# Quality Check on GCPs - GCPs are used and the GCP error is more than 4 times the average GSD

**URL:** <https://community.pix4d.com/t/quality-check-on-gcps-gcps-are-used-and-the-gcp-error-is-more-than-4-times-the-average-gsd/23361>\
**Category:** PIX4Dmapper\
**Created:** [July 25, 2022, 5:26pm UTC](https://community.pix4d.com/t/quality-check-on-gcps-gcps-are-used-and-the-gcp-error-is-more-than-4-times-the-average-gsd/23361 "2022-07-25T17:26:51Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![sal](https://avatars.discourse-cdn.com/v4/letter/s/58f4c7/32.png) [@sal](https://community.pix4d.com/u/sal)\
**Post date:** [July 25, 2022, 5:26pm UTC](https://community.pix4d.com/t/quality-check-on-gcps-gcps-are-used-and-the-gcp-error-is-more-than-4-times-the-average-gsd/23361/1 "2022-07-25T17:26:51Z")

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I have run this project several times, carefully marking GCP points each time, but still getting red exclamation point for Georeferencing in the Quality Check/Quality Report. The GCPs were located with RTK GNSS system. I cannot find reason or error in workflow that would cause a GCP error is more than 4 times the average GSD.

Quality Report is attached. Thanks for any quidance

[AccuracyAssessment2022-06-15\_report.pdf](https://community.pix4d.com/uploads/short-url/okA4aMtmaE1hfNL9lCl2rDki3xS.pdf) (1.3 MB)

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**Author:** ![Andrew\_Milanes](https://avatars.discourse-cdn.com/v4/letter/a/a4c791/32.png) [@Andrew\_Milanes](https://community.pix4d.com/u/Andrew_Milanes)\
**Post date:** [July 26, 2022, 12:35am UTC](https://community.pix4d.com/t/quality-check-on-gcps-gcps-are-used-and-the-gcp-error-is-more-than-4-times-the-average-gsd/23361/2 "2022-07-26T00:35:39Z")

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Since the texture of your project is very homogeneous (grass field), I would try changing the calibration method from standard to alternative. Also, what was your flight altitude and overlap?

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**Author:** ![Rosana\_Lin](https://avatars.discourse-cdn.com/v4/letter/r/71e660/32.png) [@Rosana\_Lin](https://community.pix4d.com/u/Rosana_Lin)\
**Post date:** [July 27, 2022, 10:04am UTC](https://community.pix4d.com/t/quality-check-on-gcps-gcps-are-used-and-the-gcp-error-is-more-than-4-times-the-average-gsd/23361/3 "2022-07-27T10:04:08Z")

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Hi Jon,

From the quality report, we can see there is a difference between the initial position and the computed position.  
 ![](https://global.discourse-cdn.com/pix4d/original/2X/9/948ace4065814ae16a1555571f2cf57022a8eb47.png)

If you believe your dataset has good image geolocation, please select Accurate Geolocation and Orientation in Step 1. Initial Processing \> Calibration \> Calibration Method \> Accurate Geolocation and Orientation. Try also reducing the image scale to 1/2 or 1/4. You can take a look at this article. [Menu Process \> Processing Options… \> 1. Initial Processing \> Calibration](https://support.pix4d.com/hc/en-us/articles/205327965-Menu-Process-Processing-Options-1-Initial-Processing-Calibration?source=search)

 ![](https://global.discourse-cdn.com/pix4d/original/2X/7/78b8325a9085944a399df852bdec07e25290b192.png)

I hope this is helpful.

Sincerely,  
Rosana

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**Author:** ![sal](https://avatars.discourse-cdn.com/v4/letter/s/58f4c7/32.png) [@sal](https://community.pix4d.com/u/sal)\
**Post date:** [July 27, 2022, 4:15pm UTC](https://community.pix4d.com/t/quality-check-on-gcps-gcps-are-used-and-the-gcp-error-is-more-than-4-times-the-average-gsd/23361/4 "2022-07-27T16:15:48Z")

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Thank you Andrew - I will give that a try. We flew 2 missions: one at 40 meters and the other at 50 meters. Working with the 40 meter AGL images first where I encountered the error.