BCE dates?

CesiumJS
1

As far as I can tell, there is no way to put BCE or negative dates into the Cesium timeline. The clock will scrub backwards into BCE but if I try pulling the timeline back that far, it will crash the page and give me an invalid iso8601 error:

DeveloperError: Invalid ISO 8601 date.
Error
    at new t (http://localhost:8080/Build/Cesium/Cesium.js:417:6242)
    at Function.M.fromIso8601 (http://localhost:8080/Build/Cesium/Cesium.js:423:5193)
    at w._makeTics (http://localhost:8080/Build/Cesium/Cesium.js:464:12615)
    at w.zoomTo (http://localhost:8080/Build/Cesium/Cesium.js:464:10898)
    at w.updateFromClock (http://localhost:8080/Build/Cesium/Cesium.js:464:15527)
    at r.raiseEvent (http://localhost:8080/Build/Cesium/Cesium.js:417:22698)
    at l.tick (http://localhost:8080/Build/Cesium/Cesium.js:423:12017)
    at P.render (http://localhost:8080/Build/Cesium/Cesium.js:462:15594)
    at t (http://localhost:8080/Build/Cesium/Cesium.js:462:2645)

Are there any work arounds?

2

This looks like a bug in the _makTics function around line 379. Cesium internally uses JulianDate, which can go back to 4713 BCE but standard ISO8601 dates can not represent times before 0 BCE. The few lines of code I linked to should use JulianDate.toGregorianDate instead of creating an ISO8601 string. If you want to update the code, we’ll gladly take a pull request, I think it should be pretty straight forward.

If you need dates before 4713 BCE, I think it will still work, I’m not sure if there are any ramifications to negative Julian Day numbers in our code.

3

Thanks! I'm not sure this is a full fix because it's not splitting up the durations like the current function is doing but it works for my purposes. I went to line 379 and inserted:

if(startJulian.dayNumber<1721423.5){
         epochJulian = startJulian;
        }
        else if (duration > 315360000)...

1721423.5 is the first AD Julian Day Number so everything before that just sets epochJulian to startJulian.

Again, not ideal but it works for my purposes. I've never contributed to a large open source project before but let me know if this is worth submitting a pull request for. It'd be great if the next version of Cesium is able to deal with BCE dates out of the box.

Thanks so much for your help!

4

It never hurts to submit a pull-request when you fix a bug and/or edge-case. It’s what makes open-source work :slight_smile:

Just make sure to give a quick read of the contributing guide before creating your first pull-request to make sure it is good to go when the team reviews it.