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The Shape and Tab File Work Flow in SAM Lite
Now everyone can move to newer more accurate Digital Cadastres.

SAM Lite implements all aspects of upgrading spatially dependant layers such as utilities, assets, annotation layers to a new digital cadastre.

Even Zoning layers can be upgraded but may need topology snapping after the upgrade process to accommodate the differing number of vertices between the two digital cadastres.

The following is an overview of the work flow implemented in the SAM functionality.

Many GIS Professionals are familiar with the necessary processes of ‘checking’ spatial data out of the master themes, editing the data, and ‘checking’ the spatial data back in. Each GIS vendor has various processes in place to assist their customers achieve this.

There are (at least) four distinct processes in this Work Flow.
Process 1 Checking the data out of the ‘Master Themes’. This includes marking the data in the Master Themes as being ‘Checked Out’ thus preventing edits/deletes by other users and processes. Typically the data is written somewhere temporarily for the duration of the work, and for the sake of convenience this is called a ‘Temporary Work Area’ in this article.
Process 2

Process 2/ Copying the data from the ‘Temporary Work Area’ into some environment where the changes are to take place.
Process 3 Process 3/ Saving the changes back into the ‘Temporary Work Area’.
Process 4 Checking the data back into the Master Themes from the ‘Temporary Work Area’, which often comes with numerous spatial, aspatial and temporal data integrity rules to be complied with.

If one deals with ‘flat’ file structures such as ESRI Shape files and MapInfo Tab files one can bypass much of the complexities of dealing with databases, record locking, and the interplay between spatial features and related attribute data dealing with the assets and parcels, ownership, tenure, connectivity, currency, and so on.
  Indeed, with ‘flat’ file structures such as ESRI Shape files and MapInfo Tab files:
  1. Locking the ‘Database’ as such is handled by the operating system.
  2. Marking Spatial Features that have been checked out is a human memory function.
  3. Rolling back the database is as simple as retrieving one’s backup.
  4. Projections can be handled consistently by adopting the ‘Proj4’ Projection Engine.
  5. There are tools in the public domain to deal with Shape and Tab Files.
Indeed, when dealing with spatial data held in object or relational databases, there can be many legacy issues getting data into the database. What can often happen is that a database is initially populated with the spatial and aspatial data available at the time. As time goes on there can be many database triggers and validation rules imposed into the ‘check-in’ process. Naturally the data already loaded is not subject to these rules, the logic being that as time goes on the various parcels, assets, etc will be checked out, edited, and fully proofed before it is checked back in. This leans on the notion of ongoing improvements as time and resources are available.

The problem has been that one has to checkout a lot of utility, asset, annotation, zoning and other layers that are spatially dependant on the digital cadastre in order to move it to its new position relative to an improved digital cadastre.

There are often issues with the amount of time that features are checked out. Many Utilities have obligations on their GIS units to incorporate new assets and incorporate updates in short time frames, thus checking out an area for a week for editing purposes may cause may break “Key Indicators”????

For these reasons (and others???) it is much easier to develop an ‘End to End’ work flow for upgrading spatial data to a new digital cadastre.

This article explains the process as implemented by the Spatial Adjustment Manager (SAM) available from Spatial Tapestry.

There are several scenarios in the spatial upgrade field. These are:

  1. Digital Cadastral Upgrade from Survey and Title Dimensions.
  2. Digital Cadastral Upgrade from Occupations observed from Orthophotgraphy.
  3. Upgrading Spatially Dependant Layers with a replacement Digital Cadastre.
  4. Upgrading Spatially Dependant Layers in a partially upgraded Digital Cadastre.
And each requires a different work flow. This article discusses “Upgrading Spatially Dependant Layers with a replacement Digital Cadastre”, which seems to be a common occurrence as many GIS departments have had great difficulty dealing with the upgrade issue for may years.

First, the concept of a “Temporary Work Area” (TWA) has to be covered. A TWA needs to be big enough to have some significance in the scheme of things, but not so large that the data processing time encroaches unreasonably on the use of the master themes.

Since SAM can process 3 to 4 square kilometres an hour using the “Iterative Best Guess” algorithm and 1 square kilometres per 3-4 hours using the “Least Squares Adjustment” algorithm, one can pick a running size for the TWA’s.

A TWA boundary can in itself cause a range of problems, depending on the circumstances present in the GIS IT Environment. E.g. if a TWA Boundary goes through an area of large shifts it is likely that some points in some features will cross over into an adjoining TWA polygon. When this happens features that cross the TWA boundary can be seriously distorted until the adjoining TWA is also upgraded. Further there is the issue of tracking these points and preventing them being moved a second time, which is fortunately existing functionality in SAM.
This Icon is used to select a TWA. The user simply uses this tool to click anywhere inside the TWA to be upgraded next.

This Icon is used to extract the spatial features from the various themes that are “Inside and Crossing” the current TWA. The data is written to a directory with the TWA’s Label as the directory name. This is “Process 1” in the above “Data Flow Diagram”.
This Icon starts the Spatial Adjustment Manager, carries out “Process 2”, and sets SAM up with numerous defaults ready to step through the processes required.
This is used to write out the Job Scripts. SAM (by default) breaks large areas up into 1km2 tiles, and for larger areas is great for work flows in this part of the over all work flow.
This is used to run the upgrade process on all the 1km2 tiles. The “Iterative Best Guess” algorithm is standard and the “Least Squares Adjustment” algorithm is an optional extra, and are run at this time.
This displays the upgraded features to be displayed over the original. There is a workflow here of “Find, Fix and Forget” involving “Feature Analysis” tab, the Spatial Adjustment Engine and other tools that is not discussed in this article.
This takes the final upgraded features and writes them back to the TWA directory mentioned above, and represents “Process 3” in the above “Data Flow Diagram”.

The user exits the “Spatial Adjustment Manager” and returns to continue with the “SAM Toolbox” mentioned above.
This Icon updates the master themes with the upgraded coordinates relevant for the current TWA, and records points that moved outside the current TWA to ensure they are not moved a second time.
 

With the reduction of spatial, aspatial and temporal aspects when dealing with Shape and Tab files, the SAM Software can be sold for $6,000 inc GST, which represents exceptional value for many users. Trial Licenses are available for 30 days, and represent an excellent way for large GIS users to test SAM before implementing it as a fully integrated process in the GIS IT Environment.

Is this software intuitive, probably not as is automates so many spatial operations some of it may well appear as ‘black box’ functionality, but it is easy to use and not overly challenging to master.

The next phase after “Upgrading Spatially Dependant Layers with a replacement Digital Cadastre” is to move onto “Upgrading Spatially Dependant Layers in a partially upgraded Digital Cadastre”. Space prevents this discussion but please feel free to visit the Spatial Tapestry web site.

When one considers the flow-on advantages of being easily able to catch up with and stay current with the underlying Digital Cadastre, it has to be worth the effort.