Related Manuals for Leica Geosystems GPS System 500
Summary of Contents for Leica Geosystems GPS System 500
- Page 2 Congratulations on your purchase of a new System GPS500 from Leica Geosystems.
- Page 3 Introduction Overall planning for a GPS survey Mission planning Observation times and baseline lengths Field observations Importing the data to SKI-Pro Deriving initial WGS 84 coordinates for one point Data-processing parameters Baseline selection - Strategy for computation Interpreting the baseline results Inspecting the logfile and comparing results Storing the results Adjustment, Transformation and output of results...
- Page 4 Introduction ........... 6 Importing the data to SKI-Pro ....22 Checking and editing during data transfer ....22 Backing up raw data and projects ......22 Overall planning for a GPS survey ....7 Baseline length ............7 Deriving initial WGS 84 coordinates for Temporary reference stations for Rapid Static surveys .
- Page 5 Interpreting the baseline results ....32 Adjustment, Transformation and output of results ............39 Baselines up to the limitation value......33 Ambiguities resolved ............33 Ambiguities not resolved ..........34 Notes on single-frequency static and rapid Baselines above the limitation value ......34 static measurements........
- Page 6 Surveying with GPS has become Although this guide has been written popular due to the advantages of specifically for Leica Geosystems accuracy, speed, versatility and GPS - System 500 and System 300, economy. The techniques employed much of the information is of a...
- Page 7 A GPS receiver measures the Rapid Static surveys feature short incoming phase of the satellite observation times. It is particularly signals to millimeter precision. important for Rapid Static that However, as the satellite signals ionospheric disturbances are more or propagate through space to earth less identical for both sites.
- Page 8 As observation time and accuracy In terms of productivity and accuracy, are mainly a function of baseline it is much more advantageous to length, it is highly recommended that measure short baselines (e.g. 5km) baseline lengths should be kept to a from several temporary reference minimum.
- Page 9 In all types of survey work it is sound Depending on the accuracy required, A partial check can be obtained by practice to cross check using inde- the user should be prepared to check using two reference stations instead pendent measurements. In classical newly surveyed points.
- Page 10 For baselines up to about 20 km, one Generally speaking, the longer the When you inspect the satellite will usually attempt to resolve the baseline the longer one has to summary and GDOP plots, you will ambiguities using the Rapid Static observe.
- Page 11 System 500 and System 300 provide The common points should be accurate relative positions of points spread evenly throughout the project that are observed in a GPS network area. For a correct computation of all and linked in post-processing. The transformation parameters (shifts, coordinates are based on the WGS rotations, scale), at least three - but...
- Page 12 Overall Planning Temporary Reference Stations In terms of productivity and accuracy, it is usually Plan the campaign carefully preferable to measure short baselines from several Consider the job, number of points, accuracy needed temporary reference stations rather than trying to measure long baselines from just one central point.
- Page 13 The GDOP value helps you to judge For successful, high-accuracy GPS Poor windows should only be used to the geometry of the satellite surveying it is advisable to take the bridge between two or more good constellation. A low GDOP indicates observations in good windows.
- Page 14 Selecting Good Windows Example: Window for Rapid Static: 4 or more satellites above 15° cut-off angle. GDOP ≤ 8. Whenever possible: 5 or more satellites. GDOP ≤ 5. Satellites above 20°. Always: Good window - GDOP low and stable Poor window - GDOP high Use sky plot to check for obstructions.
- Page 15 The observation time required for an Unless one is extremely restrictive, it is impossible to quote observation times accurate result in post-processing that can be fully guaranteed. The following table provides a guide. It is based depends on several factors: baseline on tests in mid-latitudes under the current levels of ionospheric disturbance length, number of satellites, satellite with a dual frequency Sensor.
- Page 16 Times and Baseline Lengths Observation time depends upon: • Baseline length • Number of satellites • Satellite geometry (GDOP) • Ionosphere Ionospheric disturbance varies with time, day/night, month, year, position on earth's surface. The table provides an approximate guide to baseline lengths and observation times for mid latitudes under the current levels of ionospheric activity when using a dual frequency Sensor.
- Page 17 The results for all roving points will Note that the reference GPS surveying is a differential depend on the performance of the receiver does not have to be technique with baselines being reference receiver! Thus the set up on a known point. It is "observed"...
- Page 18 The computation of a baseline in If WGS 84 coordinates for one site When computing the Single Point data processing requires that the are not known or cannot be derived, Position for the starting point of a coordinates of one point (reference) the Single Point Position computation network, always compute for a site are held fixed.
- Page 19 The operator of the roving receiver The Stop and Go Indicator on the As the Stop and Go Indicator can should also pay attention to certain sensor provides the roving-receiver only monitor the roving receiver it can points. This is particularly important operator with an approximate guide only provide an estimate for the for Rapid Static surveys with short...
- Page 20 As with all survey work, it is well worthwhile filling out a field sheet for each site when taking GPS observations. Field sheets facilitate checking and editing at the data- processing stage. Reference Stations Roving Receiver 15° cut-off angle. No obstructions above 15° cut-off angle. Obstructions should not block signals.
