Cesium 3d tiles格式介绍

这是一个3d tiles的格式文件

{
"asset": {
"version" : "0.0"
}, //Asset是一个包含了整体tileset元数据属性的对象。其中version属性是定义3D Tiles版本的字符串。版本号定义了tileset.json的JSON格式和瓦片格式的基础设定。tilesetVersion属性是一个选填的字符串，用于定义特定应用中tileset的版本，可以用于更新tileset。
"properties": {
"Longitude": {
"minimum": -0.0005589940528287436,
"maximum": 0.0001096066770252439
},
"Latitude": {
"minimum": 0.8987242766850329,
"maximum": 0.899060112939701
},
"Height": {
"minimum": 1,
"maximum": 241.6
}
}, //Properties是一个包含tileset中每个要素每个属性信息的对象。这个tileset.json代码片段是用于三维建筑，每一个瓦片都有建筑物模型，每个模型都有Height属性
"geometricError": 494.50961650991815,//是一个非负数值，在tileset没有渲染时定义米制误差
"root": {  //root用于定义根瓦片（参考上一节）。root.geometricError与最高层级tileset.json的geometricError不同。tileset.json的geometricError定义的误差用在整个tileset还没有被渲染的时候；root.geometricError定义的误差用在只有根瓦片被渲染的时候。

"boundingVolume": {
"region": [
-0.0005682966577418737,
0.8987233516605286,
0.00011646582098558159,
0.8990603398325034,
0,
241.6
]
},
"content": {
"boundingVolume": {
"region": [
-0.0004001690908972599,
0.8988700116775743,
0.00010096729722787196,
0.8989625664878067,
0,
241.6
]
},
"url": "0/0/0.b3dm"
},
"geometricError": 268.37878244706053,
"refine": "ADD",
"children": [ //是定义子瓦片对象的数组。每个子瓦片都有boundingVolume，这个边界体被父瓦片的boundingVolume完全包围，通常子瓦片的 geometricError要小于父瓦片的geometricError。对于叶子瓦片而言，子瓦片数组的长度为0，
{
"boundingVolume": {
"region": [
-0.0004853062518095434,
0.898741188925484,
-0.0002736676267127107,
0.8989037314387226,
0,
158.4
]
},
"content": {
"boundingVolume": {
"region": [
-0.0004058588642587614,
0.898746512179703,
-0.0002736676267127107,
0.8989037314387226,
0,
158.4
]
},
"url": "1/0/0.b3dm"
},
"geometricError": 159.43385994848,
"children": [
{
"boundingVolume": {
"region": [
-0.0004853062518095434,
0.898741188925484,
-0.0003930656008416433,
0.898818995703538,
0,
66.7
]
},
"content": {
"url": "2/0/0.b3dm"
},
"geometricError": 10.831613588830955
},
{
"boundingVolume": {
"region": [
-0.0003984063083527456,
0.8987434753068045,
-0.00028070130359824817,
0.8988027117816164,
0,
48.2
]
},
"content": {
"url": "2/1/0.b3dm"
},
"geometricError": 11.833855250694043
},
{
"boundingVolume": {
"region": [
-0.00039631191325035245,
0.8988008442793176,
-0.000280491864088009,
0.8989002407802179,
0,
78.1
]
},
"content": {
"url": "2/1/1.b3dm"
},
"geometricError": 24.187299340965403
},
{
"boundingVolume": {
"region": [
-0.00047979101137324135,
0.8988092742196048,
-0.0003937113726648811,
0.898901462510695,
0,
122.2
]
},
"content": {
"url": "2/0/1.b3dm"
},
"geometricError": 48.508446081365975
}
]
},
{
"boundingVolume": {
"region": [
-0.0002874033679259065,
0.8987233516605286,
0.00009827949017980081,
0.8988939226883266,
0,
75.2
]
},
"content": {
"boundingVolume": {
"region": [
-0.00028230700651008276,
0.8987309438427749,
-0.00011402236003278958,
0.8988939226883266,
0,
75.2
]
},
"url": "1/1/0.b3dm"
},
"geometricError": 132.82048511777703,
"children": [
{
"boundingVolume": {
"region": [
-0.0002874033679259065,
0.8987293381398633,
-0.00018024015185345448,
0.8987995352823785,
0,
38.1
]
},
"content": {
"url": "2/2/0.b3dm"
},
"geometricError": 4.206139430532202
},
{
"boundingVolume": {
"region": [
-0.00018407987620784196,
0.8987233516605286,
-0.0000894132175796695,
0.8987836876927705,
0,
72.9
]
},
"content": {
"url": "2/3/0.b3dm"
},
"geometricError": 0
},
{
"boundingVolume": {
"region": [
-0.00018493508754131914,
0.8987896218122265,
0.00009827949017980081,
0.8988920377327339,
0,
46.9
]
},
"content": {
"url": "2/3/1.b3dm"
},
"geometricError": 0
},
{
"boundingVolume": {
"region": [
-0.00027722809838677943,
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-0.00017832028967626075,
0.8988916014004213,
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55.4
]
},
"content": {
"url": "2/2/1.b3dm"
},
"geometricError": 0
}
]
},
{
"boundingVolume": {
"region": [
-0.0002821848334624433,
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0.00011646582098558159,
0.8990603398325034,
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158
]
},
"content": {
"boundingVolume": {
"region": [
-0.0002782229360604159,
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0.899046220118855,
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158
]
},
"url": "1/1/1.b3dm"
},
"geometricError": 156.46285780389445,
"children": [
{
"boundingVolume": {
"region": [
-0.00027865926837341453,
0.8988880758353316,
-0.00014501940754820897,
0.8989746092596459,
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77.3
]
},
"content": {
"url": "2/2/2.b3dm"
},
"geometricError": 0
},
{
"boundingVolume": {
"region": [
-0.00015598007525073333,
0.8988867144785156,
0.00011646582098558159,
0.8989826028676196,
0,
106.2
]
},
"content": {
"url": "2/3/2.b3dm"
},
"geometricError": 0
},
{
"boundingVolume": {
"region": [
-0.00015252432333178438,
0.8989769130942584,
0.00003328342883553189,
0.8990603398325034,
0,
67.9
]
},
"content": {
"url": "2/3/3.b3dm"
},
"geometricError": 8.010233984367021
},
{
"boundingVolume": {
"region": [
-0.0002821848334624433,
0.8989765465751156,
-0.0001477072145962801,
0.899040914317929,
0,
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]
},
"content": {
"url": "2/2/3.b3dm"
},
"geometricError": 40.38435697163592
}
]
},
{
"boundingVolume": {
"region": [
-0.0005682966577418737,
0.8989007643789939,
-0.0002669481090925327,
0.8990582279841088,
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]
},
"content": {
"boundingVolume": {
"region": [
-0.0005526410543514849,
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-0.0002669481090925327,
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]
},
"url": "1/0/1.b3dm"
},
"geometricError": 149.600454457028,
"children": [
{
"boundingVolume": {
"region": [
-0.0005474399731805417,
0.8989017068567899,
-0.00040917498983755046,
0.8990014698768336,
0,
81.2
]
},
"content": {
"url": "2/0/2.b3dm"
},
"geometricError": 0
},
{
"boundingVolume": {
"region": [
-0.00041203732981082115,
0.8989007643789939,
-0.00027176521782803744,
0.8989922894449685,
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108.7
]
},
"content": {
"url": "2/1/2.b3dm"
},
"geometricError": 0
},
{
"boundingVolume": {
"region": [
-0.0004253716452960582,
0.8989891478523147,
-0.0002760587277879431,
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30.1
]
},
"content": {
"url": "2/1/3.b3dm"
},
"geometricError": 18.837170280352364
},
{
"boundingVolume": {
"region": [
-0.0005682966577418737,
0.8989984853638134,
-0.000407220221075317,
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53.3
]
},
"content": {
"url": "2/0/3.b3dm"
},
"geometricError": 67.4774528507299
}
]
}
]
}
}

