time-dependent draped polygon boundaries

CesiumJS
1

Hi there,

first off awesome work on the Cesium project, it looks really great from my limited experience so far.

I am trying to visualise a polygon that changes over time, and needs to be draped over the terrain.

I have managed to get a single polygon to 'pseudo' drape by using the Cesium.sampleTerrain() function for each of the vertices, which works fine when i create the polygon myself in javascript using the Cesium.GeometryInstance() and adding it to the scene.primitives, but i can't find any examples of adding the time intervals to the geometry for changing the poly with the time slider.

Further, using CZML i can show the polys changing over time by putting the appropriate interval value in the show attribute, but then i lose the ability to use sampleTerrain() to redefine the heights, and even if i iterate over the vertices added by the CZML, i cannot seem to apply the perPositionHeight: true attribute which is necessary.

2

to respond to myself a bit:

i have finally managed to get time-dependent, draped polys but i'm not super happy with how i did it.

i found in the source (unminified:vb23 Cesium.js:38999 )in PolygonGeometry.createGeometry() that if i hardcode var perPositionHeight = true; then my dynamic (both CZML and DynamicObject()) features all respect their vertices' z coords. I don't have a problem having this set to true coz i cant think of a reason why i would ever want z coords ignored (?).

so now i can use CZML to make pseudo-draped, dynamic polys, assuming i loop over the polys found in the CZML and update their z coords using sampleTerrain().

if there is a better way to define perPositionHeight for dynamic polygons then i'd be happy to hear it.. or maybe this will be addressed with vectors conforming to terrain that i see in the product roadmap.

have a good weekend,

-i