- Page 21 Practical Hints Field Sheet Tribrachs: check the bubble and optical plummet. Point Id.: Date: Level and center the tribrach and tripod correctly. Receiver Serial No.: Operator: Check the height reading and antenna offset. Memory card No.: An error in height affects the entire solution! Type of set up: Use a radio to maintain contact between reference and Height reading:...
- Page 22 Data can be transferred to SKI-Pro Note that some of the above After reading in a data set always directly via a PC-card slot, or via a site-related parameters can make a back-up on either a diskette card reader, from the controller be changed in some or on the hard disk.
- Page 23 As explained on page 18, the As explained on page 17, the See section "Need for one known point in WGS 84" on page 18 for computation of a baseline requires reference receiver does not have to that the coordinates of one point are be on a known point.
- Page 24 In the vast majority of cases, the It is common practice in GPS It can sometimes be advantageous, default settings for data-processing surveying to set a 15° cut-off angle in however, to increase the cut-off angle may be accepted and may never be the receiver.
- Page 25 If code measurements are corrupted SKI-Pro uses the broadcast For precise GPS surveying, one will for some reason, one can process ephemeris recorded in the receiver. normally accept the system default baselines using "Phase only" . setting "Automatic" , which will usually This is standard practice throughout the world for all routine GPS use Code and Phase observations.
- Page 26 For baselines above this limitation With this parameter you can The Rms threshold is used to value, a so-called L3 solution is determine how SKI-Pro should minimize the possibility of unreliable performed. The L3 observable is a compute baselines. The system baseline results.
- Page 27 For longer observation times - let us The following table provides a very approximate guide to the rms of a say about 30 minutes or more - the single difference that a user could expect: rms threshold can be set higher without undue risk.
- Page 28 The advantage of using this model is The solution type parameter applies This parameter is only used for that it is calculated according to to all baseline up to which baselines up to the limitation value conditions prevalent at the time and (see page 26, "Fix ambiguity up to"...
- Page 29 It will not make much difference to Using this option may support SKI-Pro will automatically select to the end result as to whether you ambiguity resolution on medium and process whatever data is available. select the Hopfield or Saastamoinen longer lines when you suspect the Thus there is little point in processing model, but you should never work ionosphere to be quite active.
- Page 30 Before starting data processing one It is highly advisable to check the Try to avoid mixing baselines of should consider carefully how best to coordinates for each temporary- totally different lengths in the same compute the network. Points to be reference station using double fixes computation run.
- Page 31 Data Import and Computation Consider the following carefully: • How best to compute the network Check and edit during data transfer: • The need for good WGS 84 coordinates for one point Point identification • Connection to existing control Height reading and antenna offset •...
- Page 32 When interpreting the results, one For baselines above the limitation has to distinguish between baselines value, a so-called L3 solution (linear up to the limitation value ( "Fix combination of L1 and L2 ambiguities up to" ) and baselines measurements) is performed. This above this value (see page 26).
- Page 33 These will usually be the "true If the guidelines for baseline lengths, values". observation windows, number of For baselines up to 20 km (system satellites, GDOP, and observation default for "Fix ambiguities up to" ), However, one should also be aware times are followed (combined ambiguity resolution should always that very severe ionospheric...
- Page 34 As already explained, ambiguity Note that for baselines up For baselines above the limitation resolution should always be to 20 km it should normally value (system default = 20 km), SKI- successful for baselines up to 20 km be possible to resolve the Pro eliminates the ionospheric effects if good results are to be obtained.
- Page 35 For baselines up to the limitation As explained in section "Rms The reason is that this could allow value, ambiguity resolution using the threshold" (see page 26), if the rms unreasonably high rms float and fix Lambda search and the FARA float exceeds the rms threshold, the values and could therefore lead to a statistics is always attempted.
- Page 36 For baselines above the limitation If the results are not as good as you If a point was observed twice in value (system default = 20 km), SKI- would expect, it can be well different windows or two reference Pro eliminates the ionospheric effects worthwhile comparing the information receivers were operating but does not attempt to resolve...
- Page 37 It follows that you should exercise a After inspecting the summary of certain amount of care when storing results and the logfile, store the points that have been fixed in more results that meet your accuracy than one baseline computation. requirements.
- Page 38 Interpreting and Storing the Results • For lines up to 20 km, ambiguity resolution should be • Baselines above the limitation value successful if high-accuracy results are to be obtained. (default = 20 km): L3 solution, ambiguity resolution not attempted. •...
- Page 39 After the observations have been computed, you may wish to adjust the results if multiple observations to points exist. This provides the best estimates for the position of the points. See SKI-Pro online help "Adjustment" for further details. The results of the baseline computations are coordinates in the WGS 84 system.
- Page 40 When measuring with the SR510 Recommended (minimum) A Rapid Static observation can (System 500) or SR9400 / SR261 observation times: usually be considered to be (System 300) there are several successful when SKI-Pro can resolve points that should be noted in order the ambiguities.
- Page 41 If the highest possible accuracy should be achieved it is recommended to orient the antennas in a common direction. On long baselines above 10 km the accuracy which can be achieved with single frequency Sensors is inferior to that which can be achieved with dual frequency Sensors due to ionospheric effects which cannot be eliminated with single frequency data.
- Page 42 712168-2.0.0en Printed in Switzerland - Copyright Leica Geosystems AG, Heerbrugg, Switzerland 2000 Original text...
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