Tileset.json中最高层级的对象有四个属性：asset, properties, geometricError,

和 root。

Asset是一个包含了整体tileset元数据属性的对象。其中version属性是定义3D Tiles版本的字符串。版本号定义了tileset.json的JSON格式和瓦片格式的基础设定。tilesetVersion属性是一个选填的字符串，用于定义特定应用中tileset的版本，可以用于更新tileset。

Properties是一个包含tileset中每个要素每个属性信息的对象。这个tileset.json代码片段是用于三维建筑，每一个瓦片都有建筑物模型，每个模型都有Height属性（参考Batched 3D Model瓦片格式中的Batch Table）。

properties 每个对象的名称都与每个要素中对应属性的名称相同，定义了他们的minimum 和 maximum数值，在自定义色阶样式时很有用。

geometricError是一个非负数值，在tileset没有渲染时定义米制误差。

root用于定义根瓦片（参考上一节）。root.geometricError与最高层级tileset.json的geometricError不同。tileset.json的geometricError定义的误差用在整个tileset还没有被渲染的时候；root.geometricError定义的误差用在只有根瓦片被渲染的时候。

root.children是定义子瓦片对象的数组。每个子瓦片都有boundingVolume，这个边界体被父瓦片的boundingVolume完全包围，通常子瓦片的 geometricError要小于父瓦片的geometricError。对于叶子瓦片而言，子瓦片数组的长度为0，

所以 children也可以不定义。