Guidelines for the use of GNSS in surveying and mapping
Guidelines for the use of GNSS in surveying and mapping
Guidelines for the use of GNSS in surveying and mapping
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Table D3: Survey methods – dynamic real-time surveys<br />
Epoch separation Advantages Disadvantages<br />
20 sec or<br />
30 sec<br />
Dual-frequency receivers<br />
Forgiv<strong>in</strong>g, tolerates cycle slips<br />
Calculates effects <strong>of</strong> ionosphere<br />
Relatively long occupations<br />
Geodetic choke r<strong>in</strong>g or ground-plane antenna is needed<br />
Advanced process<strong>in</strong>g strategies required<br />
Advanced error modell<strong>in</strong>g required <strong>in</strong> process<strong>in</strong>g s<strong>of</strong>tware<br />
5 sec or<br />
10 sec<br />
Short occupations, very efficient<br />
No requirements <strong>for</strong> ma<strong>in</strong>ta<strong>in</strong><strong>in</strong>g lock between po<strong>in</strong>ts<br />
Requires dual-frequency receivers<br />
More susceptible to GDOP problems<br />
Requires careful plann<strong>in</strong>g <strong>and</strong> good communication <strong>in</strong> <strong>the</strong> field<br />
L<strong>in</strong>es limited to 40km<br />
1 sec Low-cost receiver<br />
Only s<strong>in</strong>gle receiver required<br />
More <strong>for</strong>giv<strong>in</strong>g <strong>of</strong> cycle slips<br />
Low level <strong>of</strong> precision only<br />
Long observation period required to obta<strong>in</strong> sub-metre position<strong>in</strong>g<br />
Need specialist process<strong>in</strong>g s<strong>of</strong>tware to get sub-metre accuracy<br />
1 sec or<br />
2 sec<br />
Very short occupations<br />
Most effective data collection<br />
One person can carry out survey<br />
Dual-frequency receivers – loss <strong>of</strong> lock does not ca<strong>use</strong> problems<br />
Logg<strong>in</strong>g <strong>of</strong> QC <strong>in</strong><strong>for</strong>mation to produce vectors <strong>for</strong> network adjustment, if<br />
required<br />
Must ma<strong>in</strong>ta<strong>in</strong> lock to 4 SVs while mov<strong>in</strong>g<br />
Must <strong>in</strong>itialise with 5 or more satellites<br />
Most susceptible to PDOP effects<br />
Dual-frequency receivers – requires high-end receivers <strong>and</strong> postprocess<strong>in</strong>g<br />
s<strong>of</strong>tware<br />
High equipment cost<br />
Requires rigorous QC <strong>and</strong> re-visits to static control po<strong>in</strong>ts <strong>for</strong> checks<br />
1 sec Low equipment cost<br />
Effective technique <strong>for</strong> GIS/asset location<br />
No real-time l<strong>in</strong>k required – cheaper <strong>in</strong>itial equipment cost<br />
Low level <strong>of</strong> precision<br />
Vectors not appropriate <strong>for</strong> network adjustment<br />
Cannot check accuracy values <strong>of</strong> data <strong>in</strong> field<br />
1 sec or<br />
2sec<br />
As <strong>for</strong> high-precision dynamic<br />
Real-time co-ord<strong>in</strong>ates are available<br />
As <strong>for</strong> high-precision dynamic<br />
Communications l<strong>in</strong>k between base <strong>and</strong> rover must be ma<strong>in</strong>ta<strong>in</strong>ed<br />
L<strong>in</strong>es limited to 15–20km. For Network RTK <strong>the</strong> service operates<br />
anywhere with<strong>in</strong> <strong>the</strong> network where communications are available.<br />
1 sec As <strong>for</strong> low-precision dynamic<br />
Real-time co-ord<strong>in</strong>ates are available<br />
As <strong>for</strong> low-precision dynamic<br />
Communications l<strong>in</strong>k between base <strong>and</strong> rover must be ma<strong>in</strong>ta<strong>in</strong>ed<br />
14 | GUIDELINES FOR THE USE OF <strong>GNSS</strong> IN LAND SURVEYING AND MAPPING
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