Volume 9, Issue 2
Tricks of the Trade
In and Out
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Updating a Geographic Database
The number of geographic databases is increasing rapidly in many domains, varying from municipal management to tourism and archeology: anyone managing a territory needs their own geographic database .
Geographic databases form the data part of geographic information systems (GIS). At the Dutch Cadastre (Land Registration) we have built our own GIS, which is primarily a geographic database with houses and ownership boundaries.
In the beginning, paper maps were digitized as the data source for this geographic database. Now that all existing paper maps are in the database, it is important to keep the database up to date. For example, when a new house is built, the database will be updated (Figure 1). Central to this updating is that we do not want to change the coordinates of the information that is already in the geographic database.
Figure 1. Measuring a new house (the green one) using a theodolite from two different positions.
However, we sometimes did not trust the results of existing update programs, which were coded in FORTRAN. We wondered if our formulae were correctly implemented, or were wrong from the beginning. So we checked our formulae by implementing them in Mathematica before checking the FORTRAN code. In the end the formulae was proven right and we found a bug in the FORTRAN code.
In this article we use this implementation to demonstrate how new information is added to the geographic database.
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