3D BAG Accuracy: Analyzing Height Variations In Eindhoven
Navigating the Nuances: Interesting Cases in Eindhoven for 3D BAG
Hey 3D BAG team! Following your insightful presentation on Geomatics Day, I wanted to share some observations regarding the representation of building heights in the 3D BAG, particularly focusing on the city of Eindhoven. It seems that the current 3D BAG model often places each building at a single ground level (maaiveld) value. However, in Eindhoven, and I suspect in many other urban areas, we encounter situations where the maaiveld varies significantly across different sides of the same building. This presents a unique challenge in accurately representing the built environment and its complexities. Let's dive into some specific examples and discuss the potential implications for the 3D BAG's accuracy and usability. It's like, imagine a building that's built on a slope – how do you accurately represent that in a 3D model?
Treurenburgstraat 271: A Tale of Two Ground Levels
Let's start with an example: the building located at Treurenburgstraat 271 (object ID: 0772100001022085). You can check it out on the BAG viewer. The situation here is quite illustrative. The parking lot beneath the buildings isn't considered a BAG building because it's an 'open' structure. The buildings above are aligned with the maaiveld at the front of the structure, but this doesn't reflect the varying ground levels at the back. It's kind of like the model flattens the building onto a single plane, which doesn't capture the real-world scenario.
Here's a visual to help illustrate the point. The front of the building appears to align with the ground level, while the back, which may sit above a parking area, doesn't. This can be problematic for things like flood risk assessments, where the exact ground level is super important. The oblique view clearly shows sheds that are elevated above the primary ground level, again highlighting the multi-level nature of the site. This discrepancy underscores the challenge of representing complex building layouts in a simplified 3D model. How do you decide what maaiveld value to use? And, how does this impact the usefulness of the 3D BAG?
Compare that to the Esri version of the 3D BAG (ArcGIS - 3D BAG RD (tudelft3d en 3DGI) en aanvullende panden (Esri Nederland)). In this model, you can see some buildings that appear to 'float' to reflect the varying levels. This might be a better representation of reality, but it also comes with its own set of challenges, like how to consistently and accurately determine those different levels. These differences show that even with the best intentions, representing reality in 3D is complicated. The choice of how to represent these variations has implications for the overall accuracy and usefulness of the 3D BAG, particularly in applications like urban planning and infrastructure management.
Kennedyplein 100: Multiple Solids and Missing Buildings
Let's move on to another intriguing example: Kennedyplein 100 in Eindhoven (object ID: 0772100000354500). If you take a look, you'll see a few interesting quirks in the 3D BAG representation. It appears that there are two solids occupying the same location. And some of the smaller buildings seem to be missing altogether. It's like the model has some overlaps and gaps, making the 3D representation less accurate. These inconsistencies could arise from various factors, such as the data acquisition methods, processing techniques, or the simplification process used to create the 3D BAG.
One side of the building, which provides access to a parking lot (Kennedyplein 400), shows the smaller buildings at the same level as the sidewalk. However, the other side of the building complex, where the parking lot is located (and not included in the 3D BAG), is at sidewalk level. The entrances to the buildings are then on a 'second' maaiveld. This creates a disconnect between the 3D model and the actual physical layout. For users relying on the 3D BAG for navigation or spatial analysis, such discrepancies can lead to confusion and inaccuracies. It is crucial to address these issues to ensure the 3D BAG remains a reliable resource for various applications.
Meergras 1: A Repeating Pattern
The pattern continues at Meergras 1 (object ID: 0772100001027053) in Eindhoven. You can explore it on the BAG viewer. Here, we observe a similar issue where the ground level varies. On one side, the maaiveld is situated on top of a parking lot, and on the other, the building entrances are at a different level. This recurring theme suggests that the single-maaiveld approach may not be ideal for representing buildings in areas with significant ground level variations. The discrepancies between the model and reality could be particularly problematic for users in urban planning or construction. Imagine using the 3D BAG to model a new building – the inaccuracies in the underlying ground levels could lead to significant errors in the project.
I totally get it; accurately representing these diverse situations in a 3D model is complex, and we face similar challenges in our BGT. Because you mentioned you're looking into overhangs, and these examples touch on similar issues, I figured I'd share them. Extra test cases never hurt, right? Who knows, maybe these examples can inform future 3D BAG developments. I hope this helps; let me know if you have any questions!
Best regards,
Celine Jansen Senior Advisor Geo-Information