# GCP

**URL:** <https://community.pix4d.com/t/gcp/7032>\
**Category:** PIX4Dmapper Questions/Troubleshooting\
**Created:** [August 12, 2018, 2:28am UTC](https://community.pix4d.com/t/gcp/7032 "2018-08-12T02:28:43Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![Tido\_Djedjemoule](https://avatars.discourse-cdn.com/v4/letter/t/c57346/32.png) [@Tido\_Djedjemoule](https://community.pix4d.com/u/Tido_Djedjemoule)\
**Post date:** [August 12, 2018, 2:28am UTC](https://community.pix4d.com/t/gcp/7032/1 "2018-08-12T02:28:43Z")

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First of all, I would like to think PIX4D Mapper for one of the greatest software ever created. In my first post, I mentionned that some GCPs coudn’t match the indicated locations. There IS a big problem of accuray. Please,tell me something. Why can, in a same project, some GCP match locations after reoptmizing and some others simply cannot. I mean, after reoptimizing the project with 12 GCP, 10 perfectly matched the model and 2 others are vertically shifted.

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Note that the images have the same coordinate system that the GCP.  
WGS84/ UTM zone 30 N (egm86)

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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:** [August 14, 2018, 7:24am UTC](https://community.pix4d.com/t/gcp/7032/2 "2018-08-14T07:24:41Z")

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Hello Tido,

Thanks for your message.

As you have an open ticket in our support site, I will follow it up there.

Regards.