gltf model load error

[leation]

test gltf model:https://github.com/leation/mydata/blob/master/Bee.glb.

Cesium.js:254066 An error occurred while rendering. Rendering has stopped.
undefined
TypeError: Cannot read property 'parents' of undefined
TypeError: Cannot read property 'parents' of undefined
at createRuntimeNodes (http://localhost:8888/test/cesium/Cesium.js:153548:33)
at createResources (http://localhost:8888/test/cesium/Cesium.js:153704:9)
at Model.update (http://localhost:8888/test/cesium/Cesium.js:154606:21)
at PrimitiveCollection.update (http://localhost:8888/test/cesium/Cesium.js:135195:27)
at updateAndRenderPrimitives (http://localhost:8888/test/cesium/Cesium.js:242236:27)
at executeCommandsInViewport (http://localhost:8888/test/cesium/Cesium.js:242075:13)
at updateAndExecuteCommands (http://localhost:8888/test/cesium/Cesium.js:241883:13)
at render (http://localhost:8888/test/cesium/Cesium.js:242534:9)
at tryAndCatchError (http://localhost:8888/test/cesium/Cesium.js:242554:13)
at Scene.render (http://localhost:8888/test/cesium/Cesium.js:242622:13)

[mramato]

@leation thanks for the bug report!

https://gltf-viewer.donmccurdy.com/ loads this model without any issues so I can't think of a good reason Cesium shouldn't load it either. However it looks like there are some errors in it, you can see these by dragging/dropping it into the glTF Validator here: http://github.khronos.org/glTF-Validator/

@lilleyse or @likangning93 anything obvious going on here? Perhaps this is a trivial fix?

[emackey]

The Bee model fails validation due to duplicate keyframes on the last animation time.

Looks like Unity fails to load the model in KhronosGroup/UnityGLTF#476 with a slightly more helpful error message:

Unity does not allow you to put two keyframes in with the same time

Perhaps there's a newer version of the Bee model where this was fixed in the glTF file?

[leation]

Thank you very much.

[leation]

@mramato,@emackey,when I use https://gltf-viewer.donmccurdy.com/ to load the Bee.glb,I found it's has three animations,is this the reason that Cesium can't load Bee.glb？

[emackey]

No, the 3 animations are not the problem. See in the lower-left where the red box says 642 errors in the file? That's the problem.

Digging into those error messages yesterday, I had found that there are many moving parts on the bee, and each part in each of the 3 animations has a duplicate animation frame on the end. Specifically, the last and second-to-last keyframes appear at the exact same time, which is illegal in glTF. Three and Babylon don't choke on it, but Cesium and Unity do, and as you can see the glTF Validator also fails the file.

It looks like this file was exported by an older Microsoft glTF writer, and I vaguely remember there may have been a bug fixed some time ago related to duplicated keyframes at the ends of animations. Where did you get this file? Can you export a new copy with a newer version of the exporter?

[leation]

@emackey thanks for your detailed explanation.This Bee.glb file is one demo model file of the windows10 3d viewer .As you explained,probably,the Bee.glb file's format is not rigorous.

[leation]

@emackey thanks very much. just I try to use gltf-import-export to convert the Bee.glb to gltf file,the command is: gltf-import-export Bee.glb -o Bee.gltf.Then I use Cesium to load this Bee.gltf,happily,it's works,maybe gltf-import-export can solver error of the Bee.glb.but if I try to use blender to convert glb file to gltf file,it's not work,mayby blender has same bug.

[emackey]

Glad you got it working.

It occurred to me that I was reacting to the validation failures, but I didn't actually stop to trap Cesium's actual problem in the debugger. Turns out the two are not the same.

It looks like Cesium is having trouble with the model's skeleton, and this issue may be related to (or possibly duplicate with) issue #8175.

[Lemonjay]

@emackey thanks very much. just I try to use gltf-import-export to convert the Bee.glb to gltf file,the command is: gltf-import-export Bee.glb -o Bee.gltf.Then I use Cesium to load this Bee.gltf,happily,it's works,maybe gltf-import-export can solver error of the Bee.glb.but if I try to use blender to convert glb file to gltf file,it's not work,mayby blender has same bug.

I tried,it‘s not work

[emackey]

Although this issue is closed, the Bee is still marked as a bug (no pun intended!) in issue #8759.

I believe what's happening is that Cesium is computing a bounding sphere around the original mesh, and not accounting for the skin deformations of the mesh. That's paired with another artifact of the model scale: small models are sometimes built to "centimeter" scale, where a scaling factor of 0.01 is applied to the whole model. But scaling doesn't affect skinned meshes directly, it affects them by scaling the skeleton instead, which the bounding sphere is not aware of.

So the bee's mesh, with skinning applied to it, is scaled down to 1/100th of its former size. The camera is then placed 100 times further away from the bee than it should be, and kept away.

I believe the correct answer is that the bounding sphere needs to somehow account for sizing applied by skinning.