Exercise: Tacheometer, GPS, Network...

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01.04.2010Prof. Dr. H. Ingensand Geodetic Metrology and Engineering Geodesy

Exercise:Tacheometer, GPS, Network

Adjustment

Engineering Geodesy II

Goals of the Exercise

• Densification of a TPS and GPS network• Data flow of TPS and GPS• Using TCRP1201, in particular sets of angles measurement• Static measurements using GPS-System 500 and 1200• Post-processing of GPS-Data• Data flow of TPS- and GPS into LTOP• Combined network adjustment using LTOP, study of scenarios• Visualisation of network plots

Engineering Geodesy II – Prof. Dr. H. Ingensand2

• Place: HIL-Attica (see pillar network plan)

• New coordinate determination of four pillars

• Determination of four new points (marked on the ground)

• Methods: TPS and GPS

• Combined adjustment in LTOP

• Study of scenarios

Timing

• Thu, 19.03.2010: TPS measurements

• Thu, 26.03.2010: GPS measurements

• Thu, 01.04.2010: Adjustment, Analysis

Measurement: Sets of Angles

• Today, for cadastral- and land surveying no significance

• Engineering Geodesy: basic networks (e.g. tunnel-portal networks, deformation networks)

• Prior to measurement: quick recognisance of targets and verification that observations are possible

• Measurements should be carried out uninterrupted and quick

• First telescope position clockwise, second telescope position anti-clockwise, → pillar rotation!

• Usage of sunshade to protect instrument

Leica Program “Sets of Angles”

• TPS 1200 – application (costs!…)

• Options to obtain results in various formats

• Format manager: Tool of Leica Geo Office

• Format mask LTOP_Satz_Me.frt (geomETH)

• Correction of meteorology in the field (only for instrument station, assuming identical meteorology at target)

• Take attention to instructions (in particular the notes in SETUP)

TPS Measurements

TPS Measurements 19.03.2009

• Angle measurements at pillars and points on the ground → each group sets up at one pillar and one point marked with a screw

• Try to measure as many pillars as possible

• Pillars on the roof: arrangements between groups in respect of pillar occupation

• Allocation of instrument stations to the groups: see first page in the exercise instructions

Don‘t do

1. Die Stehachse muss senkrecht auf die Libellenachse stehen.

2. Die Kippachse muss senkrecht auf die Stehachse oder parallel auf die Libellenachse stehen.

3. Die Zielachse muss senkrecht auf die Kippachse stehen.

4. Die Stehachse Kippachse und Zielachse müssen sich in einem Punkt schneiden (Fernrohrmittelpunkt

5. Die Stehachse muss durch den Mittelpunkt des Horizontalkreises gehen.

6. Die Kippachse muss durch den Mittelpunkt des Vertikalkreises gehen.

7. Die Nullrichtung des Vertikalkreises hat bei exakter Horizontierung in den Zenit zu weisen.

Sind diese Bedingungen nicht erfüllt treten Fehler in der Winkelmessung auf!

Don‘t do

Ein Vermessungspfeiler ist die stabilste Vermarkung für einen Vermessungspunkt.

Sie werden vor allem für Messpunkteerrichtet, auf denen wiederholte Beobachtungen erforderlich sind – z. B. bei Deformations- und Kontrollmessungen an Staumauern oder anderen technischen Großprojekten.

Don‘t do

Comparison Accuracy of GPS - TPS Surveying

According to F. Brunner, TU Graz

GPS-Measurements 26.03.2009

• Measurements using 2 Leica GNSS SmartAntenna and 6 Leica GNSS 1200 or Leica GPS 500

• 2 static sessions à 20-30 minutes (begin and end in agreement)

• Simultaneous measurements at four pillars and four ground points on the HIL Attica

• Exchange of receivers and antennas between both sessions

• Config Set: PP_Static• Antenna: AX 1202 GG / AT 502 (Tripod or Pillar), check on antenna• Pillar: h = 0.208 but measure height, tripod: measure height with special

scale.• Update: e.g. 5 sec (agree to one)

16 Engineering Geodesy II – Prof. Dr. H. Ingensand

Application of GNSS in Engineering Geodesy

• Basic networks & local construction site networks:– Roads, railroad lines, channels– Tunnels, bridges, industrial sites– Airports, harbours, etc...

