# Vertical Inacuracy

**URL:** <https://community.pix4d.com/t/vertical-inacuracy/8413>\
**Category:** PIX4Dmapper Questions/Troubleshooting\
**Created:** [May 30, 2019, 8:19am UTC](https://community.pix4d.com/t/vertical-inacuracy/8413 "2019-05-30T08:19:28Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![Malcolm\_Duncan](https://avatars.discourse-cdn.com/v4/letter/m/e5b9ba/32.png) [@Malcolm\_Duncan](https://community.pix4d.com/u/Malcolm_Duncan)\
**Post date:** [May 30, 2019, 8:19am UTC](https://community.pix4d.com/t/vertical-inacuracy/8413/1 "2019-05-30T08:19:28Z")

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Hi

I have image geolocation with WGS84, Coord System WGS84 (EGM96 Geoid).

GCPs obtained by GNSS and transformed to OSGB36(15) using Vertical coordinate Height above Ordnance Datum, Newlyn UK (ODN), therefore local geoid model **but** in GCP Manager & Output coordinates the EGM96 true Geoid is specified, which contradicts the ODN local geoid model.

Consequently, in the Quality Report there is an approx. vertical variance in Z of -78m (minus 78m)

After Stage 1 Processing the rayCloud looks like

Can you advise on how I adjust to ODN please?

Malcolm (University of Bolton (UK)

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**Author:** ![Blaz](https://sea2.discourse-cdn.com/pix4d/user_avatar/community.pix4d.com/blaz/32/4344_2.png) [@Blaz](https://community.pix4d.com/u/Blaz)\
**Post date:** [June 3, 2019, 9:28am UTC](https://community.pix4d.com/t/vertical-inacuracy/8413/2 "2019-06-03T09:28:55Z")

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Hi Malcon,

could you please share the quality report with us? You can upload it [here](https://pix4d365-my.sharepoint.com/:f:/g/personal/blaz_vidmar_pix4d_com/EgT8g-q_U5VFmtTpuvvDw7cB4xcIJcg-cAKCzWq7V70O9w?e=51a3tM).&nbsp;

Are you using an RTK drone or a standard precision drone?

Best,

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**Author:** ![Malcolm\_Duncan](https://avatars.discourse-cdn.com/v4/letter/m/e5b9ba/32.png) [@Malcolm\_Duncan](https://community.pix4d.com/u/Malcolm_Duncan)\
**Post date:** [June 3, 2019, 12:20pm UTC](https://community.pix4d.com/t/vertical-inacuracy/8413/3 "2019-06-03T12:20:43Z")

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Hi Blaz

I am using a standard precision Inspire 2 with a Zemuse X5s RGB Camera. The BS Scout Hut Report has been uploaded

Regards

Malcolm

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<div class="post-metadata">

**Author:** ![Blaz](https://sea2.discourse-cdn.com/pix4d/user_avatar/community.pix4d.com/blaz/32/4344_2.png) [@Blaz](https://community.pix4d.com/u/Blaz)\
**Post date:** [June 3, 2019, 2:38pm UTC](https://community.pix4d.com/t/vertical-inacuracy/8413/4 "2019-06-03T14:38:59Z")

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Thank you for the additional information.&nbsp;

The offset in this project can be due to different reasons:

1. The image geotags are inaccurate. In most cases, **this is related to DJI drones** where the vertical coordinate can be off by several meters and can reach an error of 100 meters. Note that this is just an offset meaning that within the model, the accuracy is not affected, only the absolute location is.

- Follow the instructions in the support article to&nbsp;[shift the point cloud to align with the GCP initial position](https://support.pix4d.com/hc/en-us/articles/206544136-Vertical-shift-between-the-model-and-the-GCPs-Cannot-mark-the-GCPs-in-the-rayCloud).

1. Wrong vertical coordinate systems selected.&nbsp;

- Ensure that the vertical coordinate system for both the&nbsp;[Image coordinate system](https://support.pix4d.com/hc/en-us/articles/203755985-How-to-verify-that-the-Image-Geolocation-and-the-Image-Coordinate-System-are-Correct)&nbsp;and the&nbsp;[GCP coordinate system](https://support.pix4d.com/hc/en-us/articles/202557749-Menu-Project-GCP-MTP-Manager-GCP-Coordinate-System)&nbsp;is correct. If the heights are based on a vertical reference frame that is not included in Pix4D, then the&nbsp;[Geoid Height Above the Ellipsoid](https://support.pix4d.com/hc/en-us/articles/211739726) function can be used.&nbsp;

In both cases, if GCPs are used, the project will be corrected and fitted to the position of the GCPs.&nbsp;

Best,

&nbsp;