GPS BASED PHASESHIFT ROBOTIC TOTAL STATION TARGET TRACKING SYSTEM

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GPS BASED PHASE-SHIFT ROBOTIC TOTAL STATION
TARGET TRACKING SYSTEM Elton Chen
Combine hand-held computer with portable GPS
receiver for robotic total station tracking
The goals of this research project is to study
the feasibility of using a low cost GPS system
to provide an efficient target tracking mechanism
to assist the RTS survey measurement by (1)
deriving a set of simple mathematical models to
allow the coordinate interchange between local
coordinate (RTS regular grid system) and the
geodetic coordinate systems (used by GPS) and
(2) to study how the adjacent environment
(buildings, vegetation, moving object) may have
affected the performance of the tracking. The
results indicated that the tracking efficiency
and accuracy depend on (1) levels of multi-path
and GPS signal strength imposed by adjacent
environment, (2) the initial walking pattern of
the prism pole (with CF-GPS attached) and number
of GPS points being acquired and averaged, (3)
distance between the total station and the GPS.
The preliminary analysis also showed promising
results using a low cost GPS receiver to assist
automatic target tracking in various challenging
operating environment.
Collect and analyze GPS positioning data, GPS
assisted total station tracking performance
GPS positioning quality data
Compute GPS data distribution pattern defined by
ratio Sx/Sy
Select four sites represent different challenging
operating environment

• Open sky reference benchmark points with direct
  line of sight to the GPS satellites (all ref-xx
  points)
• Woody area under different canopy conditions
  (various crown closure). Site labeled as W1,W2,
  W3
• Street segment with constant traffic
  interference. Site labeled as T1
• Area around the concrete building where
  multi-path occurs. Site labeled as B1

W1
W2
W3
Total station search tracking performance
Model derivation (warp the earth surface)
define a common reference system to allow the
coordinate interchange between local coordinate
(RTS regular grid system) and the geodetic
coordinate systems (used by GPS)
B1
T1
Schedule Conduct field data collection
N is local northing you are solving for. E
is local easting you are solving for. Y is
intermediate mapping plane north coordinate,
calculated from the measured LLH on the map
projection. X is intermediate mapping plane
east coordinate, calculated from the measured LLH
on the map projection. K Scale Factor is the
scale applied from the intermediate mapping plane
to the local plane. T Rotation Angle is the
rotation angle from the intermediate mapping
plane to the local plane. TY Translation
Northing is the shift in Y axis from the
intermediate mapping plane to the local
plane. TX Translation Easting is the shift in
X axis from the intermediate mapping plane to the
local plane. YO Origin Northing is the
coordinate on the intermediate mapping about
which the rotation and scale are applied. XO
Origin Easting is the coordinate on the
intermediate mapping plane about which the
rotation and scale are applied. (Note k, ?, TY,
TX , YO, and XO are the six parameters of the
calibration 2D similarity transformation)
Tracking time decreases as the distance from
prism pole to total station increases (search
angle decreases-means it takes less time to
complete the search
Prepare equipment material
Summary conclusions

• Trimble S6 Robotic Total Station with Tripod and
  Prism Pole
• TDS Recon Windows CE handheld computer
• Holux compact flash GPS and Garmin handheld eTrek
  GPS
• Digital stop watch
• Safety vest and safety cone for survey
• Equipment moving cart
• Wooden stakes

• System performs very well under all operating
  environment with an average tracking time of 2-5
  seconds (except under tree canopy conditions)
• System performance improves as the distance from
  GPS prism pole to total station increases (due to
  the decrease in search angle)
• GPS data distribution pattern (defined by the
  ratio between standard deviation of GPS
  positions Easting and standard deviation of GPS
  positions Northing) plays very important role.
  The preliminary result shows the distribution
  pattern seems to out-weigh the dilution of GPS
  position precision and accuracy caused by
  multi-path from adjacent objects
• Uniform distributed GPS data improves the
  performance of the tracking system (see Figure to
  the right)

BIBLIOGRAPHY
Curve showing system performance time to lock
on to the prism increases as the ratio between
the standard deviation of GPS positions Easting
and the standard deviation of Northing,

• Brinker, R. C., and Minnick, R. (Eds.). (1995).
  The Surveying Handbook (2nd Ed.). New York
  Chapman Hall.
• Bugayevskiy, L. M., and Snyder, John P. (1995).
  Map Projections A Reference Manual. New York
  Taylor Francis.
• Topcon Positioning Systems Inc. (2005). Topcon
  RC2 engineering specification document,
  Livermore, CA.
• Leica Geosystems. (2003). Leica TPS design
  specification. St. Gallen, Switzerland.
• Nichols, Mark (2000). GPS-aided autolock in a
  robotic total station system. US Patent No.
  6035254.
• Smith, James (1997). Introduction to Geodesy
  The History and Concepts of Modern Geodesy. New
  York John Wiley and Sons, Inc..
• Van Sickle, Jan (2001). GPS for Land Surveyors
  (2nd ed.). New York Taylor and Francis.
• Van Sickle, Jan (1995). Construction Surveying
  and Layout. Indiana Creative Construction
  Publishing.
• Wolf, Paul R. and Ghilani, C. D. (2002).
  Elementary Surveying An Introduction to
  Geomatics (10th Ed.). New Jersey Prentice Hall.
• Yang, Q., Snyder, J. P., and Tobler, W. R.
  (2000). Map Projection transformation
  Principles and Applications. London Taylor
  Francis.

• Future works should address
• Over simplification of mathematical
  transformation of projection and datum
• Additional treatment to eliminate the effect from
  atmospheric and Ionosphere conditions
• Better quantify the site conditions effect on
  the GPS signal multi-path
• Auto-correlation between GPS measurement of
  Northing and Easting
• Minimize the effect of the Satellite
  constellation (by conducting experiment using a
  satellite mission planning approach