# Polygon's positions's height change after a time

**URL:** <https://community.cesium.com/t/polygons-positionss-height-change-after-a-time/15378>\
**Category:** CesiumJS\
**Created:** [September 22, 2021, 8:37am UTC](https://community.cesium.com/t/polygons-positionss-height-change-after-a-time/15378 "2021-09-22T08:37:25Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![zxc1987](https://sea2.discourse-cdn.com/cesium/user_avatar/community.cesium.com/zxc1987/32/4696_2.png) [@zxc1987](https://community.cesium.com/u/zxc1987)\
**Post date:** [September 22, 2021, 8:37am UTC](https://community.cesium.com/t/polygons-positionss-height-change-after-a-time/15378/1 "2021-09-22T08:37:25Z")

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I create a polygon clamped to terrain by setting perPositionHeight attribute to false  
and polygon’s hierarchy is a Cesium.CallbackProperty  
when 5 seconds later  
the polygon’s positions height changed to 0  
is this a bug?

> **[Cesium Sandcastle](https://sandcastle.cesium.com/#c=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)**
>
> The Cesium Sandcastle provides an interactive environment for testing Cesium code.

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<div class="post-metadata">

**Author:** ![sam.rothstein](https://sea2.discourse-cdn.com/cesium/user_avatar/community.cesium.com/sam.rothstein/32/6584_2.png) [@sam.rothstein](https://community.cesium.com/u/sam.rothstein)\
**Post date:** [September 27, 2021, 3:54am UTC](https://community.cesium.com/t/polygons-positionss-height-change-after-a-time/15378/2 "2021-09-27T03:54:32Z")

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@zxc1987

Thank you for bringing this to the community! From my understanding, this behavior seems reasonable. Given that you are clamping the polygon to the terrain, the height should match that of the terrain. This means that in some cases the height will be 0. Let me know if you have any other questions or concerns!

-Sam