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How Does CityEngine Generate Vertex Positions from OSM Data?

MichaelGharbharan

I'm assuming CityEngine is projecting the WGS84 latitude and longitude values from the .osm file to another coordinate system.

Does anyone what coordinate system CityEngine is converting the latitude and longitude to?
Also if you know the math or have the code to perform this transformation, I'd really appreciate you sharing it with me.

Thanks.

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MatthiasBuehler1

Hi,

No, that is not possible since the 'tree structure' is created based during the model generation.

Mainly, the 'Model Hierarchy' and the material merging settings in the export settings define that behavior. The shape group option basically adds transformation nodes to group the objects accordingly.

Ok ?

M.

MichaelGharbharan

Sorry, I meant to ask "Is it possible to force a shape to the the child of another shape?"
Right now when I export my models and open them in Maya or Unity I just get a list of all the shapes in the model. If I check the group shapes button in the exporter then it groups all the shapes for a street segment together (the street shape is the parent).

I am wondering if it is possible to manually specify the parent for a shape, so I can control how shapes are grouped together.

Thanks.

P.S your a legend

MatthiasBuehler1

Hi, yes I am .. 🙂

Can you rephrase this a bit ? 🙂

Is it possible to for a shape to the the child of another shape?

MichaelGharbharan

Whoa you're the guy from the tutorial videos!

Using the Model Hierarchy was very helpful. Is it possible to for a shape to the the child of another shape?

MatthiasBuehler1

Hi,

there's a compass in the viewport available. Activate it via d,a ( also check the viewport display settings cogwheel menu )

as far as I remember, in the code, the orientation of the cars are either 0 or 1 ( right or left lane ). But you may want to be more precise, so report the same position as the actual car.

search for i(), where the actual car is inserted on the geometry. the orientation is actually defined by the alignment of the scope to the split street geometry, but you can get the world orientation (cartesian grid) with the convert() function.

Please watch the video here, it'll help to track down where the cars are inserted, using the 'Model Hierarchy' :
http://forums.arcgis.com/threads/44417-CGA-Understanding-the-concept-of-the-scope

Ok ?

Matt

MichaelGharbharan

Hi,

Okay I see. I suppose my best bet would be to generate markers based on the orientation of the cars.

Does this logic seem about right to you (American roads):

If (car is facing north || car is facing east)
placeMarker on right
If (car is facing south || car is facing west)
placeMarker on left

The question now is: how can I determine the direction of a car in the rule file?

Are these fair assumptions to make:
X points North, -X points south
Y points up, -Y points down
Z points East, -Z points west

MatthiasBuehler1

Hi !

When street segments meet that have different widths, an additional trapezoid shape is inserted to compensate. Those shapes usually create unrealistic models of streets, since lanes would be merging in real world. But the UVs are stretched in that region and the first edge of that geometry is angled, so in CE there's no solution for this issue. The best you can do is avoid streets with different widths.

So that's an unsolved issue in 2012. But we've been working on the street system for 2013. Though I'm not perfectly sure if this specific issue will be adressed.

Ok so far ?

m.

MichaelGharbharan

I've been investigating this problem and I think I may have stumbled upon a bug (or maybe there's a button I forgot to press)...

[ATTACH=CONFIG]26742[/ATTACH]

The image above shows a shape that is not properly orientated. This shape was generated using the polygon street creation tool. Judging by the misalignment of the lane textures, it is very apparent that the shape is not rotated correctly (or maybe the UVs are flipped...?)

I tried rotating the object manually on the y axis by 180 degrees (to align the textures) but it would not let me, as the image below shows.

[ATTACH=CONFIG]26743[/ATTACH]

However I am able to rotate the two shapes that are adjacent to it. Although I did not expect this to work, I rotated one of the adjacent shapes by a very small amount and it fixed the problem shape (which is what leads me to believe there might be a bug).

[ATTACH=CONFIG]26744[/ATTACH]

EDIT: Looking at the first image of my post above this one, if you follow the lanes in the yellow box to the left it is very apparent that there is an issue with street shape alignment...the scene from this image is from the Modern Streets example.

Hey,

That worked perfectly. However there are some inconsistencies with the marker production, see image below:

[ATTACH=CONFIG]26631[/ATTACH]

In the areas in the yellow boxes, you can see that the markers are not consistently being generated on the correct side of the road. I am trying to generate markers only for the left side of the road.

Interestingly though, the cars are still orientated correctly in CityEngine.

[ATTACH=CONFIG]26632[/ATTACH]

Do you have any ideas why the markers aren't properly being generated?

Some background: I am using these markers to create traffic AI in Unity and by having "left" markers and "right" markers I am able to direct the direction of traffic flow, however this requires the markers to be consistently generated on the correct side of the road.

Another approach I could take is exporting whatever data the cars are using to properly orientate themselves.

