ISO 17123-9:2018

INTERNATIONAL ISO
STANDARD 17123-9
First edition
2018-12
Optics and optical instruments —
Field procedures for testing geodetic
and surveying instruments —
Part 9:
Terrestrial laser scanners
Optique et instruments d'optique — Méthodes d'essai sur site des
instruments géodésiques et d'observation —
Partie 9: Scanners laser terrestres
Reference number
©
ISO 2018
© ISO 2018
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ii © ISO 2018 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and subscripts . 2
4.1 Symbols . 2
4.2 Subscripts . 3
5 Requirements and recommendations. 3
6 Test principle . 4
6.1 General . 4
6.2 Procedure 1: Simplified test procedure . 4
6.3 Procedure 2: Full test procedure . 4
7 Simplified test procedure . 5
7.1 Configuration of the test field. 5
7.2 Example 1: Target scan by full dome scan . 7
7.3 Example 2: Two face target scan . 9
7.4 Measurements . 9
7.5 Calculation . 9
7.6 Derivation of a reference quantity for computing permitted deviations .12
7.6.1 Introduction .12
7.6.2 Determination of measurement uncertainty of the target centers .12
7.6.3 Derivation of the permitted deviation for the simple test procedure .13
7.7 Quantification of measurement deviations and judgement of the instrument for
the simple test procedure .13
7.7.1 Analysis of distance measurements .13
7.7.2 Remarks on the scale problem .14
7.7.3 Analysis of further distance differences .14
8 Full test procedure .16
8.1 Configuration of the test field.16
8.2 Measurements .17
8.3 Calculation .18
8.4 Statistical tests .21
8.4.1 General description .21
8.4.2 Question a) .22
8.4.3 Question b).22
8.5 Derivation of a reference quantity for computing permitted deviation .23
8.5.1 Determination of measurement uncertainty of the target centre .23
8.5.2 Derivation of the permitted deviation for the full test procedure .23
8.6 Quantification of measurement deviations and judgement of the instrument for
the full test procedure .24
Annex A (informative) Example for the simplified test procedure .26
Annex B (informative) Example for the full test procedure .28
Annex C (normative) Example for the calculation of an uncertainty budget of Type B .36
Bibliography .43
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see www .iso
.org/iso/foreword .html.
This document was prepared by Technical Committee ISO/TC 172, Optics and photonics, Subcommittee
SC 6, Geodetic and surveying instruments.
A list of all parts in the ISO 17123 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/members .html.
iv © ISO 2018 – All rights reserved

Introduction
This document specifies field procedures for adoption when determining and evaluating the uncertainty
of measurement results obtained by geodetic instruments and their ancillary equipment, when used in
building and surveying measuring tasks. Primarily, these tests are intended to be field verifications
of suitability of a particular instrument for the immediate task. They are not proposed as tests for
acceptance or performance evaluations that are more comprehensive in nature.
These field procedures have been developed specifically for in situ applications without the need for
special ancillary equipment and are purposely designed to minimize atmospheric influences.
The definition and concept of uncertainty as a quantitative attribute to the final result of measurement
was developed mainly in the last two decades, even though error analysis has already long been a part of
all measurement sciences. After several stages, the CIPM (Comité Internationale des Poids et Mesures)
referred the task of developing a detailed guide to ISO. Under the responsibility of the ISO Technical
Advisory Group on Metrology (TAG 4), and in conjunction with six worldwide metrology organizations,
a guidance document on the expression of measurement uncertainty was compiled with the objective
of providing rules for use within standardization, calibration, laboratory, accreditation and metrology
services. ISO/IEC Guide 98-3 was first published in 1995.
With the introduction of uncertainty in measurement in ISO 17123 (all parts), it is intended to finally
provide a uniform, quantitative expression of measurement uncertainty in geodetic metrology with the
aim of meeting the requirements of customers.
ISO 17123 (all parts) provides not only a means of evaluating the precision (experimental standard
deviation) of an instrument, but also a tool for defining an uncertainty budget, which allows for the
summation of all uncertainty components, whether they are random or systematic, to a representative
measure of accuracy, i.e. the combined standard uncertainty.
ISO 17123 (all parts) therefore provides, for defining for each instrument investigated by the procedures,
a proposal for additional, typical influence quantities, which can be expected during practical use. The
customer can estimate, for a specific application, the relevant standard uncertainty components in
order to derive and state the uncertainty of the measuring result.
