunday 29th February 2004.

Contact Richard on 3342 7509 for more information.

Even though it is only a short walk it is worth the heart starter for the views. Six of us did the walk and dined at the summit. Ha needed more of a challenge so went on and climbed Mt Mitchell, while we decided Coffee at Aratula was more in line with our needs. Paul

A visit to the nearby caves was scheduled for the afternoon and filled in the time until happy hour. The stars came out and an almost-full moon followed. On Saturday morning we walked around to MacIntyre Falls with the intention of following the river down to the junction with the Severn River. However, after climbing down the falls, we found the water level too high to cross the river and the rock slabs alongside were too steep in places for us to traverse. So, rather than scramble up and over where necessary, we decided to change plans and head upriver instead. Dense scrub with heaps of cobbler's peg was found close to the river upstream making it difficult to find a pleasant spot for lunch. We finally settled for a small sandy patch with just enough shade for us all to rest. June went for a short walk another couple of minutes upstream and came back with tales of wide, open, slabby areas just around the corner. (How often does this happen?!!) So we packed up and went to see. We then headed cross-country in the direction of the road and followed it back to camp. Some brave souls went for a dip while others settled for a tent wash or camp shower. Linda found her car battery flat and the Ranger offered to take a message out to Ashford for RACQ help. Clean bodies gathered for another happy hour-plus and dinner another pleasant, fine evening. Easter Sunday morning and after visits by several Easter Bunnies we decided to walk off all the chocolate. Minus Linda (where is the RACQ?), we followed the road down to the junction of the MacIntyre and Severn where we climbed up a large slab for great

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views, then turned upstream along the Severn in the direction of our camp. Our destination was the Dungeon. Again we needed to go high to get around steep river banks. Some of it was quite exciting but again, crossing the river was difficult and no one keen to get wet feet or remove boots.

Boonoo Boonoo Falls

Once we started off in earnest up the creek though, it became clear that the gentle rock hopping we had expected was something a little more challenging, we were constantly "scouting" to find not just the best route through but any route through! By 12.30 we had made about 2kilomteres and it was becoming increasingly obvious that were not going to get through without a great deal of difficulty. We decided on a short lunch break to review the options: push on, retreat to last nights camp and follow the road, or tackle a steep but possible looking route out of the gorge (Blue Gully) then cross country to meet up with the road. 5 of us decided on the latter - whilst 2 decided to return to camp, drive to the locked gate (marked on the road) and meet with us there. We located Blue Gully (a little steeper than it appeared on the map - but isn't it always ?) and headed up. Estimates to reach the top ranged from 30-40 minutes, in fact we got up in 28 minutes, due to the fact that the sandstone rock was so crumbly, no one wanted to rest too long on a hold, Barb, Linda and myself, all taking short slides down the hill at some point.

MacIntyre Falls

We went as far as we could until lunchtime. A high detour was needed to continue to the Dungeon so we decided to eat and then head off on a bearing to take us back to the road and home. Linda's car had been fixed by midday and she had taken another road and visited the Dungeon, coming back with wonderful descriptions of the part of the river we almost reached. Another fine evening of socialising. Linda and Nadeen were up early to see sunrise and breakfasted on the cliff above the Dungeon. The rest of us arrived much later to enjoy the view before packing up and heading for home. Thanks to everyone who came along. It was a very pleasant, relaxing time and so amazing to have Easter without rain. Patricia

Boonoo Boonoo Falls T/W

3 - 5 May 2003

After nearly a yearlong layoff from through-walking - due in part to a knee injury sustained whilst playing tennis - I was tempted back by the thought of a gentle 3 day bush walk along the river as the walk was described in all of the information Barb, our walk leader could find. The 7 walkers (Lindsay, Lia, Barb, Linda, Peter, Neil and me Wanda) met for dinner at The Criterion pub in Warwick early Friday evening. It was a good way to kick off a May Day bush walk, and from there we all quickly fell into relaxation mode, as we made our way in convoy to our overnight camp (Undercliffe Falls). Morning dawned bright and clear, a longish car shuttle was required - so whilst the guys organized the cars - the girls did a quick recce of Bookookarara creek below the falls. It was a little scrubby - but as the ranger had said - "stay in the creek and you will be fine" we determined that this would be the way forward. The alternative was a 4WD track, both lead to our planned campsite at the junction of the Boonoo Boonoo River and Bookookarara Creek.

