Geometry with custom triangles/normals

CesiumJS
1

Hi,

I have custom 3D geometry that is already split into indexed triangles with pre-calculated normals. What is the best way to get this data into cesium. I looked at the polygon entities but that seems like it just takes a raw set of points and does triangulation on the points.

Thanks for the help.

2

Hello,

I don’t think there isn’t anything built into Cesium that would handle this kind of input. You could write your own Custom Geometry to handle this.

This tutorial might be a little out of date, but it will give you a good idea of how to write a custom geometry type: https://github.com/AnalyticalGraphicsInc/cesium/wiki/Geometry-and-Appearances

You can also find more information about Geometry and Appearances here: http://cesiumjs.org/2013/11/04/Geometry-and-Appearances/

If you have any questions, I’d be happy to help.

-Hannah

3

We have a task to display radar domes along with jammers. The resulting polygons would be described as free form or irregular3D objects I guess. Basically, we would be given a list of triangles from the output of some application, and then would need to render those triangles.

Questions:

To do this in Cesium:

Would we still need to write a custom Geometry, or has something changed?

Could the triangles be defined in KML and then loaded into Cesium?

I guess we could write the triangles out into a gltf file?

If anyone has any ideas/advice on how we could render these types of objects then it would be great to hear from you!

TIA,

Scott

4

Hey Scott,

I think defining your own geometry is still the go-to way, that way you have full control over the vertices/geometry. Although just exporting it as a KML/glTF would probably work as well!

5

If the kml route is an option then what Cesium object renders the triangles?

6

It looks like KML in Cesium is created with entities (see https://github.com/AnalyticalGraphicsInc/cesium/blob/master/Source/DataSources/KmlDataSource.js#L348), and entities in Cesium are implemented with primitives under the hood, so it would be Cesium’s engine setting up the geometry/vertices/indices.

Does that answer your question?

7

You are correct that there isn’t any support in Cesium for the polygons you describe. I see three options:

  1. Implement your own shaders for your custom geometry.
  2. Put your custom geometry into a GLTF model.
  3. Investigate using the STK Web Visualization Library that is sold by AGI (the company that started CesiumJS).
    Scott
8

Yes that does answer the question.

I’m going the gltf route since that seems like the best fit. I think the KML route would mean each triangle would be an Entity which doesn’t sound like a good way to go. I’ve got most of the code written but I need to figure out the accessors and bufferViews sections, and then I should be done. Thanks for your help!

Scott