Transcript GNSS Validation - Australian Institute of Mine Surveyors

GNSS Verification
AIMS Mudgee Seminar
February 2008
Derrin Lee
Registered Mining Surveyor
Xstrata Glendell Mine
Disclaimer:
The purpose of this presentation is to
raise awareness of this issue and to foster
debate.
This topic is considered by many as a
“Grey Area”.
Each surveyor should arrive at their
own conclusions as to what is necessary in
order for them to comply with applicable
regulations.
What are GNSS?
GLOBAL
NAVIGATIONAL
SATELLITE
SYSTEMS
(Cl 5 Surveying Regulation 2006)
What are GNSS?
Most surveyors are familiar with the Global
Positioning System (GPS).
GNSS is relatively new terminology.
It describes not only GPS, but the whole
range of emerging satellite positioning
technologies.
These technologies include:
The European Commission's GALILEO,
Russia's GLONASS & China’s COMPASS.
GPS turned 30 yesterday, 22nd February 2008.
The first GPS Satellite (SVN01) was
launched from Vandenberg Air Force Base
California on 22nd February 1978.
Who currently uses GNSS?
How many people here today use GNSS?
Which methods do you use:
•
Real Time Kinematic (RTK)
Post Processed Single Baselines (Static or Fast
Static)
•
Post Processed Multi Baseline (e.g. AUSPOS Online
Processing)
•
Network base solutions (e.g. VRS or CORS such as
SydNET)
•
Limitations of GNSS
GNSS observations are currently NOT traceable to
a recognised value standard.
All GNSS are operated by INTERNATIONAL
parties.
These ARE NOT under the surveyor’s direct
control.
As such, any GNSS equipment and techniques
used must be validated.
Verification or Calibration?
Unlike EDM equipment, GNSS receivers
cannot be calibrated for scale.
Verification IS NOT Calibration
Calibrate:– Adjust, attune, standardise.
Verify:– Confirm, authenticate, corroborate,
make sure.
Why verify your GNSS?
Why do you verify your EDM?

As a professional surveyor it is in your interest not
to use any measuring equipment unless you
know the accuracy obtained by its use.

The “Survey And Drafting Directions For Mine
Surveyors 2007 (NSW – COAL)” require surveys
to be carried out to a standard.

To provide Legal Traceability
What the Mining Regulations say:
S+DD For Mine Surveyors 2007(NSW – COAL)
3.3.1 Accuracy: Each control survey and subsidiary
survey must be planned and surveyed to ensure
these surveys satisfy the conditions to achieve a
standard of accuracy as prescribed in ICSM, SP1 to
achieve Class D or better.
3.3.3 Secondary surveys shall be employed by the Mining
Surveyor where necessary to accurately locate all of
the Mine workings on the Mine Workings Plan to
within 1mm at 1:2000 Scale. (i.e. 2m) Such surveys
shall be completed to the highest appropriate
standards of accuracy.
S+DD For Mine Surveyors 2007(NSW – COAL)
3.5.1 Order of accuracy of benchmarks:
Such levelling shall be completed to ICSM SP1 Class
“LD” or Class “B” standards of accuracy.
3.5.2 Accuracy of Mine workings:
Such levelling shall be completed to ICSM SP1 Class
LE standard of accuracy or to within 0.1 metre.
STANDARDS AND PRACTISES FOR CONTROL SURVEYS
ICSM SP1
(Version 1.6)
Part B 2.6 Global Positioning System
2.6.4
If required, the equipment and software can
be validated over existing, high quality
geodetic network marks.
SURVEY AND DRAFTING DIRECTIONS FOR
MINING SURVEYORS
Issued as an adjunct to General Rule 2000 under the Mines
Inspection Act 1901
3.11 Maintenance and Adjustment of Survey
Equipment
3.11.1 Survey equipment used for baseline or
other precise surveys should be maintained
regularly and kept in good adjustment.
3.11.3 GPS equipment should be verified against
an approved control network upon acquisition
and after any change in software, firmware
or hardware.
What the Land Surveying
Regulations say:
Surveying Regulation 2006 (NSW)
Cl 3 Application of Regulation
This Regulation applies to all land surveys, and to
all surveys referred to in section 4 or 5 of the Act,
but does not apply to any mining surveys
except to the extent to which the other provisions
of this Regulation expressly provide and to the
extent provided by an order in force under clause
4.
Surveying Regulation 2006 (NSW)
Cl 4 Mining surveys
(1) The Surveyor-General may, by order published in the Gazette, give
directions with respect to the conduct of mining surveys.
(2) Such an order may only be made on the recommendation of the Board.
(3) The document entitled Survey and Drafting Directions for Mine
Surveyors, published in March 2000 by the Department of Mineral
Resources, is taken to be an order under this clause with respect to
mining surveys carried out for the purposes of the Coal Mines Regulation
Act 1982 and the Coal Mine Health and Safety Act 2002, and may be
amended and repealed accordingly.
(4) The document entitled Survey and Drafting Directions for Mining
Surveyors, published in December 2001 by the Department of Mineral
Resources, is taken to be an order under this clause with respect to
mining surveys carried out for the purposes of the Mines Inspection Act
1901 and the Mine Health and Safety Act 2004, and may be amended and
repealed accordingly.
Surveying Regulation 2006 (NSW)
Cl 14 Equipment for measurement of surveys
(5) A surveyor must not use any GNSS equipment
in making a survey unless it is verified against
the State control survey:
(a) at least once every year, and
(b) immediately after any service or repair, and
(c) immediately after any change or upgrade of
software.
(6) The accuracy and method of any verification
under this clause must be as approved.
Surveyor General’s Directions
No. 9 - GPS Surveys
Currently under review
A draft document has been prepared as:
Surveyor General’s Directions No. 9
GNSS for Cadastral Surveys
Draft Direction No.9
In light of the non prescriptive mining
regulations:
I believe that the Draft Surveyor General’s
Direction No. 9 provides the best indication of
the current thinking on using GNSS for legal
purposes.
Draft Direction No.9
This draft has been prepared by:
Simon McElroy
Senior Surveyor (Geodesy and CORS)
Survey Infrastructure and Geodesy
Land and Property Information
NSW Department of Lands
These are Simon’s thoughts.
They are not official.
Draft Direction No.9
Legal traceability of GNSS measurements is
an extremely complex issue.