Locating the road once we gained the top was easy - finding the locked gate was not. We summited near a dam - not located on either of the 2 maps we had with us. Our search for the gate however, rewarded us with a close sighting of a magnificent Wedge Tailed Eagle perched on a fence post. Eventually we left a note for the others by a cattle grid and continued on. The 4wd track was a horror, all loose crumbly rocks with the last 3 kms a very steep descent. The first grumbling started to come from my knee! Our camp was very attractive close to an old hut and near a creek, with great swimming holes to wash away the day's aches and pains. That night we all consoled ourselves with the thought that in spite of today's unexpected " toughness" tomorrow would definitely be a gentle walk along the creek. It was such a lovely evening that Barb decided to test out the versatility of the orange plastic bags, as a bivvy bag - and sleep by the fire. We awoke to very heavy dew - fly's of tents were all soaking, whilst the orange bag had kept Barb dry, her sleeping bag outer was pretty wet with condensation. Getting wet was the order of the day as no sooner had we set off than we reached the first creek crossing! Expecting a rough track (from the walk information) we had planned to cover quite a few kilometers to ensure we only had a short walk out on the last day but the purported path along the creek, only ever materialized briefly. We were mostly scrambling, rock hopping climbing and crossing. I could leave out the bit where I fell half way through a creek crossing, but as there is photographic evidence of me being hauled to my feet I had better mention it! Whilst parts of the walk were attractive much of it was through " farmed land" and it lacked the wilderness attraction of most through - walks. Camp that night however was in a lovely spot, a soft grassy area; with a swimming hole we nicknamed the Hollywood spa and shower. Whilst the pink team members pampered their tired bodies in Hollywood the blue team chose to heat their water over the fire in an old tin bucket we found nearby!

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We planned to start the last day with a swim followed by breakfast on the rocks, bathed in morning sunlight, but like other aspects of this walk the weather refused to cooperate and we awoke to clouds. My knee had also swollen to 3 times its normal size, earning me the nickname of "hoppy" for the remainder of the trip. My thanks to my fellow walkers who took some of my load and lent me a second stick and compression sleeve to help me complete the walk. Whilst the last day was the most attractive walking, I probably don't need to say that it did not turn out to be "gentle" either! It took us five hours to complete the last six kilometers, detours for snakes - two browns and a black, included! The arrival at the base of Boonoo Boonoo Falls was however spectacular, one of those "making it all worthwhile views," and we were pretty much home weren't we? Just 50metres past the base of the falls was a track to the top, except we had to find the track! We encountered the worst scrub bash of the trip followed by a grade 8 rock climb before we finally located it!

GPS The hardest part in writing an article like this isn't deciding what to include but rather what to leave out. Every effort has been made to ensure the accuracy of information given, but there is always the risk, in trying to simplify a complex topic, that you might leave the wrong bits out. If you want to read more there are innumerable good books. If you have access to the internet you might look at the Geoscience Australia site http://www.ga.gov.au/ Introduction This article gives an overview of GPS and map datums, important concepts in understanding GPS. Navigation will be dealt with in subsequent articles. Like Teflon frying pans and the internet, GPS had its origins in United States military research and has now been embraced by users all over the world.

One last surprise was in store for us as we reached the top of the waterfall, a National parks photographer asked us to add authenticity to the photographs he was taking. As we posed looking out over the falls along the creek where we had walked it all looked so gentle!!

Love or hate the idea, the use of GPS in outdoor activities is exploding. Many bushwalkers see a GPS as cheating, circumventing the time needed to learn to navigate properly. It also sticks in some peoples craw that a machine can locate them more accurately than their own bearings.

My thanks to all participants for making it fun.

Certainly no one should go into the bush with out a sound knowledge of map and compass. There are plenty of circumstances where a GPS can let you down. But there is no escaping the positive side of carrying a GPS. Units are now available for less than $300 and weighing no more than 200 grams (about half the weight of a first aid kit).

Mt Walsh Base Camp

Wanda

3 - 5 May 2003

Three days of beautiful blue skies over the May long weekend greeted the lucky 13 members of QBW who went to the GetTogether at Mt Walsh organized by the Maryborough Bushwalkers Club.

