CZML: Paths that "followSurface"

CesiumJS
1

I'm working on an app that will plot out WWII submarine patrol reports. So far, Cesium's been an absolute pleasure to work with, but I've run into a bit of a problem that I'm hoping someone could give me a hand with.

I've plotted out the routes with a polyline that offers the awesome "followSurface" property. This is really useful, because the patrols go back and forth across the Pacific Ocean, and there is sometimes about a month between points.

I've got a 3D submarine model rendered on the map that I'd like to have following the path. I've got it working almost perfectly, except there doesn't seem to be a followSurface property for the CZML path, causing the model to take a straight line through the center of the ocean (While going underwater is a thing subs tend to do, this isn't ideal for showing the position.)

I can interpolate points myself, but then I have to balance between processing power/bandwidth/Database storage and resolution: 100/1000 intermediate points vs. 2 points... I was hoping there would be a way to make the path an arc instead of a straight line.

Thanks in advance for any help!

What I've got now:

...

var builtInCzml = [{
    "id" : "document",
    "version" : "1.0",
    "clock" : {
      "interval" : "1942-02-03T16:00:00Z/1942-02-03T16:04:00Z",
      "currentTime" : "1942-02-03T16:00:00Z",
      "multiplier" : 1,
      "range" : "LOOP_STOP",
      "step" : "SYSTEM_CLOCK_MULTIPLIER"
    }
}, {
    "id" : "Vehicle",
    "availability" : "1942-02-03T16:00:00Z/1942-02-03T16:04:00Z",
    "model" : {
        "show" : true,
        "gltf" : 'js/cesium/models/sub.glb',
    },

    "label" : {
        "fillColor" : {
            "rgba" : [255, 255, 0, 255]
        },
        "font" : "bold 10pt Segoe UI Semibold",
        "horizontalOrigin" : "LEFT",
        "outlineColor" : {
            "rgba" : [0, 0, 0, 255]
        },
        "pixelOffset" : {
            "cartesian2" : [10.0, 0.0]
        },
        "scale" : 1.0,
        "show" : true,
        "style" : "FILL",
        "text" : "USS Narwhal",
        "verticalOrigin" : "CENTER"
    },
    "position" : {
        "interpolationAlgorithm" : "LAGRANGE",
        "interpolationDegree" : 1,
        "epoch" : "2012-08-04T16:00:00Z",
        "cartesian" : [
          0, -5509722.586460211, -2151844.221882823, -2378299.9406736423,
           18, -5684531.161035097, -2744542.9854255156, -910990.3759759372,
           100, -4396545.545638362, -2437044.991071697, 3912790.1338688354,
           108, -4171451.1216227254, -2304348.5076655983, 4224994.521149366,
           108, -4171451.1216227254, -2304348.5076655983, 4224994.521149366,
           132, -3557603.9416444204, -1978781.4385709134, 4893709.012974627,
           132, -3543403.8974256907, -1933264.1334437176, 4921932.675781873,
           136, -3462736.6795682968, -1899722.395552415, 4991443.492328856,
           140, -3532251.61244064, -1853162.7889278433, 4960349.8138794955,
           154, -3821779.853707643, -2093808.8053225805, 4641837.924190534,
           154, -3821779.853707643, -2093808.8053225805, 4641837.924190534,
           226, -5723826.264925561, -2669064.021283511, -889095.0157719625,
           236, -5669540.596844369, -2304083.4451725963, -1791032.530913303,
           240, -5510109.516997012, -2151995.3391535785, -2377273.4826697796
                ]

    }
}];

var czmlDataSource = new Cesium.CzmlDataSource();
czmlDataSource.load(builtInCzml, 'Sample CZML with 3D model');
viewer.dataSources.add(czmlDataSource);

2

What you’re looking for is a great arc interpolation algorithm. (see InterpolationAlgorithm interface: https://github.com/AnalyticalGraphicsInc/cesium/blob/master/Source/Core/InterpolationAlgorithm.js)

Unfortunately this does not currently exist in Cesium. You could do the subsampling on the client using PolylinePipeline.generateCartesianArc but you would still be increasing memory to store the sampled ephemeris.

3

Does this capability exist in cesium yet ?

1 Like
4

@alexvizgard

Does this sandcastle demo showcase what you are looking for?

This sandcastle uses a CZML data source and demonstrates how the path can be clamped to 3D Tiles.

-Sam

1 Like
5

Nice that looks good. My use case will be a submarine model that would be half submerged or fully submerged. Will the example you provided support this?

1 Like
6

@alexvizgard

Thank you, and yes! Please keep me in the loop - I would love to see the final result :smiley:

-Sam