# vertical shift between point cloud and DSM data

**URL:** <https://community.pix4d.com/t/vertical-shift-between-point-cloud-and-dsm-data/7454>\
**Category:** PIX4Dmapper Questions/Troubleshooting\
**Created:** [October 30, 2018, 8:25pm UTC](https://community.pix4d.com/t/vertical-shift-between-point-cloud-and-dsm-data/7454 "2018-10-30T20:25:11Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![Tony\_Ottawa](https://avatars.discourse-cdn.com/v4/letter/t/a4c791/32.png) [@Tony\_Ottawa](https://community.pix4d.com/u/Tony_Ottawa)\
**Post date:** [October 30, 2018, 8:25pm UTC](https://community.pix4d.com/t/vertical-shift-between-point-cloud-and-dsm-data/7454/1 "2018-10-30T20:25:11Z")

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I’m confirming the accuracy of using UAS and Pix4DMapper for our road projects in anticipation of using aerial photography for our hard surface mapping.&nbsp; I was able to successfully create a point cloud and the necessary files to import a DSM into Civil 3D.&nbsp; At first I wasn’t too pleased with my results.&nbsp; I used 21 GCP’s over a 1.5 mile project and had them located with RTK GPS.&nbsp; I selected the proper state plane coordinates for my output files however; when I imported the “dsm\_100cm.xyz” over a project which was completed with total station, I found that my elevation was a consistent 0.40’ off.&nbsp; But, if I reviewed the coordinate in the rayCLoud editor they are right on!&nbsp; If I applied a manual -0.40’ to the dsm in civil3D everything matched great!&nbsp; I was surprised to see my data within a 0.07’ of our total station locations.&nbsp; This is an amazing result, but I’m concerned about why I had to apply a manual shift.

My question is:&nbsp; How come in the rayCLoud editor my elevations are perfect, but yet when I import the dsm surface into CIvil3D those same elevations are shifted 0.40’? &nbsp;&nbsp;

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**Author:** ![Tony\_Ottawa](https://avatars.discourse-cdn.com/v4/letter/t/a4c791/32.png) [@Tony\_Ottawa](https://community.pix4d.com/u/Tony_Ottawa)\
**Post date:** [November 1, 2018, 7:50pm UTC](https://community.pix4d.com/t/vertical-shift-between-point-cloud-and-dsm-data/7454/2 "2018-11-01T19:50:41Z")

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UPDATE:&nbsp; after further review the vertical error was found to be in an unadjusted GPS pole by the surveyor.&nbsp; All of his GPS locations on the GCP’s were 0.24’ higher than actual.&nbsp; This brings the results into range depicted on the error report in Pix4D.

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**Author:** ![Daniel\_Rico\_Cordero](https://sea2.discourse-cdn.com/pix4d/user_avatar/community.pix4d.com/daniel_rico_cordero/32/187_2.png) [@Daniel\_Rico\_Cordero](https://community.pix4d.com/u/Daniel_Rico_Cordero)\
**Post date:** [November 2, 2018, 4:02pm UTC](https://community.pix4d.com/t/vertical-shift-between-point-cloud-and-dsm-data/7454/3 "2018-11-02T16:02:01Z")

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Hello Tony,

Thank you for the update.

Good to know that you got the expected results.

I think you can find useful this [blog post](https://www.pix4d.com/blog/rtk-ppk-drones-gcp-comparison). It compares&nbsp;the accuracy obtained with GCPs and RTK/PPK geotags.

In a few days, there will be a new one analyzing&nbsp;the accuracy of the point cloud depending on the GCP distribution which could be of your interest too.

Regards.

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**Author:** ![Daniel\_Rico\_Cordero](https://sea2.discourse-cdn.com/pix4d/user_avatar/community.pix4d.com/daniel_rico_cordero/32/187_2.png) [@Daniel\_Rico\_Cordero](https://community.pix4d.com/u/Daniel_Rico_Cordero)\
**Post date:** [November 5, 2018, 8:19am UTC](https://community.pix4d.com/t/vertical-shift-between-point-cloud-and-dsm-data/7454/4 "2018-11-05T08:19:51Z")

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Hi again,

This is the blog post I was talking about in my previous post:

[Do more GCPs equal more accurate drone maps?](https://www.pix4d.com/blog/GCP-accuracy-drone-maps)

Regards.

&nbsp;