• Deformation measurements (at different epochs or continuous): – Land slides, rock falls, tectonic movements– Dams, bridges, etc.

• Accuracy range:– 1 mm to 1 cm depending on the application

Future GNSS Availability

MEO: Medium Earth Orbit 2’000 – 35’786 km

GEO: Geostationary Orbit 35’786 km

Future GNSS Availability

GPS/GLONASS/Galileo combined with 15° masking angle

GPS+GLONASS 25.3.2010 08.00-11.00

Benefits of Multiple Satellite Systems

- improvement of continuity (unlikely of errors occurring simultaneously)

- improvement of accuracy (less bad PDOPs)

- less multipath problems

- less time to solve ambiguities

- improvement of availability (urban canyons, trees, indoors)

- improvement of reliability (jamming, outliers)

number of satellites

Precise Ephemeris

• Broadcast Ephemeris (from satellite): accuracy in dm-range

• Precise Ephemeris: accuracy in cm-range

• „a posteriori“ determined values (with a delay of 17 hours / 12 days)– Access via internet: e.g. NASA

http://igscb.jpl.nasa.gov/components/prods_cb.html– SP3 - format (directly importable into Leica Geo Office, internet-download)– CODE (Centre of Orbit Determination for Europe): Astronomic Institute of

Uni Bern, GNSS Service: satellite orbits & station coordinates formatted for Bernese GPS Software

• Precise Ephemeris are only useful for huge distances (> 40 km)

• Reflexion at planes (walls, floor, rocks)

• Superposition of direct and indirect signals

• Best case: no solution• worse case: false solution!• in particular for short sessions (<30

min.) or equal satellite constellations (e.g. successive days)

• careful point selection, not next to walls

• measure at different times• long station occupation• Choke-Ring-antennas (not cheap!)

Multipath (Mehrwegausbreitung)

• mechanical and electronic centres are not identical

• depends on the constellation

• magnitude: 1 - 3 mm

• use of same antennas and same orientation guarantees same value

• two antennas should have same orientation (e.g. cable connection towards south, use compass)

Antenna Phase Centre

carrier frequency, C/A- und P-Code characteristics

achievable resolutionL1: 1575.42

L2: 1227.60 MHz

L3: nuclear detonation detection

L4: additional ionospheric correction

L5: Safety of Live Use (first launch in 2009)

CA-Code (Coarse Acquisition, Repetition every millisecond)

(Precise, weekly repetition)

Source Effect

Signal Arrival C/A ± 3 m

Signal Arrival P(Y) ± 0.3 m

Ionosphericeffects ± 5 m

Ephemeris errors ± 2.5 m

Satellite clock errors ± 2 m

Multipath distortion ± 1 m

Tropospheric effects ± 0.5 m

GPS – Surveying Strategies

Static• occupation of all stations static• use of a proper reference point• occupation time 30 min to 1 day• accuracy 5 mm + 1 ppm• for smaller networks 1 mm is

achievable

Rapid-Static• quick static method• use of one reference point• occupation time is a couple

minutes for each point• accuracy 5 -10 mm + 1 ppm

Kinematic• determine antenna while in motion

AROF: ambiguity resolution on the fly

• no static initialisation

Real Time• radio link to reference• initialisation couple seconds• loss of satellite not problematic• efficient method• no post processing necessary• 10 mm + 1 ppm

Static: Sessions

• example: 4 receivers, 6 points, 3 sessions

• each point 2 occupations good interconnection

• good accuracy with limited number of receivers

• complicated logistics

Rapid Static

Reference• open horizon• protected• power supply!• SWIPOS, AGNES Webserver →

RINEX observation data

Rover• each point is occupied twice: at

different time of day, receivers• occupation time: 5 minutes (in

case of bad GDOP 10 to 15 minutes)