At the present time it is unresolved at a State,
Federal & International level.

In the interim surveyors are strongly
encouraged to connect to marks in the NSW
State Survey Control network that have legal
traceability.

Draft Direction No.9
Responsibility of the surveyor to ensure that
their GNSS equipment and techniques will
achieve a result in terms of the accuracy
required.
 The most appropriate way to maintain
accuracy is by connection to the State Survey
Control Network.
 This will validate the surveys reliability, scale
and orientation.

Draft Direction No.9
Surveyors are strongly encouraged to connect
to marks in the NSW State Survey Control
network that have legal traceability; these
include:
Established marks
 Accurate AHD marks

(as per the Surveying Regulation 2006)
Draft Direction No.9
Surveyors should not be deterred from using
GNSS for legal purposes provided that they:
Adopt GNSS best practice guidelines.
 Confirm at least one GNSS observation
against established marks for each survey.
 Validate their GNSS techniques annually
against higher order marks in the State Survey
Control Network.

Draft Direction No.9
Survey Confirmation (Each Survey)
A basic two dimensional “relative” check only.
 At least one independent GNSS observation
confirmed against an external source.
 Confirmation is achieved if the measurement satisfies
the accuracies required by the Surveying Regulation
2006.
 The above obviously applies to cadastral surveying. A
suitable substitution for mine surveying might be:
Measurement satisfies the accuracies required by the
Survey and Drafting Directions.

Draft Direction No.9
Annual Validation
A rigorous 3D “absolute” validation.
 Conducted annually for each GNSS equipment or
technique used. Techniques must be the same as
typically used by the surveyor.
 Minimum of 4 Marks. Hz Order 2 or better. Vrt Order
L3 or better. Latest coordinates obtained from SCIMS.
 Values of one station held fixed. Coordinates of other
stations determined by GNSS technique.

Draft Direction No.9
Annual Validation
Non fixed station
Non fixed station
Non fixed station
Fixed station
Draft Direction No.9
Annual Validation
Difference between derived coordinates and SCIMS
used to determine if validation is acceptable.


Validation acceptable if difference is:
<25mm + 5ppm Hz and < 60mm+ 12ppm Vrt.
ppm is calculated on the distance between the non
fixed stations.

Draft Direction No.9
Annual Validation
The validation should be repeated if changes/upgrades
are made to:
GNSS Receivers (Hardware or Firmware)
 Techniques used
 Processing Software

Draft Direction No.9
State GNSS Test Networks
The Surveyor General has established two precise
GNSS networks. Bass Hill and Newcastle University.
 These may be used for annual validations.
 Precise 3D coordinates are available for all marks.
(They may differ slightly from SCIMS).
 Detailed instructions are available from the
Department of Lands.

A Hypothetical Scenario
Open cut coal mine.
 Survey Method: RTK GNSS (GPS + GLONASS)
 GNSS Base fixed at survey office.
 A “Site Calibration” is used for day to day
RTK surveying.

