The National Institute of Geographic and Forest Information (IGN) has embarked on the creation of a high definition map of France by Lidar topography. IGN started its Lidar HD program at the end of 2020. This project “aims to cover the territory with a new type of data, Lidar data”as summarized by project manager Loïc Gondol, and must still extend over 5 years. “You have to imagine a cloud of points which represents the surface of the ground and above ground on the whole of French territory”he adds.
This program has a budget of 60 million euros. 50 people within IGN are currently working on it and the team will grow to a maximum of 70 people. The institute relies on four subcontractors for data acquisition and processing.
Planes to collect data
For now, IGN is in the phase of acquiring this data. “The interest is to have data at the national level and to pool the collection”, summarizes Loïc Gondol at L’Usine Digitale. For this, it is necessary to pool the acquisition specifications, which is not necessarily obvious since everyone does not need the same degree of precision. As part of this project, the IGN is aiming for 10 points per m². But Lidars make it possible to go much further and to obtain 100 or 200 points per m².
It is also necessary to define in which season the data will be collected. “With a digital surface model from an acquisition in winter, knowledge of leaves and plant volume is less and not usable for monitoring fires”, explains Loïc Gondol. Concretely, for the collection of data, the IGN has two planes each equipped with a Lidar allowing it to capture information on a determined area. Other data is purchased from service providers.
IGN began by collecting data on priority areas located mainly in the south-east of France (the Alps, the Massif Central, the Pyrenees, Corsica). The institute expects to complete acquiring this raw data over the entire metropolitan and overseas territory (with the exception of Guyana) by the end of 2025.
At the end of this acquisition phase, IGN has a raw point cloud. This is not enough to have a digital model of the terrain. The data obtained must be processed by classifying each point, ie by providing them with semantic information (soil, water, vegetation, building, etc.). “A first part of this data processing is carried out automatically by classification algorithms possibly improved with a little artificial intelligence.” Then, at the end of this first processing, part of the data is manually taken over to refine the classification. This is the case for high-stakes areas where the expected quality is higher, such as urban areas and riversides.
From this cloud of classified points, the IGN plans to derive digital models of the ground, the supersoil and the height. The ground level will include the buildings and the vegetation in height. The digital height model is the difference between the ground and the overground (the information on each pixel will be the height between the two).
The first models will be available at the end of 2022 at the beginning of 2023. IGN is currently setting up the chains to produce them and the necessary tools. “On the processing phase, we are not yet at nominal production rate, which should be 15 months between data acquisition and the end of their processing”, slips Loïc Gondol. As with data collection, processing will be both carried out by IGN and delegated to subcontractors.
Public policy and risk prevention
All data will be freely accessible: the raw point cloud, the classified point cloud and the numerical models. All data is hosted on IGN infrastructure and accessible on Geoplatform. At this level, the interest is also to “mutualize storage and distribution”, according to Loïc Gondol. Users will be able to use it and create services with it if they wish.
Originally, this project aims to help implement public policies in several sectors such as agriculture, forestry, the environment, urban planning and energy. “To pursue and build public policies, it is necessary to have precise and detailed geographical data, abounds Loïc Gondol. This new data repository aims to meet these needs.”
Concretely, this Lidar map aims to improve knowledge of the forest. “In the context of global warming, the national forest office and private managers need to know the state of the forests and how they are changing”, explains the project manager. Today this is achieved with significant field work. Tomorrow, the idea is to have some of this knowledge (state of forests, volume of wood, etc.) through the collection and analysis of Lidar data.
Assessment and monitoring of natural risks
Another example relates to the policy for monitoring and evaluating natural risks, such as the risks of flooding and landslides. To monitor and assess them, it is essential to model the areas at risk. These models could help to carry out simulations and predict possible dangers. “To simulate the height of the water, the way in it flows and by what it is constrained, it is essential to have a fine modeling of the ground”, slips Loïc Gondol. Especially since with global warming, bad weather can occur in unusual places, hence the interest of having a fine map of the territory.
IGN is also convinced that this data can have other uses. The institute intends to carry out information transfers during the spring to all potential users (public, private, associations, etc.). The idea is to specify the content of the data to which they will be able to access and to determine whether the IGN is in phase with the use cases. “New structuring use cases can be identified”adds Loïc Gondol for whom this project is only in its infancy.
If France is not a pioneer on this subject, it is far from being at the back of the pack. The UNITED STATES act in dispersed order at the level of the federated states. Closer to us, the Netherlands are ahead and are already on their third or fourth coverage of the territory. The Swiss makes its second cover. Spain, for its part, embarked on this project at the same time as France. And many countries have not yet embarked on such a project.
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A Lidar map of France soon available for free access
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