WinGap Sketch Conversion Presentation

A NEW LOOK AT PLANIMETRICS
Using CAMA data to create building footprints
while troubleshooting your CAMA database
Jimmy Nolan
The University of Georgia’s
Carl Vinson Institute of Government
Information Technology Outreach Services Division (CVIOG-ITOS)
Why did we choose WinGAP CAMA for our pilot?
• Used by approximately 141 counties in Georgia
• CVIOG-ITOS wrote the WGSketch module and we’re familiar with
the database design
WinGAP Basics
The current version of WinGAP uses a FoxPro database to store information, but a
SQL Server version is in the works.
Why is the database designed like it is?
Assessor data is full of one-to-many, and many-to-one relationships which complicates
the design. For example:
One
to
Person
Parcel
Parcel
House
Many
Houses
Parcels
Many
Owns one or many parcels
Contains none, one, or many houses
Contains none, one, or many accessories (pool, shed, etc.)
Contains none, one, or many porches
to
One
(Lends itself to the use of codes and lookup tables)
Have brick siding (storing a number “3” as a code for brick reduces the database size)
Are classified as residential
What is WGSketch?
Where we are…
Where we want to be…
Why does anyone need building footprints?
Outside the Tax Assessors Office
• Assessment of impervious surface for storm water utility fees
• Emergency services and law enforcement
•Many other analysis processes such as determining housing
density, and encroachment detection
Inside the Tax Assessors Office
• Verification of sketch data by comparing with aerial photos
• Ability to distinguish between multiple improvements on the same
parcel
• One additional way to view assessment data and the only way to
view it in a real world environment
• Footprints can be used for “masking” while doing change
detection
Verification of Sketch Data and Aerial Photo Masking
How were building footprints created and maintained in the past?
Created by digitizing from an aerial photograph, sometimes in stereo and sometimes
not.
Disadvantages:
• Time consuming and expensive
• Visual obstruction by trees and building “canyons”
• Detail about the structural components was lacking
• Building overhang (eaves) could give inflated numbers for area
• Resolution of photos limited digitizing precision
• Had little or no value as an assessment tool
Maintained by having new aerial photos taken and searching for new structures to
digitize.
Disadvantages:
• Could not update until the next aerial photos were taken
• Process of finding new structures lacked intelligence
What do building footprints look like?
The old way…
The new way…
An overlay comparison
Primary Steps of the Conversion Process
• Pack your WinGAP tables (removes records that have been marked for deletion)
• Import WinGAP tables to SQL Server (reorganize data to acceptable format for ET GeoWizard)
• Export a single reorganized table (make compatible with ET GeoWizard)
• Create a table of Parcel numbers and their real world X,Y centroid coordinates
• Join SQL Server exported table to the parcel centroid table based on Parcel#
• Add X values from two different tables together (inflate X sketch coordinates to real world
coordinate values)
• Add Y values from two different tables together (inflate Y sketch coordinates to real world
coordinate values)
• Convert X,Y coordinate pairs into a point layer
• Using ET GeoWizard, convert points to polygons
• Using basic ArcGIS editing tools, move and rotate the sketch into place
Record
Count
37,666
29,701
143,846
After Exporting from SQL Server
Before Importing into SQL Server
Record
Count
716,332
+
=
Inflate the sketch coordinates
with parcel centroid coordinates
This Table
+
This Tool
Gives This Result
Create points from the Final_x
and Final_y coordinates
These Points
+
This Wizard
Using ET GeoWizard, convert points to polygons
=
These Polygons
Using basic ArcGIS editing tools, to move and rotate the sketch into place
Comparisons between the old (yellow) and the new (red)
Missed Deck, Eaves
Possible Addition Missing
Shadows, Eaves
Heavy Tree Canopy Obstruction
Shadows, Eaves
Intelligent Maintenance
The rest of the story…
Shortcomings of the WinGAP conversion process:
• Tax Exempt properties (churches, schools, public buildings) are likely to be
missing
• Anytime an override value is used, the sketch may be missing
• The output is only as good as the input (garbage in = garbage out), and attention
to detail varies from county to county
• Polygon description codes can vary from county to county
• Does not include accessory buildings (yet)
• “Complete” updates are not possible without new aerial photos or more field
measurements
Questions?
Jimmy Nolan
Local Govt. GIS Project Manager
Carl Vinson Institute of Government
jnolan@cviog.itos.uga.edu
Phone: 706-583-0325
Fax: 706-542-6535
1180 E. Broad St.
Athens, GA 30602