How to generate a TINrelief from an FBX file using FME?

I’m curious as to why you want your Terrain in CtiyGML

What does your FBX look like? I’m guessing it’s already a 3D Mesh?

I’m not really sure of many applications which support goespatial analysis conducted on a CityGML terrain directly. 

It really depends on what you want to do with your data as to what format it needs to be in.

 

Hello Matt, thanks for your reply.

Actually, at the current stage of my project, I just wanted to display the building and bridges in CityGML together with a terrain. I was just thinking whether this action requires all models to be a CityGML format as I saw there are encodings for Relief module in CityGML?

For long term, I think maybe a CityGML terrain may help in conducting analysis on cut/fill volume for engineering works? Or maybe flooding analysis?

I deeply appreciate your reply.

What tool would you be using to display the data?

The TIN would be the most realistic way to “display” the data as it’s 3D, rather than a Raster which is just an image - depending on the visualization platform you are using the CityGML data will likely need to be converted into an internal format which means that a Geotiff may be a valid approach. If youf FBX is already in 3D though the best thing it to probably try and preserve the model as it is.

To create a CityGML TINRelief with FME you’ll need to make sure your FBX is georeferenced, or at least figure out a way to georeferenced the data. 

Once the data are georeferenced then you can follow this guide on how to get started with writing out CityGML: https://docs.safe.com/fme/html/FME-Form-Documentation/FME-ReadersWriters/citygml/Tutorial/writing_citygml_from_fme.htm

 

Hello Matt. Thanks for your reply again!

I am currently using FZKViewer to visualize the CityGML models. But I found that its performance would be poor when loading a .gml file containing multiple CityGML models. Is there any software/viewer that you recommend to view the CityGML models?

And thanks for the link that you provided. I will be working on it. 

Thank you very much!

Yeah, CityGML is typically a format which is used to exchange/distribute data. A common destination for CityGML city models for visualization is usually something like CesiumJS (3DTiles) or ESRI’s I3S format.

The FZK viewer is probably the best tool for viewing an inspecting CityGML data at a small scale because it probably supports most (if not all) features of CityGML, however, it is limited when datasets get to big, similar with FME. 

Here’s a 3D application which is visualizing 3DTiles: https://www.3drotterdam.nl/ on CesiumJS based application. The 3DTiles were created/converted from CityGML data. The one exception is the terrain which was likely created from an OBJ or a GeoTiff instead of CityGML, although it may have been created from a CityGML terrain. CityGML terrain is seldom used because having a terrain in CityGML doesn't really provide many benefits over other alternatives because there isn’t much in the way of semantic structure, it’s mostly just the geometry. 

Gaming engines are also becoming popular tools for visualizing city model data - usually, however, this is also done with 3D Tiles or I3S.

I guess the typical use/workflow for city scale data is something like this:

1. Data are modelled in a 3D modelling tool (There are a number which are good for lowpoly/city-scale data). Typically data should be modelled already with the CityGML data model in mind but may not produce CityGML at first. This modelling is usually done by or at the cost of the authorities (but not always).

2. Data are converted to CityGML for distribution - CityGML is common because it is one of the very few open standards in the 3D GIS world with semantic structure. Again, this is usually done by the authorities. Distribution of terrain data as CityGML (or in 3D at all) is much less common as the terrain often has many use cases in the 2D realm as well is is usually limited to GeoTiff. I do think this is changing a bit now though, we may start to see the authorities created processed 3D terrain datasets for distribution in the near future.  

3. CityGML data then can act as one of the base datasets which gets used in applications, e.g., visualisation, simulations, calculations. I like to think of CityGML data as forms of processed raw data. Indeed there are many who want to convert CityGML into FBX for use in various CAD or 3D modelling applications.

Sorry about the essay, and you likely know much of this already but my point is really that CityGML isn’t typically used directly in applications but is rather a data model used to help exchange data.


  

 

Hello Matt!

Please don’t feel sorry about the paragraphs. They are absolutely great point of views and I learn a lot from your words. Thank you so much for providing me with so many fruitful insights and opinions!