INTERNATIONAL STANDARD ISO 17123-9:2018(E)
Optics and optical instruments — Field procedures for
testing geodetic and surveying instruments —
Part 9:
Terrestrial laser scanners
1 Scope
This document specifies field procedures for determining and evaluating the precision (repeatability)
of terrestrial laser scanners and their ancillary equipment when used in building, civil engineering and
surveying measurements. Primarily, these tests are intended to be field verifications of the suitability
of a particular instrument for the immediate task at hand, and to satisfy the requirements of other
standards. They are not proposed as tests for acceptance or performance evaluations that are more
comprehensive in nature.
This document can be thought of as one of the first steps in the process of evaluating the uncertainty of
measurements (more specifically of measurands).
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
ISO/IEC Guide 98-3, Uncertainty of measurement — Part 3: Guide to the expression of uncertainty in
me a s ur ement (GUM: 1995)
ISO/IEC Guide 99:2007, International vocabulary of metrology — Basic and general concepts and
associated terms (VIM)
ISO 3534-1, Statistics — Vocabulary and symbols — Part 1: General statistical terms and terms used in
probability
ISO 4463-1, Measurement methods for building — Setting-out and measurement — Part 1: Planning and
organization, measuring procedures, acceptance criteria
ISO 7077, Measuring methods for building — General principles and procedures for the verification of
dimensional compliance
ISO 7078, Building construction — Procedures for setting out, measurement and surveying — Vocabulary
and guidance notes
ISO 9849, Optics and optical instruments — Geodetic and surveying instruments — Vocabulary
ISO 17123-1, Optics and optical instruments — Field procedures for testing geodetic and surveying
instruments — Part 1: Theory
3 Terms and definitions
For the purpose of this document, the terms and definitions given in ISO 3534-1, ISO 4463-1, ISO 7077,
ISO 7078, ISO 9849, ISO 17123-1, ISO/IEC Guide 98-3 and ISO/IEC Guide 99 apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https: //www .iso .org/obp
— IEC Electropedia: available at http: //www .electropedia .org/
4 Symbols and subscripts
4.1 Symbols
Symbol Quantity Unit
c sensitivity coefficient —
d calculated distance m and mm
calculated mean distance m and mm
d
d measured distance m
obs
Δ distance difference m and mm
e eccentricity mm
F F-distribution —
I turning axis error °
k coverage factor —
k zero point error m and mm
z zero point error m and mm
ν degree of freedom —
2 2
Ω sum of squared residual m and mm
θ tilting angle °
φ turning angle °
r residual calculated by means of m and mm
single distances
residuals calculated by means of the m and mm
r
mean distances
S instrument station —
experimental standard deviation for m and mm
ˆ
s , s
a precision measure
experimental standard deviation for m and mm
ˆ
s
an accuracy measure
σ theoretical standard deviation of a m and mm
population
T target point —
u uncertainty various
U expanded uncertainty with cover- various
age factor k
x, y, z Cartesian coordinate m
χ Chi-Square distribution —
ζ Index error of tilting axis °
v
ζ resolution mm
2 © ISO 2018 – All rights reserved

4.2 Subscripts
Subscript Term
c collimation axis error
cen centring of targets
d calculated distance
calculated mean distance
d
Δ difference
diff diffusion of the measuring beam
ec eccentricity of the collimation axis
I turning axis error
ia incident angle
i,j index for target
ISO-TLS of standard uncertainty of the TLS (type A)
k zero point error
m maximum
ms manufacture specification
m0 scale factor
n index for station
φ turning angle
p typical influence quantities for the TLS measurements
pr pressure
pri primary rotation axis
r measured range
rc roughness
rh relative humidity
S instrument station
se sighting axis deviation
sec secondary rotation axis
sta stability setup
T target point
temp temperature
θ tilting angle
v0 tumbling deviation
w set number or repetition number
xyz 3D point
x,y,z cartesian coordinate
ζv index of tilting axis
ζθ resolution tilting angle
ζφ resolution turning angle
5 Requirements and recommendations
Before commencing the measurements, the operator shall ensure that the precision in use of the
measuring equipment is appropriate for the intended measuring task.
The laser scanner and its ancillary equipment shall be in known and acceptable states of permanent
adjustment according to the methods specified in the manufacturer’s handbook.
The coordinates are considered as observables because of modern laser scanners they are the standard
output quantities. All coordinates shall be measured on the same day. The instrument need not, but
may be levelled.