A GPS can give an accurate fix if a member of a party is injured and someone needs to go for help. It can assist the search party with bearings. In a white-out it could be the difference between a warm hut and a survival situation. In surveying new routes it can provide fixes. It can avoid rescues by allowing lost parties to guide themselves out. I know of one search and rescue where the leader broke a leg and the team who went for help were poor navigators and got lost. The leader was rescued the next morning but it was two days before they found the others. The biggest down side to GPS in my mind is that it opens up wilderness areas to inexperienced and uncommitted walkers. That is a subject outside the scope of this article. How does it work? What weighs around a tonne, is 5 metres across and gets along at something like 2.6 kilometers per second?

On top of Mt Walsh

On the Saturday there were a variety of walks but I chose an easy stroll up Waterfall Creek. It had rained the previous few days so the creek was running merrily. Only one brave person went for a swim at our lunch spot. There was a harder walk for the next day. It was a climb to all of the three pinnacles, Dinosaur's Head and the top of Mt Walsh. It started with a flat stroll to the base of Mt Walsh and then a stiff walk to some cliffs. We negotiated our way up an exposed area and made it to the first pinnacle. From here we had an impressive view of the surrounds but more was to come. The second pinnacle was easy but to get to the very top of the third everyone needed a hand up over an immense boulder. The views were stunning. A short distance away was Dinosaur's Head but we had to descend first and then back up to get to it. The scramble to the top of this feature was tricky requiring the use of a nearby tree. Again the views more than made up for the effort. After lunch and a short rest we made our way to the summit of Mt Walsh. We contoured round to the main tourist track and it was an easy scramble to the top where we took our time enjoying the scenery. We returned back to camp after a long but fulfilling day. On the Monday we drove round to Coongarra Rockpool. It was only a short walk but we spent a few hours either swimming or exploring the surrounding area. Many thanks to the organizers for a great weekend.

Richard

The answer is, any one of the 24 NAVSTAR satellites sitting 20,000 kilometres out in space which feed the information used by your GPS receiver. The satellites are constantly moving and are in six different orbital paths, each making two complete orbits around the Earth in just under 24 hours. Each satellite transmits a signal which contains a variety of information including its I.D. code, status, position in the sky and the date and time the signal was sent. A GPS unit is little more than a fancy radio receiver, albeit one capable of receiving a signal from a satellite 20,000kms away! To determine your position the GPS receiver compares the time the signal was sent by the satellite with the time it was received by the GPS receiver. The time difference tells the GPS receiver how far away that particular satellite is. Time accuracy is crucial, even an error of a fraction of a second could give a reading that is miles out. The satellite uses an atomic clock, your GPS receiver maintains and corrects its own internal quartz clock using the orbiting satellites as a reference. If we take distance measurements from a minimum of three satellites, we can triangulate our position and the GPS receiver can determine a two dimensional position fix in a similar way to how you triangulate bearings on a map. With four or more satellites, a GPS receiver can determine a three dimensional position which includes altitude. You should note however that

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the Australian Height Datum (AHD), which is used on maps will vary slightly from GPS altitudes. By continuously updating the position the GPS can calculate your speed and direction of travel. Datums The point in space that the GPS locates by means of triangulation is only half the story. We now need to convert this position, expressed in geodetic coordinates to one expressed as a grid reference in relation to some point on the surface of the Earth. Long before GPS, the need to identify positions led to the UTM grid shown on most topographic maps. This isn't given in relation to the corner of an individual map, but relative to a predefined datum, a framework that enables us to define coordinate systems. Despite the existence of a flourishing Flat Earth Society most people will agree that the Earth is a sphere spinning through space. What the "round Earthers" aren't telling us is that in reality our planet is a biaxial ellipsoid, a three-dimensional figure generated by rotating an ellipse about its shorter axis. In layman's terms the Earth is a sphere that has been just a little bit squashed. Not too much, but the radius at the equator is about one third of one percent bigger than the radius at the poles, about 21 kilometers. What's more the Earth is a crinkly piece of real estate with bumps and hollows marking its surface. The highest mountain peaks are close to 9 kilometers above sea level and the deepest ocean trenches about 11 kilometers below it. Navigation and mapping instruments need to model this shape mathematically. In the past mapping agencies in each country would select an ellipsoid (Earth shape) that best represented the shape of the Earth for their region. These shapes were similar but not the same, and they were not geocentric, that is, the center of the ellipsoid used by Australia didn't match that used for say England, and neither of their centers matched the point deemed to be the centre of the Earth - a model known as World Geodetic System 1984 (WGS84). In Australia most maps produced prior to 1999, used the Australian Geodetic Datum 1984 (AGD 84). The Australian Geodetic Datum was proclaimed in the Australian Commonwealth Gazette of 6 October 1966. This proclamation included the parameters of the local ellipsoid, known as the Australian National Spheroid (ANS), which defined the adopted size and shape of the Earth, and the position of the origin point Johnston Geodetic Station. The adoption of this origin and best fitting local ellipsoid meant that the centre of the Australian National Spheroid (ANS) (which was designed to be the best estimate of the Earth's shape around the Australian continent rather than the world), did not coincide with the centre of mass of the Earth but lay about 200 metres from it. The Australian Geodetic Datum (AGD) has now been superceded by the Geocentric Datum of Australia (GDA), a new and more accurate Australian coordinate system based on an ellipsoid known as GRS80. A driving force behind this change was so that we can use the Global Positioning System (GPS) more easily. GPS is based on a geocentric datum known as the World Geodetic System 1984 (WGS84) whose center corresponds with the center of the Earth. The WGS84 is very similar to the GRS80. They have a small difference in the definition of their ellipsoid parameters but generally may be treated as the same. To use WGS84 coordinates here in Australia with the old AGD66/84 datum meant converting coordinates. The introduction of the GDA94 eliminates the need for a complex conversion as the coordinates read will be the same.

