# GCP does not match altitude

**URL:** <https://community.pix4d.com/t/gcp-does-not-match-altitude/3633>\
**Category:** PIX4Dmapper Questions/Troubleshooting\
**Created:** [January 5, 2018, 6:17pm UTC](https://community.pix4d.com/t/gcp-does-not-match-altitude/3633 "2018-01-05T18:17:13Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Patricia\_Sammia](https://avatars.discourse-cdn.com/v4/letter/p/97f17d/32.png) [@Patricia\_Sammia](https://community.pix4d.com/u/Patricia_Sammia)\
**Post date:** [January 5, 2018, 6:17pm UTC](https://community.pix4d.com/t/gcp-does-not-match-altitude/3633/1 "2018-01-05T18:17:13Z")

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Hello folks. Can please someone help me? I am having problems with the GCP and Raycloud in step1. The project has 9 GCPs and only one is not macthing the altitude of the GCP and Raycloud. The others are fine.&nbsp;  
I already did reoptimization and still the same. The difference is about 9.2 metters. Please see the image. Thanks guys

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<div class="post-metadata">

**Author:** ![Patricia\_Sammia](https://avatars.discourse-cdn.com/v4/letter/p/97f17d/32.png) [@Patricia\_Sammia](https://community.pix4d.com/u/Patricia_Sammia)\
**Post date:** [January 5, 2018, 6:29pm UTC](https://community.pix4d.com/t/gcp-does-not-match-altitude/3633/2 "2018-01-05T18:29:15Z")

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here is the Quality Report. I’m wonder about the blocks. Is too many. Is normal?&nbsp;

Many blocks is meaning that the project are not accurate or poor?

What the meaning of many blocks?

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**Author:** ![Rhea\_Garratt](https://sea2.discourse-cdn.com/pix4d/user_avatar/community.pix4d.com/rhea_garratt/32/403_2.png) [@Rhea\_Garratt](https://community.pix4d.com/u/Rhea_Garratt)\
**Post date:** [January 9, 2018, 12:18pm UTC](https://community.pix4d.com/t/gcp-does-not-match-altitude/3633/3 "2018-01-09T12:18:45Z")

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Hi Sammia,

Thank your for the screenshots.

The&nbsp;_Quality Check_&nbsp;section of the quality report is very useful, as it informs of existing issues in a project. In your case, there are issues with the dataset calibration and the GCP error: all images should have been successfully calibrated, in one single block, and the RMS error should be lower than 2\*GSD. See the article sections linked to these errors [here](https://support.pix4d.com/hc/en-us/articles/202558689-Quality-Report-Help#label101)and [here](https://support.pix4d.com/hc/en-us/articles/202558689-Quality-Report-Help#label104).

It is important to address these errors first, because it is probable the offset issue with GCP no. 3 will be solved as a result. Indeed, the blocks were created by the software, because there were not enough matches between them for a global&nbsp;optimization. The blocks are not aligned, which is why some areas do not fit your GCPs.&nbsp;

However, without more information about your project, it is hard to point to a specific cause for the uncalibrated images.

- Could you please provide us with a link to you quality report (Google Drive, Dropbox, etc.), as well as 5 consecutive images from your dataset?&nbsp;
- Also, does the dataset consist of images from different flights?

Looking forward to your answer.