Meteorological data shall be recorded during the data acquisition in order to derive atmospheric
corrections. If possible the option for meteorological corrections within the software of the laser
scanner should be used. If the systematic deviations, created by the non-consideration of the
atmospheric corrections are too significant, and the automatic correction is not possible, then the raw
distances shall be corrected manually.
The operator should note the actual weather conditions at the time of measurement and the type of
surface on which the measurements are made. The conditions chosen for the tests should match those
expected when the intended measuring task is actually carried out (see ISO 7077 and ISO 7078).
Tests performed in laboratories would provide results which are almost unaffected by atmospheric
influences, but the costs for such tests are very high, and therefore they are not practicable for most
users. In addition, laboratory tests yield precisions much higher than those that can be obtained under
field conditions.
This document describes one field procedure with two different amounts of work as given in Clauses 7
and 8. If enough time is available, the full test procedure according to Clause 8 is recommended. It
allows a more refined and reliable judgement of the instrument.
6 Test principle
6.1 General
As raw observation values of laser scanners the x-, y- and z-coordinates of single points are treated. In
contradiction to other geodetic instruments, for example total stations, these coordinates do not have
a representative geometrical meaning. Furthermore, single points cannot be reproduced by repetition.
The quality of the scans can only be derived from estimated geometrical elements, like planes, spheres
or cylinders.
In the proposed test procedures the targets and the software for the target centre detection, which are
both important parts of the standard laser scanner equipment, shall be used as key elements for the
evaluation of the achievable precision. The 3D distances between the targets serve as indicator for the
quality of the measurements. The distances are chosen as datum independent measures for levelled
and non-levelled instruments.
Other targets, like spheres, may be used instead of the standard targets, which are recommended by
the manufacturer.
6.2 Procedure 1: Simplified test procedure
The simplified test procedure provides an estimate as to whether the precision of a given laser scanner
equipment is within the specified permitted deviation in accordance with ISO 4463-1.
The simplified test procedure is based on a limited number of measurements. This test procedure relies
on measurements of x-, y- and z-coordinates in a test field without nominal values.
An accurate standard deviation cannot be obtained. If a more precise assessment of the laser scanner
under field conditions is required, the more rigorous full test procedure as given in Clause 8, should
be used.
6.3 Procedure 2: Full test procedure
The full test procedure shall be adopted to determine the best achievable measure of precision
and partly accuracy of a laser scanner and its ancillary equipment under field conditions within
an acceptable time. The geometry of the test field is identical to the geometry of the simplified test
4 © ISO 2018 – All rights reserved

procedure. In this test procedure three series of measurements are taken instead of one series as in the
simplified test procedure. In addition, the statistical tests are applicable only for this test procedure.
7 Simplified test procedure
7.1 Configuration of the test field
In total two instrument positions and four target marks, also called targets, are arranged in a horizontal
and a vertical triangle. The measurement setup is shown in Figure 1 and Figure 2. Both triangles share
one edge. The two instrument stations S and S as well as the two targets T and T are aligned on the
1 2 1 2
shared edge. This is necessary in particular for the determination of a systematic distance deviation.
The dimensions of the triangles and also the distance between the two instrument stations are
determined essentially by the range of the examined TLS and by the maximum distance for capturing
the targets as recommended by the manufacturer.
The following recommendations concerning the measurement setup shall be taken into account:
— The two instrument stations S and S as well as the two targets T and T shall be aligned on a line
1 2 1 2
in space.
— Both the horizontal and the vertical triangle shall be realized as right-angled triangles (each with a
right angle at target T ).
— The hypotenuse S T of the horizontal triangle shall match the maximum recommended distance
1 3
for target capturing. This distance will be called maximum distance d in the following.
m
— The distance T T of the vertical triangle should be made as long as the local conditions permit
2 4
and it shall however be at least one third of the maximum distance. Moreover, the target T shall
be observed in steep sighting. The minimum value of 27° for the tilting angle, under which T shall
be observed from S , is recommended (see Figure 2). Table 1 gives some examples for possible
configuration of the test field.
— The desirable ratio of the cathetus in the vertical triangle is 1:1. If possible, a ratio of 2:1 shall not be
exceeded, however only in case the site allows for placing T sufficiently high.
