Using LiDAR for Emergency Response Planning

 Fire and Emergency New Zealand (FENZ)  have the principal objectives to reduce the incidence of unwanted fires and the associated risk to life and property. To protect and preserve life, and prevent or limit injury, damage to property, land and the environment. By utilizing LiDAR data in New Zealand, they can create 3D building primitives and perform 'location allocation' analysis to estimate response times in emergencies.

As part of FENZ's Aerial Appliance Strategy project, Fire and Emergency used LiDAR and building outlines data from the  LINZ Data Service  to identify buildings with an area over 1000m  ²  or 9m in height. These buildings typically require the attendance of an aerial appliance to battle fires. An aerial appliance is a specialized emergency vehicle that has a large ladder that hydraulically rises to suppress fire and/or effect rescue.

There are several steps to achieving the result, but it is ultimately some simple mathematics to extract the building height information. By subtracting the DEM (ground elevation) from the DSM (above ground elevation) the remainder is feature height which is transferred to the building footprint data.

When extracting the building height from the LiDAR there are multiple methods to find the height value, using the average, maximum, minimum or the center point inside the building outline, all could provide a different building height. For the FENZ GIS team, they were asked to detect buildings over 9m in height and using the maximum value in the extraction process ensures they identify every building that meets their analysis criteria.

Some building outlines were identified as having no height available due to differences between the LiDAR data and building polygons. For example, a new building may have been constructed and the outline may exist within the layer, but the LiDAR isn't recent enough to have surveyed the building, therefor no height value can be assigned to the building polygon in the height extraction process.

In some cases, false positives are introduced by the process which attribute the building with incorrect height values. While easy to remedy, they are 'false positives' and are harder to detect than features with no height information and these require ongoing remedial actions to remedy. This occurred where the New Zealand Post House Building (7 Waterloo Quay) was assigned the height value of 6m from the Wellington LiDAR 2019-2020, despite having a height value of over 60m in some sections.

The next steps will be to further develop and process additional cities when available, with a view towards developing a simple digital twin that can better inform emergency response planning within FENZ. There is also the desire to improve the road network that supports this process, this will provide a higher level of detail and accuracy when estimating travel time to fire emergencies.

Currently the 3D structure is a single block polygon and doesn't show the true shape of the building, further utilizing the LiDAR to show sections of the building that protrudes and recedes can also help to add a higher level of detail to the modelling. Increasing the level of detail in the 3D extraction process can help identify the optimal positions for the aerial appliance to position to fight the fire before even arriving at the scene.

 https://www.fireandemergency.nz/  - Fire and Emergency New Zealand

 https://data.linz.govt.nz/  - LINZ Data Service

If you have a LiDAR story you'd like to share, please get in touch: elevation@linz.govt.nz