What could the surveyor do to verify their
equipment?
Firstly: Is a “Site Calibration” a
verification of my equipment?




NO
Using a “Site Calibration” results in a correction
being applied to each RTK measurement.
The correction is calculated as a best fit to the
control stations used in defining the “Site
Calibration”.
(If the “Site Calibration” is used as part of
everyday surveying it should be used when
verifying the survey technique.)
Annual Validation




Identify at least 4 Marks in SCIMS with at least
Order 2 Hz and Order L3 in the vicinity.
Select marks that surround the workings. Where
possible include the Mine Baseline terminals.
Survey the marks using the same techniques
typically used. Don’t forget you are validating
your software and hardware. Consider the geoid
model.
With the GNSS Base fixed determine the
coordinates of the 4 marks.
Annual Validation

Determine the difference between the
surveyed coordinates and SCIMS
coordinates.

The validation could be seen as
acceptable if the difference is:
<25mm + 5ppm Hz
and
< 60mm+ 12ppm Vrt.
Survey Confirmation




Each survey:- At least one independent GNSS
observation confirmed against an external
source is required.
Make a measurement to a mark of the required
order in SCIMS.
If there is no convenient mark in SCIMS
consider placing and surveying your own mark
to the required order.
Refer to the S+DD for the required accuracy of
the confirmation. It will depend on the
requirements of the survey.
Best Practise Guidelines
I would recommend that all surveyors using
RTK techniques read:
SP1 Part B 2.6.8.4
Observational Requirements for RTK GPS
Techniques
References
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
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
S+DD For Mine Surveyors 2007(NSW – COAL)
STANDARDS AND PRACTISES FOR CONTROL SURVEYS
ICSM SP1 (Version 1.6)
SURVEY AND DRAFTING DIRECTIONS FOR MINING SURVEYORS
Issued as an adjunct to General Rule 2000 under the Mines
Inspection Act 1901
Surveying Regulation 2006 (NSW)
Surveyor General’s Directions
No. 9 - GPS Surveys
Links
http://www.lands.nsw.gov.au/about_us/publications/guidelines/surve
yor_generals_directions
http://www.insidegnss.com/about
Questions
The End
Use of RTK GNSS
Techniques to survey
Mine Workings
A RTK survey, as carried out in most open cut
coal mines to locate mine workings, is in effect
a series of radiations from a single fixed
GNSS base station.
This can be equated with an underground
mine surveyor who utilises a total station to
measures distances and directions from a
control station to determine the location of
underground mine workings.
The RTK radiations used to survey
workings are not “Control or Subsidiary
Surveys”. The best way to classify them
is as “Secondary Surveys”.
S+DD 2. Definitions
Secondary Surveys: A survey based on
Control Surveys or Subsidiary Surveys utilised
by the Mining Surveyor to accurately locate all
of the workings of the Mine that are not
included in Control Surveys or Subsidiary
Surveys.
S+DD 3.3.3
Secondary Surveys shall be employed by the
Mining Surveyor where necessary to
accurately locate all of the Mine workings on
the Mine Workings Plan to within 1mm at
1:2000 Scale. Such surveys shall be
completed to the highest appropriate
standards of accuracy.
So 3.3.3 informs us that Secondary
Surveys are allowed, and that the
required accuracy of the surveyed mine
workings is 2m (i.e. 1mm at 1:2000).
What about heights?
S+DD 3.5.2
Accuracy of Mine workings: Such
levelling shall be completed to ICSM
SP1 Class LE standard of accuracy or
to within 0.1m.
So provided that the GNSS base station location
is derived from a Control Survey or Subsidiary
Survey (i.e. Surveyed to Class D Horizontal and
Class LD or B Vertically) and Mine Workings are
located to with 2m horizontally and 0.1m vertically
then the surveyor is in compliance with the S+DD.
There is no explicit requirement of the S+DD to
verify the accuracy of the GNSS equipment when
used for a Secondary Survey.
It might be considered good practice to survey a
check radiation to a known point before and after
surveying Mine Workings.
This is analagous with an underground surveyor
who, when set over a control mark with a total
station, takes a backsight and then confirms their
orientation by checking to another control station.
For Control and Subsidiary surveys the S+DD
requirement to verify the accuracy of GNSS
equipment is implied through the requirement to
comply with SP1.
If RTK techniques are used to perform “Control
Surveys” then they must comply with the
requirements of SP1 in order to achieve results of
Class D. (S+DD 3.3.1)
To comply with SP1, new stations are
recommended to be re-occupied from a minimum
of two base stations.
It is desirable for some new stations to be reoccupied from a third base station.
It is also necessary to conduct an analysis to
determine the class of survey actually achieved.