Comparison of imagery from repeated survey missions can be a useful source of information, provided that they can be carried out each time under similar conditions.

It is here that Aerodata offers a cost-effective service that is based on a set of criteria of the changes to be monitored.

Examples are:

• tracking recently installed solar collectors
• house extensions, roofs and dormer windows
• tree felling
• dumping of construction waste

The analysis of imagery can be even more effective by using height models of the areas obtained by automatic image correlation or from laser scanning.

Especially for Dutch clients Aerodata is involved in executing BAG mapping projects. BAG is aiming at a completion of the large scale base map of The Netherlands (GBKN) with additional elements in the built-up environment, specifically for use in communes.

In many cases Aerodata is involved in the primary data acquisition for these projects and a logical extension is the BAG mapping.

A project contains 2 phases:

• The first phase is the change detection by comparing the new aerial imagery with existing base maps
• The second phase is the mapping and classification of the new elements for entry into the updated GBKN