Argon.js: Error: A frame state has not yet been received

Question

I am attempting to use argon.js server side so that I can convert lla coordinates to a predefined reference frame. I'm not rendering any graphics of course, I'm just using it to convert values. See SO question Using Geo-coordintes Instead of Cartesian to Draw in Argon and A-Frame for details.

Per that thread, I am trying to create a cesium entity for a fixed coordinate which I will later use to create other entities relative to it. When I do, everything runs until I get to the last line of the program var gtrefEntityPose = app.context.getEntityPose(gtrefEntity); where I receive Error: A frame state has not yet been received.

At first I thought this might be due to the setting the default reference entity to app.context.setDefaultReferenceFrame(app.context.localOriginEastUpSouth); since I did not have a local user yet due to it being server side. I looked up the documentation for setDefaultReferenceFrame as well as the possibility that I might need to use convertEntityReferenceFrame as well as the source code for each, but I am unable to make sense of it given my knowledge of the program.

I've put the error as well as my application code below.

Thanks for your help!

/home/path/to/folder/node_modules/@argonjs/argon/dist/argon.js:4323
    if (!cesium_imports_1.defined(this.serializedFrameState)) throw new Error(
                                                                ^
Error: A frame state has not yet been received
at ContextService.Object.defineProperty.get [as frame] (/home/path/to/folder/node_modules/@argonjs/argon/dist/argon.js:4323:89)
at ContextService.getTime (/home/path/to/folder/node_modules/@argonjs/argon/dist/argon.js:4343:32)
at ContextService.getEntityPose (/home/path/to/folder/node_modules/@argonjs/argon/dist/argon.js:4381:37)
at Object.<anonymous> (/home/path/to/folder/test.js:27:35)
at Module._compile (module.js:460:26)
at Object.Module._extensions..js (module.js:478:10)
at Module.load (module.js:355:32)
at Function.Module._load (module.js:310:12)
at Function.Module.runMain (module.js:501:10)
at startup (node.js:129:16)

Here is my code:

var Argon = require('@argonjs/argon');

var Cesium = Argon.Cesium;


var Cartesian3 = Cesium.Cartesian3;
var ConstantPositionProperty = Cesium.ConstantPositionProperty;
var ReferenceFrame = Cesium.ReferenceFrame;
var ReferenceEntity = Cesium.ReferenceEntity;
//var degToRad = THREE.Math.degToRad;

const app = Argon.init();
app.context.setDefaultReferenceFrame(app.context.localOriginEastUpSouth);

var data = { lla : { x : -84.398881, y : 33.778463, z : 276 }};

var gtref = Cartesian3.fromDegrees(data.lla.x, data.lla.y, data.lla.z);
var options = { position: new ConstantPositionProperty(gtref, ReferenceFrame.FIXED),
            orientation:  Cesium.Quaternion.IDENTITY
          };

var gtrefEntity = new Cesium.Entity(options);
var gtrefEntityPose = app.context.getEntityPose(gtrefEntity);

Answer 1

As it's currently designed, argon.js won't work server-side. In particular, the local coordinate frame is not set until argon.js has obtained a geospatial position and orientation for the "user", which is obtained either from Argon4 (if you are running in the Argon4 web browser) or from a combination of the web geolocation and deviceorientation API's (if you are running in a different browser).

With a full 6D pose (3D position + 3D orientation), the system does not know the position and viewing direction of the user, and cannot establish a local euclidean coordinate frame. Thus app.context.localOriginEastUpSouth remains undefined (the Cesium Entity exists, but it's position and orientation are not set), and app.context.getEntityPose(gtrefEntity) will fail.

To use argon.js server-side, you would need to modify it to allow the program to manually set the position and orientation of the viewer. I could imagine doing that, and even using it in a system that has the mobile client periodically sending the pose back to the server (via socket.io, for example). In situations where you don't care about the viewing direction (e.g., if you're just worrying about the position of the user) you could just set the orientation to identity and ignore the orientation in the returned pose.