Managing a Cadastral SDI Framework Built from Boundary Data

Managing a Cadastral SDI Framework Built from Boundary Data • Michael Elfick • Tim Hodson • Curt Wilkinson

Agenda • Introduction – Current situation • Background and Design Concepts • Data Model • Workflow

The influence of GPS • GPS enabled systems will be everywhere • To make GPS truly valuable, GIS must supply underlying mapping information • This information must be accurate • Accurate data greatly extends the usefulness of GIS

Typical errors in digitized data

Goal A simple system to create and manage spatially accurate cadastral geometry in a GIS. The system must be extendable and: Follow survey methods Be able to improve existing datasets Maintain spatial relationships between the Cadastre and associated GIS layers.

Scope of Technology • Focus on cadastral geometry • not a full cadastral system • A key part of a GIS system • Designed to be an extendable platform • For land records and cadastre • Complements a civil and survey system

Cadastral Fabric • The fabric is a continuous surface of connected parcels • It is also a dimensioned boundary network • Has an explicit topology, defined by common parcel corners and neighbors • Topology is inherent in the model, and is defined and enforced during data entry

Survey Measurements • In the past, measures of bearing and distance were much easier than fixing a location on the surface of the earth • Land surveys are parcel dimensions, with known error in the measures • Parcels are also defined by their relation to other parcels • So, measures and connections were known, but true coordinates were not

From Measures to Coordinates • We need accurate coordinates for the fabric and associated GIS layers • Accurate coordinates are close to the true coordinates • Implies there is a real object (not always) • and we know how close (statistic of error) • For Instance, Control Points have: • A physical location (monument) • Error information (level of confidence)

Central Concepts • Often, associated GIS layers are created and maintained in context with the Cadastre • An accurate Cadastre can serve as the ‘control’ for the rest of the GIS • If we capture the shifts in coordinates of the Cadastre, we can then adjust the associated layers and maintain spatial relationships • The result is more accurate coordinates all around

Edited only by Cadastral Editor Editable by standard GIS ESR Shapes Coordinates Measurements Derived from Coordinates Computed from LSA – held by Points From Survey or Records – held by the Line Central Design Concept • Differentiation of Source information from derived information

Fabric Fundamentals • Parcels are the ‘unit of work’ • Create & edit parcels • Join parcels to the fabric • Control points ‘fix’ the fabric • Connected (and historic) parcels have redundancyof measurements • Multiple measurements & control points processed in a least squares adjustment

Parcel Parcel Model • Parcels are represented by : • parcel linefeatures, • parcel pointfeatures, and • parcel polygonfeatures, • referred to in aggregate as parcel features

Parcel Model • Parcels are defined by non-spatial data, and • Parcels have spatial data – dimensions on lines

Model of a Parcel • Lines have geometry defined by dimensions and by points

Points & Control Points • A control point is an special type of parcel point, giving that point an enhanced status

Plans • Plans are used to represent a collection of information about a legal land document

Data Model Plans - Concepts • Most Parcels are associated with a planandJobs are often based on Plans • Plans and all associated parcels can be recovered from the Cadastral Fabric • Plans hold the metadata for parcels (go back to legal document of origin) • You can extend the Plan concept to fit your organization, for example: • you can add to the schema for other sorts of metadata about the document

Plans Model Status manages the life-cycle of the Plan

4 4 4 2 7 1 6 2 3 6 2000 1985 1994 History - Concepts • Parcels updated with new record information are never deleted from the Fabric, they are simply marked as Historic • 4 different types of historic information maintained: • State of the Cadastre on a particular date • State of the Fabric on a particular date • Lineage of a Parcel • History of Adjustments to the Cadastral Fabric

Workflow Customisation • This can start with adding new attributes (fields) to the Cadastral Fabric Tables • The Cadastral Editor can be used to edit these attributes via the Property Inspector • The Cadastral Editor UI is written using ArcObjects components, overlying an editing engine

Workflow System Integration • Cadastral fabric tables can have relationships to other geodatabase tables via relationship classes • So other systems, like a text based title management database, can be linked to the cadastral geometry of the fabric

Workflow Editing Workflow

Workflow Jobs – “Work-Orders” • A Job is a “work-order” for creating, modifying or adjusting one or more parcels. For instance: • Entering a parcel subdivision • Entering control points • Adjustment • Jobs can be saved, or committed • Jobs can be open for any length of time

Data Model Locked Parcels • A job may lock parcels, no other job can edit the parcel attributes or dimensions • Parcel Points are never locked • This allows LSA adjustment while jobs are open • If not locked, standard reconcile will detect conflicts

Workflow Parcel Editing • The ‘unit of work’ • Parcels are created by entering a loop traverse of the parcel boundary • Parcel closurereport is a first level Q/A check First Level QA check

Workflow Parcel Join - Concepts • Parcel Joining enforces the topologicalmodel relationships between parcels • Join is an interactive ‘point and click’ UI • Match shared points • Automatic scale and rotate • Auto-join utility • Second level QA check provided by the transformation residuals during a join

Parcel Join Second Level QA check

Join • Joining is the easiest and fastest way to build the Fabric • Join process ensures fit to the Fabric • No slivers possible • No accidental overlaps • Automatically handles translation, scale, rotation from local reference system • Each newly joined parcel adds valuable information that can be used in future least squares adjustment jobs

Least Squares Adjustment • Fabric + Control +LSA = Good Coordinates • Preparation of the data is half the work • The fabric model and the software does this • LSA does more than improve the coordinates • Shows where control is needed • Finds errors in the data (eg. incorrectly entered measurements…) • Extensive Reports on analysis of the data • Works only on the coordinates, never changes the original measurement values

Workflow Job Adjustment • Once the Control has been tested, job adjustment is easy • Set tolerances • Select constraints • Straight lines • Line points

Workflow Job Commit (close-out) • Before a change is inserted into the Cadastral Fabric the system does integrity checks : • Tests of bounding parcel coordinates • Notify if need to readjust • If parcels were not locked, then reconcile • On commit, the system: • Calculates adjustment vectors • Updates job, history… • Releases locks on the parcels

Workflow Associated Feature Classes • On commit, the transaction manager creates a set of Adjustment Vectors • Each point’s coordinate residual provides a vector that may be used on the GIS layers • Vector sets are stored as a history of coordinate shifts based on each least sq. adjustment • GIS Layers can be updated using the Adjustment Vectors • You decide when to make a GIS layer update to the Cadastral Fabric • This is possible because Cadastral Fabric maintains the adjustment “history” of each layer

Workflow GIS Layers Adjustment

SUMMARY • ArcGIS has been extended for cadastre data • Improve existing data, regardless of quality • It uses survey methods • Can follow a job workflow, and keep history • Applies cadastral adjustments to feature classes • Is an easily extended and customized system • It supports ‘remote’ editing • It supports pessimistic locking • Can be scaled to very large datasets

Managing a Cadastral SDI Framework Built from Boundary Data