Key
S , S instrument station
1 2
T , T , T , T target point
1 2 3 4
d maximum distance
m
Figure 1 — Configuration of the test field
Key
S , S instrument station
1 2
T , T , T , T target point
1 2 3 4
d maximum distance
m
Figure 2 — Vertical plane of the test field
6 © ISO 2018 – All rights reserved

Table 1 — Examples of distances for the testfield-setup based on the maximum distance d
m
Elev.
a b c d e
|S T | |S T | |S T | |S T | |S T | Angle on
1 3 2 1 1 4 2 3 2 4
S to T
1 4
m m m m m
°
20,00 6,67 19,44 11,06 10,00 30,964
25,00 8,33 22,19 17,00 12,50 34,287
30,00 10,00 25,00 22,36 15,00 36,870
35,00 11,67 27,85 27,49 17,50 38,928
40,00 13,33 30,73 32,49 20,00 40,601
45,00 15,00 33,63 37,42 22,50 41,987
50,00 16,67 36,55 42,30 25,00 43,152
a
d
m
b
1/3 d
m
2 2
c
TT ++()55m+ ST m
24 21
2 2
d
d −+55m+ ST m
()
m 21
e
1/2 d
m
— Several laser scanners deflect the laser beam by rotations about two orthogonal axes, one slowly
rotating axis (primary rotation axis) and one fast rotating axis (secondary rotating axis). This type
of laser scanners typically can scan the complete surrounding by turning only by 180° about the
slowly rotating axis, while the fast rotating axis deflects the laser beam to the front side (face I) as
well as to the back (face II) of the laser scanner. In order to detect systematic deviations (e.g. axis
misalignments) of the laser scanner and reliably check the instrument the following orientation
rule is required.
On station S as well as on S the face in which T is scanned shall be different from the face in
1 2 3
which T and T are scanned. This means, in case the targets are scanned in a full-dome scan, the
2 4
“seam line” of the full-dome scan always shall run between T and T /T . On instrument station S
3 2 4 2
the targets T , T and T shall be scanned in a different face than on S (see Figure 3 and Figure 4
2 3 4 1
dark grey hemisphere and bright grey hemisphere of the dome).
7.2 Example 1: Target scan by full dome scan
The targets will be scanned by a single full-dome scan on each station. On instrument station S the
TLS instrument is oriented in a way that the first vertical scan line will run between T and T /T .
3 2 4
The targets T , T and T will be scanned in face I and T will be scanned in face II. On position S the
1 2 4 3 2
instrument will again be oriented in a way that the first vertical scan line will run between T and T /
3 2
T , but now T and T are scanned in face II, while T and T are scanned in face I.
4 2 4 1 3
Key
A face I
B face II
S , S instrument station
1 2
T , T , T , T target point
1 2 3 4
Figure 3 — Instrument orientations on both positions (side view)
Key
A face I
B face II
S , S instrument station
1 2
T , T , T , T target point
1 2 3 4
Figure 4 — Instrument orientation on both positions (top view)
8 © ISO 2018 – All rights reserved

The seam line of the full-dome scan needs to run between T and T /T . The faces on both instrument
3 2 4
positions shall be inverted but can also be vice versa. Dark grey colour indicates the face I and the
bright grey one the face II.
7.3 Example 2: Two face target scan
The TLS instrument offers target scanning functionality in both faces. If all targets will be scanned in
both faces a selection process shall be carried out. When evaluating the measurements on instrument
station S for T , T and T the target scans in face I will be considered, while for T the target scan in
1 1 2 4 3
face II shall be considered. When evaluating the measurements on S it shall be vice versa: For T and
2 2
T the target scans in face II shall be considered, while for T and T the target scan in face I shall be
4 1 3
considered.
7.4 Measurements
Before beginning the measurements the instrument shall become acclimatised to the ambient
temperature (if not stated else by the manufacturer in the user manual, use 2 min/°C difference for
acclimatization). All coordinates shall be measured within a 24 hour period.
After completing the measurements, point clouds of the targets in form of three-dimensional Cartesian
coordinates are available, from which the centre coordinates, e.g. of spheres or chessboard targets shall
be determined. For this work step, the corresponding processing software of the manufacturer should
be used. It shall be ensured that irregular pixels are eliminated before determining the target centers.
After this work step, three-dimensional Cartesian coordinates for the centre points of the targets T
through T are available.
The four targets are scanned once from each station. The results are local 3D coordinates for each
target. Each station is defining a locale Cartesian coordinate system. The resulting coordinates are
listed in Table 2.
