CZMLDataSource with custom ellipsoids

[malaretv]

CZMLDataSource has a number of spots where Ellipsoid.WGS84 is assumed and it makes the datasource unusable for non-earth maps.

One example is here where Ellipsoid.WGS84 is explicitly called

cesium/packages/engine/Source/DataSources/CzmlDataSource.js

Lines 275 to 286 in 4244bc0

	function convertCartographicRadiansToCartesian(cartographicRadians) {
	const length = cartographicRadians.length;
	if (length === 3) {
	scratchCartographic.longitude = cartographicRadians[0];
	scratchCartographic.latitude = cartographicRadians[1];
	scratchCartographic.height = cartographicRadians[2];
	Ellipsoid.WGS84.cartographicToCartesian(
	scratchCartographic,
	scratchCartesian
	);
	return [scratchCartesian.x, scratchCartesian.y, scratchCartesian.z];
	}

And also like here where the absence of an ellipsoid parameter to Cartesian3.fromDegreesArrayHeights() causes WGS84 to be assumed internally.

cesium/packages/engine/Source/DataSources/CzmlDataSource.js

Lines 1828 to 1830 in 4244bc0

	packetData.array = Cartesian3.fromDegreesArrayHeights(
	packetData.cartographicDegrees
	);

I am happy to provide a fix for this but was wondering what the team thinks is the best path to add this option?

I could add an ellipsoid to be passed in with the LoadOptions with each new CZMLDataSource() call. e.g.

let datasource = new CZMLDataSource(url, {ellipsoid: myCustomEllipsoid})

This seems nicest in terms of API but implementation-wise would mean passing the ellipsoid value through all the individual nested process*() calls.

The other option is the default ellipsoid could exist as a static property on CZMLDataSource. All internal places an ellipsoid is required would use this static property. The user code to then use a different ellipsoid could be something like this:

CZMLDataSource.DEFAULT_ELLIPSOID = myCustomEllipsoid;
let datasource = new CZMLDataSource(url)

Much simpler to implement but not great if multiple ellipsoid values are desired within an application -- I imagine that case is pretty rare?

thoughts?

[ggetz]

Hi @malaretv, thanks for bringing up this issue! I think this has been discussed previously and the conclusion mentioned at the time to use a default ellipsoid. Since this is so similar, I'll close this issue now to keep the discussion in one place. If you have any further input on this, please post it there instead.

As a workaround in the meantime, it should be possible to modify WGS84 to be a custom ellipsoid.

Thanks!