# Is ClampToGround not supported for Billboards in CZML? **URL:** \ **Category:** CesiumJS\ **Created:** [August 5, 2018, 11:06pm UTC](https://community.cesium.com/t/is-clamptoground-not-supported-for-billboards-in-czml/7257 "2018-08-05T23:06:29Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![Jonathan\_Hall](https://avatars.discourse-cdn.com/v4/letter/j/7bcc69/32.png) [@Jonathan\_Hall](https://community.cesium.com/u/Jonathan_Hall)\ **Post date:** [August 5, 2018, 11:06pm UTC](https://community.cesium.com/t/is-clamptoground-not-supported-for-billboards-in-czml/7257/1 "2018-08-05T23:06:29Z")
**1. A concise explanation of the problem you’re experiencing.** Attempting to add “heightReference” : Cesium.HeightReference.CLAMP\_TO\_GROUND, to Billboard options in CZML, TypeError: Cannot read property ‘length’ of undefined the full error is TypeError: Cannot read property ‘length’ of undefined at processProperty (Cesium.js:137465) at processPacketData (Cesium.js:137603) at Array.processBillboard (Cesium.js:138107) at processCzmlPacket (Cesium.js:138685) at Function.CzmlDataSource.\_processCzml (Cesium.js:139063) at loadCzml (Cesium.js:138797) at Cesium.js:138778 at Promise.then (Cesium.js:1163) at when (Cesium.js:1026) at load (Cesium.js:138777) **2. A minimal code example. If you’ve found a bug, this helps us reproduce and repair it.** > **[Cesium Sandcastle](https://sandcastle.cesium.com/?src=CZML%20Billboard%20and%20Label.html&label=CZML)** > > The Cesium Sandcastle provides an interactive environment for testing Cesium code. insert on Line #11: “heightReference” : Cesium.HeightReference.CLAMP\_TO\_GROUND, **3. Context. Why do you need to do this? We might know a better way to accomplish your goal.** I am trying to animate a GPX tracklog using Billboard entities to represent the '“breadcrumb trail”. A better way night have been to include native support for GPX files in Cesium, if that project by Andre Nunes had ever been merged into master… then I wouldn’t struggle writing code to generate a CzmlDataSource from the GPX XML, which works great until I attempt to ClampToGround. **4. The Cesium version you’re using, your operating system and browser.** Cesium v1.4.8, Windows 7, Chrome ---
**Author:** ![Jonathan\_Hall](https://avatars.discourse-cdn.com/v4/letter/j/7bcc69/32.png) [@Jonathan\_Hall](https://community.cesium.com/u/Jonathan_Hall)\ **Post date:** [August 5, 2018, 11:48pm UTC](https://community.cesium.com/t/is-clamptoground-not-supported-for-billboards-in-czml/7257/2 "2018-08-05T23:48:52Z")
(NOT “heightReference”, which is usually the proper syntax) However, the billboard still disappears underground at certain times&places when the GPS Z elevation value is less than the Z value of Cesium World Terrain. Which leads me back to the original question, Is ClampToGround not supported for Billboards in CZML? The AGI logo graphic disappears underground in > **[Cesium Sandcastle](https://sandcastle.cesium.com/?src=CZML%20Billboard%20and%20Label.html&label=CZML)** > > The Cesium Sandcastle provides an interactive environment for testing Cesium code. when you paste the following line #11 “HeightReference”: Cesium.HeightReference.CLAMP\_TO\_GROUND, change to Cesium World Terrain in the Basemap Picker and zoom in on the AGI logo. Thanks- -Jon I solved the “TypeError: Cannot read property ‘length’ of undefined”, after reading [https://github.com/AnalyticalGraphicsInc/cesium/blob/1.48/Source/DataSources/CzmlDataSource.js](https://github.com/AnalyticalGraphicsInc/cesium/blob/1.48/Source/DataSources/CzmlDataSource.js) and realizing that in a CZML document, I **need to capitalize “HeightReference”** : Cesium.HeightReference.CLAMP\_TO\_GROUND, ---
**Author:** ![Scott\_Hunter](https://sea2.discourse-cdn.com/cesium/user_avatar/community.cesium.com/scott_hunter/32/2006_2.png) [@Scott\_Hunter](https://community.cesium.com/u/Scott_Hunter)\ **Post date:** [August 6, 2018, 12:58pm UTC](https://community.cesium.com/t/is-clamptoground-not-supported-for-billboards-in-czml/7257/3 "2018-08-06T12:58:55Z")
The correct syntax in CZML is: “heightReference”: “CLAMP\_TO\_GROUND” [sandcastle example](https://cesiumjs.org/Cesium/Build/Apps/Sandcastle/#c=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) The CZML property names for billboards are listed here: [https://github.com/AnalyticalGraphicsInc/czml-writer/wiki/Billboard](https://github.com/AnalyticalGraphicsInc/czml-writer/wiki/Billboard) and the string values for the HeightReference type are listed here: [https://github.com/AnalyticalGraphicsInc/czml-writer/wiki/HeightReferenceValue](https://github.com/AnalyticalGraphicsInc/czml-writer/wiki/HeightReferenceValue) ---
**Author:** ![Jonathan\_Hall](https://avatars.discourse-cdn.com/v4/letter/j/7bcc69/32.png) [@Jonathan\_Hall](https://community.cesium.com/u/Jonathan_Hall)\ **Post date:** [August 6, 2018, 1:08pm UTC](https://community.cesium.com/t/is-clamptoground-not-supported-for-billboards-in-czml/7257/4 "2018-08-06T13:08:57Z")
Thank you, Scott!