Table 2 — Coordinates of the local scans from S and S
1 2
Station Target
x y z
n,j n,j n,j
S T
n j
T x y z
1 1,1 1,1 1,1
T x y z
2 1,2 1,2 1,2
S
T x y z
3 1,3 1,3 1,3
T x y z
4 1,4 1,4 1,4
T x y z
1 2,1 2,1 2,1
T x y z
2 2,2 2,2 2,2
S
T x y z
3 2,3 2,3 2,3
T x y z
4 2,4 2,4 2,4
7.5 Calculation
The distances between the targets are calculated for instrument stations S and S according to
1 2
Formulae (1) and (2):
2 2 2
dx=−xx+− yz+−z (1)
() () ()
SS11,,ji ,,ijSS1 11,,ijSS11,,ijS
2 2 2
dx=−xy+− yz+−z (2)
() () ()
SS22,,ji ,,ijSS2 22,,ijSS22,,ijS
with i = 2, 3, 4 and j = 1, 2, 3
The resulting distances are summarized in Table 3.
10 © ISO 2018 – All rights reserved

Table 3 — Calculations for the distances between the targets
Distances for Station Distances for Station
S S
1 2
2 2 2 2 2 2
dx=−xy+− yz+−z dx=−xy+− yz+−z
() () () () () ()
SS11,,21,,21SS1 12,,SS11 12,,S11 SS21,,22,,22SS1 22,,SS21 22,,S21
2 2 2 2 2 2
dx=−xy+− yz+−z dx=−xy+− yz+−z
() () () () () ()
SS113,, 13,,SS11 13,,SS11 13,,S11 SS21,,32,,32SS1 23,,SS21 23,,S21
2 2 2 2 2 2
dx=−xy+− yz+−z dx=−xy+− yz+−z
() () () () () ()
SS11,,41,,41SS1 14,,SS11 14,,S11 SS21,,42,,42SS1 24,,SS21 24,,S21
2 2 2 2 2 2
dx=−xy+− yz+−z dx=−xy+− yz+−z
() () () () () ()
SS12,,31,,31 2 SS13,,12 SS13,,12 SS22,,32,,32SS2 23,,SS22 23,,S22
2 2 2 2 2 2
dx=−xy+− yz+−z dx=−xy+− yz+−z
() () () () () ()
SS12,,41,,41SS2 14,,SS12 14,,S12 SS22,,42,,42SS2 24,,SS22 24,,S22
2 2 2 2 2 2
dx=−xy+− yz+−z dx=−xy+− yz+−z
() () () () () ()
SS13,,41,,41SS3 14,,SS13 14,,S13 SS23,,42,,42SS3 24,,SS23 24,,S23

The distance differences Δ with i = 1, 2, 3 and j = 2, 3, 4 resulting from the two different scan positions
i,j
are calculated as follows:
Δ = d − d
1,2 S1,1,2 S2,1,2
Δ = d − d
1,3 S1,1,3 S2,1,3
Δ = d − d (3)
1,4 S1,1,4 S2,1,4
Δ = d − d
2,3 S1,2,3 S2,2,3
Δ = d − d
2,4 S1,2,4 S2,2,4
Δ = d − d
3,4 S1,3,4 S2,3,4
The values Δ , Δ , Δ , Δ , Δ , Δ are indicators for the geometrical quality of the scans. In the
1,2 1,3 1,4 2,3 2,4 3,4
ideal case they can be neglected. They should be within the specified permitted deviations ± U (see
Δ
also 7.6.2 for deriving the permitted deviations).
Δ is sensitive to a constant distance offset (i.e. zero point error) of the measured distances of the
1,2
laser scanner. For all other differences (Δ , Δ , Δ , Δ , Δ )deviations of the measured distances,
1,3 1,4 2,3 2,4 3,4
turning angles and tilting angles are superposing each other.
If the differences Δ are too large for the intended measurement task, it is necessary to continue further
i,j
in order to identify the main sources of the deviations. The presence of systematic measurement
deviations can be inferred from these differences if they differ significantly from zero. This evaluation
requires a quantitative assessment of the measurement uncertainty.
7.6 Derivation of a reference quantity for computing permitted deviations
7.6.1 Introduction
In this subclause, a reference quantity U for assessment of the distance differences calculated
Δ
in Formula (3) will be derived (see 7.6.2 and 7.6.3). The same derivation holds also for the full test
procedure and will be applied to calculate the permitted deviations (see 8.5 and 8.6).
