Presentation on theme: "Water Corporation take on Referential Topology WALIS Referential Topology Workshop April 09 Presenter: David Bulfield."— Presentation transcript:
Water Corporation take on Referential Topology WALIS Referential Topology Workshop April 09 Presenter: David Bulfield
2 Cadastral Re-alignment Project What is the Cadastral Re-alignment Proposal ? – It is a misnomer for an asset re-alignment exercise to shift the locations of some 3+million asset records to a new set of cadastral boundaries across the State. Land base is maintained independently by Water Corporation based on proposed subdivision & Development activity Asset information is plotted in relation to proposed or actual parcel edges and road casements.
3 What is different with a Utility We deal almost exclusively with linear and point objects Generally, objects are related to but not necessarily linked (snapped) to boundary offsets. Every spatial shift of a parcel edge corner results in shift vectors applying to every “related” object. Changing lengths of linear objects can’t always be reconciled. And we still have to contend with polygon slivers from static boundary layers (eg; Loc Govt, MRS etc..)
5 Conflict in Our Business Needs Submit Development Application to DPI DPI Refers to Agencies for comment Applicant submits proposed asset details for approval Engineering/p recalc survey revisions Deposit Plan at Landgate WAPC Final Approval Data captured into GIS – continually revised & updated from Survey information Landgate capture data from lodged survey plans. Current lodged survey plans applicable until this point
6 The Cadastral relativity problem Data was originally digitised from hardcopy plans at various scales with a resulting low degree of spatial accuracy. ~1992, the Water Corporation stopped utilising spatial updates from the authoritative Landgate database and maintained data in isolation. Landgate continued to improve accuracy of its SCDB. Adhoc acquisitions of data from Landgate in outlying urban areas revealed a growing disparity with Core Land data. Recent expansion (explosion) of digital data requests and experienced GIS users indicates customers may not be as willing to “warp” our data to fit theirs.
7 Examples of current data variation Figure 1 Example of variation of road centreline to parcel edges. - Boyanup Road centreline - Green Parcel edges - Black Figure 2 Example of parcel edge variation Landgate to Water Corporation. - Boyanup Landgate - Blue Water Corporation - Black
8 Another example Road centre-line Our street location
9 Issues with Boundary Offset Relationships 2.5m offset from corner Note change in pipe length !
10 So, What’s the point? If we never share our data – keep it to ourselves, then we don’t need to do anything. Why not just ignore the impact on others and our own data capture issues and continue as before. Why not just delete all the land and start again. Someone else has done this before – why not ask them why they did it (& how)?
11 Our Project - Progress to date Phase 1 - Feasibility completed – Identified a significant impact on the business when comparing our asset locations against other external datasets. – Identified at least 17 prospective toolsets ostensibly covering the land base alignment process. Phase 2 - toolset evaluation pilot, cost and revised process discovery just started.
12 Other takeaways! Regardless of the known, accurate absolute location of our assets, we are obliged to relate asset location to cadastre. Use of Imagery greatly increases the perception of land base error. There is a product discrepancy between source data and user’s required accuracies. Dependent customer agencies should not be subjected to unnecessary “shifts”.