This Page - GS20 sub-metre surveying

GIS data collection on a PDA- Leica GS5 and GS5+

The new DGPS- GIS data collection system from Leica

Post-processing data in a computer is a DGPS option. Accuracy will depend on method. 1. Leica GS20 post processed (0.3 metres) differential survey system You can collect data in Leica or Rinex format for post-processing by computer, with base station data. This is code L1 data, to around 0.3 metres. Occupation times on each point, is 2-5 minutes, to ensure most productive data, as there is no way of knowing position accuracy until after process. Base station data can be purchased from a third party supplier (usually government or university facilities), or using a second Leica unit to log corrections at a known point. If you are not purchasing a real-time system, we can supply with a battery and charger, and cost is around $8000 + GST for each unit. If you purchase one unit, you can use base station data from third party sources, using GISDataPro as the processing software, supplied. If you purchase 2 units, each GS20 can be used interchangeably, one as a base recording known position data, and the other used as the data recorder in the field. You can collect the data using the same methodology as in the real-time system, but you will need to stay on each point for 2-5 minutes to ensure that the point processes to within 1 metre, and maybe longer if you want 0.4 metres. You need to wait for the processed results to see accuracies obtained. You can always use the GS20 as a standalone data collector for 3-4 metre accuracy. 2. Leica GS20 post processed (1-5 cm) differential survey system: GS20 handheld can be used standalone without the real time accessories. If you are not purchasing a real-time system, we can supply with a battery and charger, and cost is $8000 + GST for each unit, plus a once only additional software lock for GIS DataPro of $2050 + GST, to enable phase processing. If you purchase one unit, you can use base station data from third party sources, using GISdataPro as the processing software, supplied. If you purchase 2 units, each GS20 can be used interchangeably, one as a base recording known position data, and the other used as the data recorder in the field. You can collect the data using the same methodology as in the real-time system, but you will need to stay on each point for 20-30 minutes to ensure that the point processes to within 1cm, and probably elevations less than 50mm. You need to wait for the processed results to see accuracies obtained. L1 phase and code data is used for processing. Base station data can be purchased from a third party supplier (usually government or university facilities), or you can use a second Leica unit to log corrections at a known point. This method requires an additional software module for GIS Data Pro. You can always use the GS20 standalone as a data collector for 3-4 metre accuracy.

There are three systems available to GS20 users for real-time DGPS. In the real-time method, this is sub-metre (around 0.4 metres), with occupation for a point, of around 30 seconds or less. Time is short because of real time monitoring of position accuracy. See further below for post-processed options. 1. DGPS using beacons such as the Australian AMSA (covers much of Australia's coastline and 300km inland), or the US Coast Guard (in the USA). This is called the RTB set. 2. DGPS using satellite differential signal from Omnistar. This has world-wide coverage, including Australia, PNG, Indonesia, SE Asia, China, India etc. Use in the remotest areas, no base station to set up. Perfect for preliminary surveys. This is called the RTS set. 3. DGPS using a local RTCM transmitter. Many mining companies and other utilities already have RTK GPS sytems that transmit a DGPS signal. The GS20 will fit perfectly in these situations for quick geological, or civil engineering pickup.

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