Polyline with altitude ground behavior tool and question

CesiumJS
1

Hi,

I noticed that the behavior of polylines whose endpoint is elevated above ground appears to have been discussed in s community post and that that post referenced this issue. The issue is open, but I thought I’d mention them here in case there’s a quick solution to what I’m seeing now.

When I map polylines in czml that have enpoints or midpoints with a non-zero altitude, their initial point on the ground, demarked with altitude 0 as shown below, doesn’t clamp to the ground. Here’s an example of a polyline definition:

{
    "id":"f2n7wpo",
    "name":"n7wpo",
    "description":"<H2>n7wpo</H2><table><tr><td>datetime2 = 2025-02-16T02:09:28</td></tr><tr><td>rst = 559</td></tr></table>",
    "polyline":{
      "positions":{
        "cartographicDegrees":[-122.39556128064362,37.79932829961188,-5, -122.77430903389264,42.95907274855483,301000]
      },
      "material":{
        "solidColor":{
          "color":{
            "rgba":[0,255,0,255]
          }
        }
      },
      "show":[
          {
              "interval":"2025-02-16T02:08:28Z/2025-02-16T02:08:46Z",
              "boolean":true
          }
      ],
      
      "width":5,
      "relativeToGround":true
    }
  },

You can see the behavior on this map .

When you zoom in, notice that the polylines that ascend into space are not on the ground.

In this example, the polylines were orignally below ground when specified with a 0 altitude starting point:

image
image961×707 75 KB

Is there a flag to set for polylines that will clamp their origin point to ground level?

In the mean time, I used ChatGPT to develop JavaScript code that provdies altitude adjustment so I can move the lines up or down till they do start on the ground, and then save the updated czml. Here’s a video of the code in action.

Thanks,
Hamilton Carter

2

Hi @antigrav_kids, I’m seeing some issues and threads that make me question whether KML is working at all with “relativeToGround” and a terrain.

Can you verify this on your end? If your KML specifies a constant height of (say) 10m, does it follow the terrain at all? If not, you could open an issue in the repo.

Your altitude adjustment code is an impressive workaround!

3

Thanks @jjhembd !

I should have been more clear. For use with Cesium, I’ve switched all my maps over to czml. I do see now that the issue referenced might have been discussing using JavaScript to work around a kml issue.

The behavior I’m seeing though, is generated by a czml map read into Cesium.

Best Regards,
Hamilton Carter