7.6.2 Determination of measurement uncertainty of the target centers
To assess the significance of the distance differences from Formula (3), it is essential to make an
appropriate assumption regarding the standard uncertainty u , with which the target centers can be
T
determined by means of the laser scanner and the processing software. A simple option for determining
and fixing u in the simplified test procedure is the use of available manufacturer information.
T
However, to arrive at an approximation of the standard uncertainty u of the target centers which is best
T
representative for the true value, the greatest possible number of independent influence factors should
be incorporated into the uncertainty measure. One way of merging multiple independent influence
factors to a total uncertainty is offered by the ISO/IEC Guide 98-3:2008, Uncertainty of measurement —
Part 3: Guide to the expression of uncertainty (GUM, 2008), whose application is recommended also in
ISO 17123-1.
In the case of an uncertainty quantity u for the target centers, for instance the following quantities can
T
be used:
— Uncertainty measure by statistical analysis of series of observations (Type A): An uncertainty
measure for the target centre precision can be derived by means of an empirical standard deviation
of repeated target scans.
12 © ISO 2018 – All rights reserved

— The manufacturer specifications (Type B): The data sheets of some manufacturer can contain a
3D accuracy for capturing the recommended target marks, which can be incorporated as an
uncertainty quantity of Type B directly into an uncertainty measure u for the target centers.
T
Alternatively, the 3D accuracy of the target capture can be derived from the specifications of the
angle and distance accuracies in case both the number of points used for measuring the targets
and the modelling accuracy regarding the target centers are additionally taken into account. Some
manufacturers provide both systematic measurement deviations and a measurement noise as a
function of distance and reflectivity. These specifications can also be included.
— Values stemming from one's own experience (Type B): Influence factors that are known from one's
own experience to affect the uncertainty of the target centers may be taken into account as well.
The derivation of a combined measurement uncertainty is demonstrated in general in ISO 17123-1, and
ISO 17123-5 for the example of total station measurements. Annexes B and C also give examples.
7.6.3 Derivation of the permitted deviation for the simple test procedure
In case the uncertainty quantity u for the target centers is available, the reference value u for assessing
T Δ
the distance differences determined in Formula (3) shall be derived. Given u , first the uncertainty u of
T d
the computed distances is obtained with the uncertainty propagation law as
uu=× 2 (4)
d T
Using u , the uncertainty u of the distance differences
d Δ
uu=× 22= u (5)
Δ d T
can be computed by applying the uncertainty propagation law again. The expanded measurement
uncertainty
U = k · u (6)
Δ Δ
indicates an area containing a majority of the measurements that appear to be probable
measurement values.
NOTE A frequent choice is k = 2, which corresponds in case of a correctly assumed normal distribution to a
confidence interval of 95 %.
The expanded measurement uncertainty U with k = 2 for distance differences results in
Δ
U = k · u = k × 2 × u = 4 u (7)
Δ Δ T T
The uncertainty U shall be used in the following as the reference quantity for assessing and judging
Δ
the distance differences.
7.7 Quantification of measurement deviations and judgement of the instrument for the
simple test procedure
7.7.1 Analysis of distance measurements
To detect a constant distance offset, the distance between T and T is analysed. This distance is not
1 2
influenced by a constant distance offset when the measurements of instrument station S are used,
whereas the influence of a constant distance offset is doubled when the measurements of station S
are used, see Figure 1 and Figure 2. Forming the difference Δ given in Formula (3) in analogy to the
1,2
”Partially Distance Method” yields twice the value of a constant distance offset. The value Δ shall be
1,2
compared with the expanded measurement uncertainty U from Formula (7). In case of
Δ
|Δ | > U (8)
1,2 Δ
a significant systematic deviation of the distance measurement is assumed. In this case, an adjustment
by the manufacturer or, if the TLS permits, the input and storage of the determined deviation as a
correction value in the device followed by a control measurement is recommended. It shall be avoided
to consider further deviations Δ since they are superimposed by the influence of the systematic
i,j
deviation of the distance measurement. In case of
|Δ | ≤ U (9)
1,2 Δ
no significant systematic deviation of the distance measurement can be ascertained, and it is then
reasonable to analyse the influence of systematic deviations in the further distance differences.
[1]
NOTE For more information concerning the distance deviation see Deumlich and Staiger .
