# Ground Height Imagery Values Too Low

**URL:** <https://community.pix4d.com/t/ground-height-imagery-values-too-low/15362>\
**Category:** PIX4Dmapper\
**Created:** [November 6, 2020, 6:46pm UTC](https://community.pix4d.com/t/ground-height-imagery-values-too-low/15362 "2020-11-06T18:46:49Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![ftalton](https://avatars.discourse-cdn.com/v4/letter/f/7bcc69/32.png) [@ftalton](https://community.pix4d.com/u/ftalton)\
**Post date:** [November 6, 2020, 6:46pm UTC](https://community.pix4d.com/t/ground-height-imagery-values-too-low/15362/1 "2020-11-06T18:46:49Z")

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Hello!

We are modelling tree canopy using a DJI Phantom that was flown with an active RTK. The area that we are flying has an elevation (terrain / bare earth) of between 71-77m AMSL.

The photogrammetry in Pix4D Mapper is showing values that comprise the ground are 43m, so substantially below what the known elevation of the area is. Those values are not anomalous, they are representative of the ground at large. Does anyone have any idea what might be the issue here?

Thanks!

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**Author:** ![joan.cano](https://sea2.discourse-cdn.com/pix4d/user_avatar/community.pix4d.com/joan.cano/32/1886_2.png) [@joan.cano](https://community.pix4d.com/u/joan.cano)\
**Post date:** [November 7, 2020, 9:41pm UTC](https://community.pix4d.com/t/ground-height-imagery-values-too-low/15362/2 "2020-11-07T21:41:04Z")

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Hi,  
even if your PH4 it’s flying with the RTK activated, the geometadata of your pictures it’s WGS84 (vertical altitude too).

Try to apply the geoid of your area or use some GCP taken with a GPS 🙂

- [How to define Pix4D outputs with respect to a Geoid model](https://support.pix4d.com/hc/en-us/articles/360021076212-How-to-define-Pix4D-outputs-with-respect-to-a-Geoid-model)

- [Accurate georeferencing in Pix4D - Pix4Dmapper Video Tutorial 2 - YouTube](https://www.youtube.com/watch?v=DxiO4DZHtNA&list=PL8ZbncaV3f_anQs_DoyKUxmNDApxM0HT8&index=2)

Regards,  
Joan

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**Author:** ![ftalton](https://avatars.discourse-cdn.com/v4/letter/f/7bcc69/32.png) [@ftalton](https://community.pix4d.com/u/ftalton)\
**Post date:** [November 12, 2020, 7:09pm UTC](https://community.pix4d.com/t/ground-height-imagery-values-too-low/15362/3 "2020-11-12T19:09:04Z")

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Thank you Joan.

We flew 1 flight at 90deg and 1 flight at 30deg, and the imagery from the 30deg seems to be rendering the height correctly. No matter what I do to the 90deg, or a combination of the 90deg + 30deg imagery, it still gives me elevation values of 44m range, instead of the correct 70-80m range.

Would it be helpful to see the Quality Report from the one that rendered correctly?

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**Author:** ![joan.cano](https://sea2.discourse-cdn.com/pix4d/user_avatar/community.pix4d.com/joan.cano/32/1886_2.png) [@joan.cano](https://community.pix4d.com/u/joan.cano)\
**Post date:** [November 14, 2020, 7:17pm UTC](https://community.pix4d.com/t/ground-height-imagery-values-too-low/15362/4 "2020-11-14T19:17:15Z")

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Yes, could you share?