The Mathematica Journal
Volume 9, Issue 2

Search

In This Issue
Articles
Tricks of the Trade
In and Out
Trott's Corner
New Products
New Publications
Calendar
News Bulletins
New Resources
Classifieds

Download This Issue 

About the Journal
Editorial Policy
Staff
Submissions
Subscriptions
Advertising
Back Issues
Contact Information

Updating a Geographic Database
Leendert van Gastel
Harry Uitermark

Warping

When collecting new information--most of the time using a theodolite, which is a surveying instrument that measures bearings and distances--all observations are done in a redundant way. This redundancy makes it possible to check the observations for errors. But at the same time, due to the stochastic nature of measurements, small discrepancies are introduced. So before adding new information to the database, we check our measurements for errors and filter out the small discrepancies by least squares methods. A statistical test is performed to ensure the quality of the data: the covariance of the measurements should be within standardized bounds.

A second stage, called warping, fits this internal local computation into the external global world of the database. There are several methods in use for warping. We mention:

  • A similarity transformation, where the coefficients are determined by interpolation
  • A quadratic bilinear extension
  • An elastic rubber-sheet transformation [2]

At the Dutch Cadastre, we chose the last method because it deals best with the information already in the database. We will illustrate this later with an example.



     
About Mathematica | Download Mathematica Player
Copyright © Wolfram Media, Inc. All rights reserved.