7.7.2 Remarks on the scale problem
It should be remarked that the described testing configuration does not allow for an analysis of the
instrument's scale since this would require reference values for the target distances. In case these
reference values are known, e.g. from independent measurements with superior accuracy, the
instrument's scale can be determined. Measurement uncertainties such as centering deviations or
insufficient consideration of the meteorological conditions shall be avoided by all means, because
otherwise they are misinterpreted as a scale correction. For instance, a centering deviation of 1 mm
causes, on an 80 m long distance, a value of 12,5 ppm for a supposed scale correction. Therefore, it is
more advisable to determine the instrument's scale by means of a fixed test bay, in which the reference
distances were determined from tacheometric network measurements.
[2]
NOTE For more information concerning the scale problem by TLS see Feldmann as well as Staiger and
[5]
Heister
7.7.3 Analysis of further distance differences
Concerning the analysis of direction and angle measurements, it should be pointed out first that
deviations in the axis system from its reference geometry (deviations of the sighting and tilting axes)
have an influence on the direction of the turning circle that depends on the steepness of the sighting.
[4] [1]
NOTE See Stahlberg as well as Deumlich and Staiger .
To detect deviations, it is therefore indispensable to include the high target T in the following
investigations. For this reason, all distance combinations between targets T , T , T and T are
1 2 3 4
calculated. Using Formula (3), the differences for these distances are: Δ , Δ , Δ , Δ , and Δ .
1,3 1,4 2,3 2,4 3,4
The reason for considering all distance differences is that, depending on the magnitude and the sign of a
systematic deviation both in the direction of the turning circle and in the tilting angle, the effects show
up either in horizontal plane and/or in vertical plane. The computed differences shall be compared with
the expanded measurement uncertainty from Formula (7). In case of
|Δ | > U or |Δ | > U or |Δ | > U or |Δ | > U or |Δ | > U (10)
1,3 Δ 1,4 Δ 2,3 Δ 2,4 Δ 3,4 Δ
other significant systematic deviations of the instrument are assumed. Before making this final
decision, different error sources should be identified and eliminated, e.g.:
— The targets are stable and set up on solid ground.
— The instrument was set up on a stable tripod on solid ground.
14 © ISO 2018 – All rights reserved

— Instrument had been acclimatised to the ambient temperature before the measurements were
started.
— The used equipment is in good condition (tripods, tribrachs, adapters).
— Check measurements for gross errors.
In case no error source can be identified and the significant deviation is confirmed, it shall be assumed
that there is a significant systematic deviation either of the direction angle of the turning circle or of
the tilting angle, or that there are deviations of all sources. In such a case, the execution of the full
test procure is recommended. If the full test procedure cannot be carried out, then the simplified test
procedure shall be repeated with a slightly different configuration of the test field, e.g. by changing the
locations of the instrument stations slightly. If this test also fails, an adjustment by the manufacturer is
recommended.
With the presented testing procedure, it is not possible for the user to determine and take into account
the individual effects, because effects, e.g. of axis deviations, interfere with each other or partly
compensate each other. It should be remarked that the instrument's deviations lead indeed to systematic
deviations of the three-dimensional coordinates of the considered points. This fact, however, cannot be
exploited to carry out a more differentiated examination of the individual deviations since the analyses
are based on distances in space, and thus on relative quantities.
A schematic overview of the TLS testing procedure presented here is given in Figure 5 in form of a
flow chart diagram. Annex A provides an example intended to use the simple test procedure described
throughout Clause 7.
Figure 5 — Flow chart diagram of the TLS simple test procedure
8 Full test procedure
8.1 Configuration of the test field
The test field is identical to the test field for the simplified procedure, see Figure 1 to Figure 4. The size
of the test field can be modified depending on the capabilities of the scanner and the actual size of the
object for which the scanner will be used.
16 © ISO 2018 – All rights reserved

8.2 Measurements
Before commencing the measurements, the instruments shall be adjusted as specified by the
manufacturer. Furthermore, the instrument shall become acclimatized to the ambient temperature (if
not stated by the manufacturer in the user manual, use 2 min/°C). All coordinates shall be measured
within a 24 h period (see 7.4).
Three series of measurements (w = 1, 2, 3) are carried out on each instrument station, which means
that each of the four targets is scanned three times from each instrument station. The sequence is as
follows: All targets are scanned three times from the first station S . Once the first instrument station
is completed, the same procedure will
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