Definitions To help avoid confusion lets define some of those terms: Australian Geodetic Datum (AGD66 or AGD84); the map datum in use up to 1999. Australian Map Grid (AMG66 or AMG 84); the map grid based on AGD84. Australian National Spheroid (ANS); best fitting local ellipsoid used for AGD84. Geocentric Datum of Australia (GDA94); the map datum now in use. Map Grid of Australia (MGA94); the map grid based on GDA94. Geodetic Reference System (GRS80); the ellipsoid used to define the GDA94. World Geodetic System 1984 (WGS84); the reference system used for GPS. In a nutshell If that is just a little too complicated then the essence of it is that you need to look at the information on your map. Coordinates on maps based on GDA94 / MGA94 will shift by approximately 200m to the north east compared to maps based on AGD84 / AMG84 (the old system). For the old system you need to set your GPS for the AGD84, for the new system you need to set your GPS for WGS84. To find out how consult your GPS user manual. In most cases the GPS you buy will be preset on the WGS84 datum. If so the GPS position may differ by 200 metres from the map position for the bulk of maps currently in circulation. Most of us have a considerable investment in older maps and maps based on the AGD will remain on the map-shop shelves for a long time yet. They will still be useful, so long as you understand the differences. Accuracy There are two broad uses for a GPS: The first is logging a waypoint for future use e.g. where we left the car, so there will be no problem finding our way back to it, or a series of waypoints to outline a route (a straight line is rarely practical). Once the waypoint is entered, the GPS can tell us its bearing and distance. The second use is to get a set of coordinates that we then plot on a map. So what can go wrong? The GPS fix could be incorrect. All GPS fixes have some error, be it centimeters or metres. Possible errors include: There is a dithering factor (called selective availability) built into the system that introduces and error of up to 100m (in less than 5% of cases up to 300m) this is currently turned off but it could be turned on at any time. For civilian use the system only offers +/10m accuracy, even with selective availability turned off. The satellite's signal may bounce off particles in the atmosphere, which creates a slight time delay to the receiver. Since the receiver is comparing the time stamp provided by the satellite with its own record of time, any slight delays will add an error to the triangulation result. Signals may also bounce off buildings, mountains, and other large objects before reaching your GPS receiver, increasing the amount of travel time. Also large objects can blanket the signal, thick forests, valleys, the inside of buildings and vehicles are examples of places where you may not get a fix. Your plot on the map is also only as good as the map, as mentioned previously the GPS must be set to the correct datum, but also topographic maps only guarantee a certain accuracy, this is marked on the map, normally +/- 10m.

Because the center for the new system coincides with the center of the mass of the Earth, the shift to GDA means that all coordinates will shift by approximately 200m to the north east.

There are also some maps such as sketch maps and special event maps that have their own grid system. Maps used in some rogaining events for example may use their own grid specifically to discourage people from cheating by using a GPS.

All future Australian map production will be based on the GDA94.

To Be Continued

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Trevor Smith