Any help you can offer would be appreciated.

Thank you.

34725markers.png

markers.png

MatthiasBuehler1

hi,

I'd add an attr :

@Range("streets", "markers")
attr exportWhat = "streets"

then on each of the leaf shapes which actually create geometry, NIL them accorsing to that new attr.

e.g. if you only want to export the streets, NIL the markers.

if you have that setup, export TWICE. once for the street geo, once for the markers.

m.

MichaelGharbharan

Hello,

The exported model is indeed rotated, not sure why this is but I was able to place objects on the marker positions by writing a script in Unity which places the objects based on the marker's vertices.

Now I've got another question for you 🙂

I need a way to be able to only export the markers and the shape they are parented to. I realize my wording to describe what I want to might be a little confusing, so I have made some diagrams to try and explain:

The image below shows how the imported city appears in Unity.
[ATTACH=CONFIG]26072[/ATTACH]

The image below shows what I am trying to get imported into Unity.
[ATTACH=CONFIG]26073[/ATTACH]

Is this even possible? Please let me know if you have any thoughts.

Thanks.

EDIT: Forgot to mention, I had the thought of editing the rule file so that it only generates what I want, but I'm inexperienced with writing rule files and not sure if this is plausible.

export2.png

export1.png

MatthiasBuehler1

hey man,

short fix :
ignore the difference and just use the point marker geometries in Unity. Write a js or cs script to extract the data in Unity instead of CE.

long fix :
not sure what could cause this.. weird. it seems the data is also rotated.. could it be you have somehow inverted some axes, e.g. x = -123456 instead of 123456 ?

try to track this down on a very simple 1 meter wide / 10 meter long street, so you can precisely control all point marker vertices.

I've done a similar thing some time ago in Maya and it did fit spot-on.

lemme know.

matt

MichaelGharbharan

Hello,

Thanks for all your help, I was able to generate the markers. I've exported the city as in FBX and imported it into Unity. I am now trying to spawn objects on the marker positions but the positions are off (see image below).

[ATTACH=CONFIG]25986[/ATTACH]

Referring to your post:
http://forums.arcgis.com/threads/64088-Vehicle-placement-on-CityEngine-generated-streets.?p=225246&viewfull=1#post225246

I am offsetting the marker positions using the values given from the FBX exporter (see image below)

[ATTACH=CONFIG]25985[/ATTACH]

I am subtracting the offsets from the marker position in the markerInstances.py script (see image below)

[ATTACH=CONFIG]25988[/ATTACH]

Do you have any ideas why my object placement positions are off? I've been trying to figure out the method CityEngine uses to calculate its offsets but I've been unable to recreate the same offsets.

Hi !

the marker reporting is in the CGA rule which creates the street geometries. In the example in the other thread I used the 'Modern Streets' example, which you can download.

The format to export is basically just a text list. E.g. you can write this into a text file. Since you're creating the text on your own, you can compose directly any other ascii file format. very flexible.

Makes sense ?

MichaelGharbharan

Something tells me you want to go in this direction .. 😉

http://forums.arcgis.com/threads/64088-Vehicle-placement-on-CityEngine-generated-streets.

That is definitely the direction I want to go in!

http://forums.arcgis.com/threads/64088-Vehicle-placement-on-CityEngine-generated-streets.?p=225535&viewfull=1#post225535

That post you made seems like it would be a great starting step for me but I have a couple of questions:

Where do I put the code for the marker creation and position reports?
What format will the data exported by the markerInstances.py script be in?

Thanks.

MatthiasBuehler1

Something tells me you want to go in this direction .. 😉

http://forums.arcgis.com/threads/64088-Vehicle-placement-on-CityEngine-generated-streets.

MichaelGharbharan

Thanks for your response,

Let me give you some background on what I'm trying to do. I want to use CityEngine to generate a 3D model from an OSM file then I want to import that model into Unity, parse the OSM file myself (in Unity) and do a little bit of math to position the nodes from the OSM in the correct place on the model generated from CityEngine.

However in order for me to do that, I need to know about the projection CityEngine does so I can ensure the nodes are put in the correct space.

If you cannot share CityEngine's secret recipe with me, I can think of one other solution, but I'm not sure if its possible:

Writing an exporter for CityEngine to output the node data (see image) to a file, this way I could just load the node positions from file rather than projecting them myself.

[ATTACH=CONFIG]25624[/ATTACH]

Is it possible to export the data in the image above? If so can you give me some direction?

Thanks.

node.png

MatthiasBuehler1

Hi !

The lat/long values are projected to CityEngine's cartesian coordinate system, thus the high vertex coordinate values. CityEngine stores all the vertex positions in cartesian coordinates.

The projection is done with a library, but I'm not sure how, but I'm pretty sure we can not share this. I'd recommend you google how to do this if you need the code.

Let me know if this is ok or if you need more info.

Matt

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