# heightReference for position in CZML **URL:** \ **Category:** CesiumJS\ **Created:** [July 25, 2017, 3:00pm UTC](https://community.cesium.com/t/heightreference-for-position-in-czml/5853 "2017-07-25T15:00:09Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![bf1](https://avatars.discourse-cdn.com/v4/letter/b/e0b2c6/32.png) [@bf1](https://community.cesium.com/u/bf1)\ **Post date:** [July 25, 2017, 3:00pm UTC](https://community.cesium.com/t/heightreference-for-position-in-czml/5853/1 "2017-07-25T15:00:09Z")
Hi all, I have converted a GPX track to CZML. I have the path rendering properly but am unable to get the path to clamp to ground--it's roughly 30m below the surface but varying over time--probably because the GPS was changing its height fix over time. I attempted to resolve this by scrubbing the heights through a sampleTerrain function, which resulted in slightly different values, but still roughly 30m below the surface. Is there a way to tell a position -\> cartographicDegrees to clamp itself to the terrain? Thanks, Ben ---
**Author:** ![Gabby\_Getz](https://sea2.discourse-cdn.com/cesium/user_avatar/community.cesium.com/gabby_getz/32/7838_2.png) [@Gabby\_Getz](https://community.cesium.com/u/Gabby_Getz)\ **Post date:** [July 27, 2017, 7:11pm UTC](https://community.cesium.com/t/heightreference-for-position-in-czml/5853/2 "2017-07-27T19:11:28Z")
Hi Ben, I think you can use the CZML property [HeighReference](https://github.com/AnalyticalGraphicsInc/czml-writer/wiki/HeightReference) with the value CLAMP\_TO\_GROUND `` Thanks, Gabby ---
**Author:** ![bf1](https://avatars.discourse-cdn.com/v4/letter/b/e0b2c6/32.png) [@bf1](https://community.cesium.com/u/bf1)\ **Post date:** [July 29, 2017, 4:35pm UTC](https://community.cesium.com/t/heightreference-for-position-in-czml/5853/3 "2017-07-29T16:35:01Z")
Thanks for the suggestion. I've given that a shot. Appears to have no effect. "position": {     "interpolationAlgorithm": "LAGRANGE",     "interpolationDegree": 1,     "epoch": "2017-06-05T16:49:14Z",     "heightReference" : "CLAMP\_TO\_GROUND",     "cartographicDegrees": [       0,       -106.957785124,       31.9563742261,       1218.13, ---
**Author:** ![Gabby\_Getz](https://sea2.discourse-cdn.com/cesium/user_avatar/community.cesium.com/gabby_getz/32/7838_2.png) [@Gabby\_Getz](https://community.cesium.com/u/Gabby_Getz)\ **Post date:** [August 1, 2017, 2:25pm UTC](https://community.cesium.com/t/heightreference-for-position-in-czml/5853/4 "2017-08-01T14:25:31Z")
Sorry I don’t have a czml example, but here’s the sandcastle demo for clamping to ground: [http://cesiumjs.org/Cesium/Apps/Sandcastle/index.html?src=Ground%20Clamping.html&label=Showcases](http://cesiumjs.org/Cesium/Apps/Sandcastle/index.html?src=Ground%20Clamping.html&label=Showcases), maybe the “Sample line positions” example is relevant? ---
**Author:** ![bf1](https://avatars.discourse-cdn.com/v4/letter/b/e0b2c6/32.png) [@bf1](https://community.cesium.com/u/bf1)\ **Post date:** [August 4, 2017, 7:52pm UTC](https://community.cesium.com/t/heightreference-for-position-in-czml/5853/5 "2017-08-04T19:52:59Z")
Thank you for this help. My code to reset the heights of the path points wasn't using sampleTerrainMostDetailed. Now it is, and it's working like a charm. I really appreciate the help. ---
**Author:** ![Gabby\_Getz](https://sea2.discourse-cdn.com/cesium/user_avatar/community.cesium.com/gabby_getz/32/7838_2.png) [@Gabby\_Getz](https://community.cesium.com/u/Gabby_Getz)\ **Post date:** [August 7, 2017, 1:34pm UTC](https://community.cesium.com/t/heightreference-for-position-in-czml/5853/6 "2017-08-07T13:34:42Z")
Great! I’m glad to hear its working!