cadastral principles tci workshop 17 october 2007 grenville barnes
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Cadastral Principles
TCI Workshop17 October 2007
Grenville Barnes
Content• Purpose
• Cadastral vs Geodetic points
• Cadastral System
• Boundary Types
• Cadastral Surveying Process
• Cadastral Evidence
• Heterogeneity Example
• Professional Trends
PURPOSE OF CADASTRAL SURVEYING
• Demarcate and Identify Boundaries
• Collect Evidence to Perpetuate Boundary Location to Promote Security of Tenure
• Obtain Data to Represent Boundaries in an Abstract Form (graphical and mathematic evidence)
Where is the parcel?
What size (area) is the parcel?
What are the dimensions of the parcel boundaries?
What constitutes the parcel boundaries?
What is the unique identifier of the parcel
Specific Purpose of a Cadastral System
Multipurpose Land Information System
Geodetic Infrastructure
CadastralDatabase
SurveyRecords
• natural resources• infrastructure• socio-economic
RegistryInformation
Owners/LesseesSource of rights
RestrictionsEncumbrances
Parcel Identifier
Information Layers
Spatial Geo-reference
Framework
Cadastral Survey
Cadastre
INFRASTRUCTURE MEASUREMENT MANAGEMENT
Components of a Cadastral System
The spatial geo-reference framework provides a common reference system for the integration of tenure and other land information.
Cadastral vs Geodetic Points
Location of geodetic points is a question of mathematics (coords may vary if datum changes or through readjustment)
Location of cadastral points (parcel corners) is defined by law and evidence (location depends on interpretation of cadastral evidence, especially physical evidence
Cadastral surveying is the process of defining and describing boundary evidence
Fixed vs General Boundaries
• Fixed - corners/bendpoints are beaconed and boundary is the invisible line in between the beacons
• General – a physical feature (hedge, wall, fence, etc.) is accepted as the boundary and mapped
Point Typology
• Parcel corner beacons
• Indicatory beacons
• Control stations (e.g. traverse) – connection to geodetic network
• Geodetic Control Points
Cadastral Surveying Process
• Prior to fieldwork acquire cadastral data on previous surveys of the parcel and adjoining parcels (Reg. 10)
• Search for original beacons in field • Survey in found monuments and permanently demarcate
control stations (link to geodetic control)• Compare found evidence with previous survey evidence
(measurements, beacons, etc)• Recompute and Replace missing beacons• Document survey (report, coord list, comps, fieldbook,
etc)
How does this change with use of GPS technology??
Cadastral Surveying Challenge
Cadastral boundaries are surveyed by different surveyors at different times to different specifications using different equipment…..
As a result they are a heterogeneous set of points
Can GPS promote homogeneity?
Cadastral Data as Evidence
Mathematical/Measurement
Physical
Graphical
beacons
fencesimprovementswitness marks
distancesangles
coordinatesarea
Index mapSurvey plan
Verbal
Hierarchy of Cadastral Evidence
Field Notes/ Observations
REALITY
Physical Parcel beacons
Computations
Measurements
Coordinates
Survey Plan
Index MapINCREASING
ABSTRACTION
Area Calculation
Beacon description
Incr
ea
sin
g w
eig
ht
of
ev
ide
nce
2
(200)
(150)(150)
(200)
ORIGINAL (PARENT) PARCEL
(Assume that coordinates are fixed in database)
BA
CD
26
27
28
(150’)
(200’)
(200’)
(150’)Rem of 2
147’
198’
Owner of 2 requests three 50’x100’ parcels be subdivided out of parent parcel
A
C
B
D
26
27
28Rem of 2
(200)
49’(150)
(200)
49’
49’
(150)
99’
99’
99’
Surveyor finds A, B and C and several other original beacons and proves thatthese are original, undisturbed and consistent
What happens to the ‘fixed’ coordinates in the database???
Measurements are never exact – they contain systematic and random errors
C
BA
D
FUNDAMENTAL PRINCIPLES
• Equipment is calibrated prior to first use and periodically after that (e.g. 6 monthly)
• Measurement to property corners are checked with independent measurements
• The original survey provides a definitive description of the parcel boundaries
• Relocation of parcel boundaries is determined by a consideration of various evidence
Open Thick bush
Low L
and
V
alue
Terrain/Access
Cadastral Record EvidenceGood Poor
Cad
astr
al
Fie
ld
Evi
den
ce
High
Good
Poor
Most Expensive
More expensive
Least Expensive
Matrix of Rural Survey Cost Components
Surveying Professional Trends
• Develop ‘thin’ Survey/Mapping Department that deals primarily with Quality Control and Project Management
• Contract out surveys to private sector
• Government responsible for geodetic infrastructure
• Emergence of surveying profession (private and public)
Cadastre 2014 – FIG 20 year Vision • Show the complete legal situation of land, including public rights and restrictions.• Separation between ‘maps’ and ‘registers’ will be abolished.• Cadastral mapping will be defunct; it will be replaced by modeling.• “Paper & pencil cadastre” will be replaced by modern technology.• Cadastre will be highly privatized with public and private sector working closely together.• Procedures for definition of private and public land objects will be identical.
http://www.fig.net/cadastre2014/
Reg. 36 (2)(c)
“A surveyor shall not use a loop traverse closing on his starting point if it is practicable to traverse between two previously fixed stations.”
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