Advantages:• efficient, 2 receivers suffice,

simple planning

Datum transformation between to reference frames

Projection 1

Ellipsoid 1

L, B, h

Cartesian

X, Y, Z

Projection 2

Ellipsoid 2

L, B, h

Cartesian

X, Y, Z

7 - Parameter - Transformation

3 Translations, 3 Rotations, 1 Scale

Differences between CH 1903 and WGS84

differences in latitude CH1903 minus WGS84 in arc seconds

WGS84 → Swiss Grid CH1903

Swiss coordinate system: • map projection: oblique (schiefachsige) Mercator on an 1841 Bessel ellipsoid• geodetic datum: CH1903 (fundamental point Berne 600’000 m E, 200’000 m N)

Relation between WGS84- and Bessel ellipsoid is unknown!• relation between ellipsoid-centres is unknown• relative orientation between both systems is unknown

Approximate relation via transformation of known points• GRANIT: measurements of LFP1-points using GPS 1986 / 1987 (not to be used)• adjustments of 7 parameters

Simple transformation: 3 translations• fitting using reference points

GPS-Heights → Orthometric Heights

h = H + N• h = ellipsoidal height• H = orthometric height• N = geoid undulation

How to get N?• from a mass model• program CHgeo2004

Geoid of Switzerland in 1 by 1 km grid– bi-quadratic interpolation– http://www.swisstopo.ch

• add geoid undulations → approximate grid coordinates / orthometric heights

Das Geoid der Schweiz (CHGeo2004) relativ zum lokalen Referenzellipsoid

WGS84 → Swiss Grid

• transformation to reference points– LTOP - adjustment, ev. in combination with tachymetric measurements:

constrained or stochastic transformation (stochastische Lagerung)– Helmert - Transformation (Leica Geo Office, TRANSINT, VERATOP)

How obtain approximation values for unknowns?

from the map e.g. Swisstopo: http://www.swisstopogeodata.ch/geodatenviewer/

Alternatives to obtain approximation values

Optimisation function is usually convex if inconsistencies are small- Adjustment without any approximation values: Use of a global optimisation

algorithm, even if objective function is multimodal- Determine manually approximation values from observations- Some software (e.g. Cramer Caplan) has a function to determine

approximative values

LTOP – next steps

• Add all mes-files to a single file• Add approximate values of unknowns to koo-file• Run LTOP – free adjustment (use “Neupunktseditor” F – N)

LTOP: from a free to a constrained network

Why use a free (= minimum constraints) network?• detection of gross errors• quantification of inner accuracy of a network

Free tachymeter network:• two points fixed in horizontal positions, one unknown scale• one point is fixed in height

Options for a Geodetic Datum

• Constrained network– inner accuracy is influenced– constrains between datum points are not separable from measurement

errors

• Stochastic datum (= Anschlusspunkte als Beobachtung)– reference points are introduced with appropriate accuracies– coordinates of reference points will change– Cuation: for official land surveying purposes (amtliche Vermessung) the

reference points can not be changed (LFP2)

LTOP – graphical presentation of results

Free network (magnification factor of errors 10 000)

LTOP – graphical presentation of results

t = textread('uebfreemitscale.prn','%[^\n]');

line_nr = strmatch('KOO', char(t));

LTOP – GPS

GPS – Coordinate Sets in LTOP

• Separate adjustment of horizontal and height components

• new set of coordinates for each session minimum 3 translations for each session

• e.g. 3 translations, optionally 1 rotation (around vertical axis) and 1 scale

• transformation parameters are considered as unknowns and determined by adjustment

• Keep only significant parameters. Do not use scale as a parameter, if scale = 0.2 ppm (KORR) +- 0.3 ppm (MF)

…what we expect

- One LTOP adjustment of the combined network (*.dat, *.mes, *.koo *.prn)

- Some brief comments via e-mail until Thursday, 15.4.2010

- A lengthy report is not necessary: short comment on the results

- suggestions on improvement

Exercise: Tacheometer, GPS, Network...

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