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Our issues with CityGML v3

Hugo Ledoux
September 12, 2018

Our issues with CityGML v3

Presentation summarising the issues that TU Delft (https://3d.bk.tudelft.nl), Geonovum (https://www.geonovum.nl), NUS (https://www.arch.nus.edu.sg), and NL Kadaster (https://www.kadaster.nl) have with the current development with the version 3 of CityGML (https://www.citygml.org).

Presented at the 108th OGC Technical Committee meeting in Stuttgart, Germany

Hugo Ledoux

September 12, 2018

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  1. 2 • We collaborate a lot with practitioners inside and

    outside NL; and have lot of own implementation experiences with CityGML 2.0 • CityGML v2 is complete, but complex, and therefore not always easy to implement • community is looking at us to improve • our concerns for a simple, implementable 3D standard -> this presentation • raised issues in SWG and discussed with OGC staff, SGW chairs, SWG members, OGC members
  2. Background: Geonovum & 3D ▪ 2010 – 2018: pilots, experiments,

    … ▪ 2019 / 2020: need for national 3D standards – 3D base data set of NL ~ 1:1.000 – 3D input models for noise analysis – local governments need alignment / interoperability – Hence: the need for 3D standardisation ▪ Geonovum has to advise the Ministry on these standards
  3. Current position ▪ I want to advise CityGML 3.0 ▪

    But, I need a standard that: – avoids complexity as much as possible – can be implemented easily and will be implemented widely – reduces file sizes as much as possible ▪ and – consensus that CityGML 3.0 has these characteristics.
  4. My problem ▪ I cannot form my final opinion without:

    – discussion in the SWG on pros and cons of design choices (both IRL and on mailing list and Github) – implementation experiments to validate assumptions on characteristics – test data sets illustrating how certain concepts will work in practice.
  5. The pudding analogy ▪ So, if CityGML 3.0 is the

    pudding, I see: – people working hard on the recipe for the pudding – virtually no discussion on the recipe, thus making it hard for others to contribute to the recipe – virtually no test samples of the pudding – the wish to decide on the recipe, before it is used to actually bake the pudding – the wish to decide on the recipe based on a timeline rather than on its taste
  6. My position: let’s bake and taste (a lot)! ▪ E.g.

    Is CityGML 3.0 easy to implement? Let’s find out first!
  7. summary of our issues 9 1. current process is not

    democratic/transparent 2. new features add complexity: worth it? 3. Software should be part of the process ! we thus fear usability and adoption by practitioners will diminish (and it is already an issue) This is a summary of an email thread on the CityGML-SWG list entitled ‘Reconsideration of the concept of “spaces” in CityGML v3?’ from June 2018
  8. 1. process not transparent 11 • only ~final results presented

    at SWG meetings • UML and datasets online often weeks after meeting • presentations are directly followed by votes • no time for community to review and understand key concepts • GitHub “Issues” was just activated, but in our opinion this is not how it is meant to work
  9. –Steve Smyth, 20min ago “We begin with Change Request” 15

    • CR are a massive step: they mean highlighting what has been done is wrong. • Issues can be constructive suggestion • few CRs, 15+ Issues in last days
  10. • GitHub == unique hub for all work-in-progress + discussions

    • not used to upload final results, it is the dev hub where *everything* is stored (yes also work-in-progress) • Questions? Bugs? Comments? —> Issue • SWG meetings can only discuss stuff that has been made available beforehand 16 Solution #1
  11. 2. new features add complexity: worth it? 18 • more

    features ≠ improvement • adding features == extra complexity for: • developers: need to update/change code • practitioners: need to understand the new features • “good design is as little as possible”
  12. 2. “Spaces” add complexity: worth it? 19 • new concept

    “Spaces” adds complexity • it has not been explained nor tested yet • we do not know what problem they solve • seem focused on minor issues; most applications do not need them • before there can be a vote, there should be a debate based on facts see GitHub issue #13 for a nice example
  13. 2. “Spaces” solving integration BIM-CityGML? 21 • diff geometrical paradigms

    used (CSG vs b-rep) • outer walls/surfaces cannot be automatically identified • rooms, walls as surfaces (part of a building volume) do not exist as concept in IFC
  14. 2. new Core Module is getting many new things 22

    • “Spaces” • Dynamizers • Point clouds (which can be used to represent a building: LAS/LAZ reader now mandatory if one wants to support CityGML v3) Volker Coors opened issues related to these
  15. • Not aiming at adding features, but stripping CityGML from

    features not used in practice • Presentation about Spaces’ (and other potential features) pros and cons, both from a modeller’s and developer’s point-of-view • We think CityGML should not model all aspects of our 3D reality, we are fine with subset if they mean a usable exchange format 23 Solution #2
  16. 3. Software should be part of the process (1/3) 25

    • there are no (real) datasets and no software capable to read CityGML v3 • neither was planned before the vote for CityGML v3, because only the data model is up for vote • UML models are abstract beast, to know if they work in practice they need to be tested • W3C would never accepts a standard w/o data+software
  17. i p.m FINE fib T9z n.tw y v3 EEN her

    UML released idea model standard i E i finite.no software data q 3. Software should be part of the process (2/3) 26
  18. 3. Software should be part of the process (3/3) 27

    • claims that v3 will simplify the life of developers are unfounded and unproven • there are no complete Python or Javascript or C++ parser known to us (also for CityGML v2!) • most developers do not want to replicate the whole CityGML data model, they use CityGML as an exchange format: they parse a file to extract only what they need Volker Coors mentioned this too in his email in German on Monday
  19. Quiz: What software would allow me to do this? 28

    Take a given CityGML v2 file and: 1. remove one building and replace it by a newer construction; 2. remove all textures (we want to use the model for visibility analysis and these not necessary); 3. save the file to a new CityGML file. • only citygml4j + 3dcitydb • perhaps FME (but need to build that complex workspace) • ArcGIS does not work for this
  20. Rotterdam & CityGML 30 • central hub is all CityGML

    (3dcitydb used) • however, none of the departments have software supporting CityGML • spatial planning, pipelines, maintenance, etc. all use software they are used to • FME used for conversion -> if users want to modify or edit data, it can’t be written back to the CityGML database • employees think this is a problem CityGML is an exchange format that is used in different apps
  21. • software+datasets are mandatory part of the process to develop

    CityGML v3 • allow “profiles” of CityGML to support the most important parts • thus: release of v3 must be postponed (since it’ll take some time to get there) 31 Solution #3
  22. Summary 32 1. More transparency and democracy in the process

    -> GitHub used actively (not only every 3mo) 2. New features: explanation and are they really needed by community? 3. Software part of development process -> postpone the release of v3
  23. CityJSON: TUDelft’s way to contribute 34 • several NL companies,

    governments, and organisations already started investigating CityJSON • flat-schema, compact (~7X compacter), Python/javascript/etc parsers are easy • we already have many software support (visualisation, validation, manipulation, QGIS, web-parser, etc.)
  24. thank you. Hugo Ledoux Jantien Stoter Linda van den Brink

    Friso Penninga Patrick Janssen Filip Biljecki