[x3d-public] Google maps 3D (size) in VRML format (.wrl) textfile, for instance for London?

[Leonard Daly]

Hi Daniel,

My very rough calculation would go something like

BuildingSIze = 100B + (50B/face * #-faces)

Where 100B is a WAG on the number of bytes needed for the face 
definition (Transform, etc.). As the number of faces of a building 
grows, this number doesn't matter.

50B/face assumes 3-4 vertices per face and includes the space required 
by the vertex definition and index referencing (thinking of 
IndexFaceSet). Some space would be saved by using one of the Triangle* 
nodes.

#-faces is really how finely you want to model the building. If every 
building is a rectangle, there there are 5 faces. If you want to model 
sloped roofs or other architectural features, it will be more. If you 
need higher resolution to show windows, doors, or curved surfaces, it 
will be a lot more.

I am not familiar with the sizes or dimensions of "Greater London Zone 
1-6". A quick google search indicates that looks like it means a 
diameter of 2-32 miles. Using this scale at Zone 1, each pixel (assuming 
2000 pixels across) is ~1m. This means that buildings would be modeled 
rather coarsely. If there are 20 faces per building (complete guess), 
that means each building takes ~1KB. If the footprint of each building 
averaged 100m^2, that give 800 buildings on a 3.2km circle (assuming 
dense pack of buildings - i.e., no roads). That is about 1MB.

If you keep all of the detail as you go through each zone, then Zone 6 
is 16x^2 bigger giving a total size of ~250MB.


It may not be possible to handle the display in any reasonable time. You 
may need to break things up into smaller blocks. 3D Tiles (and its 
successor 3D Tiles Next) both support Hierarchical Level Of Detail 
(HLOD). These allow the display of the entire globe at whatever detail 
you desire. Those systems do not use X3D/VRML, but glTF as the leaf 
nodes. X3D does import glTF, but I do not believe that it intrinsically 
supports an HLOD system.


Leonard Daly



On 10/24/2022 3:58 PM, Daniel Alexandre wrote:
> I need to have someone make a good estimation of how many megabytes 
> would be a file in the format of VRML 2 (extension .wrl) in a static 
> text file for the 3D representation of a kind of Google 3D map of 
> "Greater London (Zone 1 to zone 6!)", in the United Kingdom, given 
> that that representation would only use the box (parallelepiped 
> facade) and would be a bit like the plaster mockup in miniature of an 
> urban city of an architect in reasonable accuracy featuring buildings 
> and their facades (that are not particularly high) and the large 
> amounts of roads and parks that are basically empty... How many 
> gigabytes would that static text file in .wrl format be? Roughly. A 
> good estimation is needed. You can calculate it for a good area 
> neighborhood and then multiply it for the whole area or something like 
> that.
>
> Just assume there are no buildings like the Shard and ignore that 
> level of finesse in the details of the facades of the buildings. We 
> want a quite rough estimation to have an idea of how big would be the 
> static data of the textfiles. If you can come up with a number with 
> your own rough calculations in a couple of minutes would be indeed 
> helpful. Would you say the .wrl file would be bigger than 1 Gigabyte 
> for London (Zone 1-6)? Would you say the file is between 1-500 Gb? 
> What is your best quick rough estimation? That will be helpful and I 
> will, later on, be willing to compare notes if I do other calculations 
> myself.
>
> - Daniel
>
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