# Optimizing with GCPS fails **URL:** \ **Category:** PIX4Dmapper Questions/Troubleshooting\ **Created:** [January 17, 2019, 1:59pm UTC](https://community.pix4d.com/t/optimizing-with-gcps-fails/7846 "2019-01-17T13:59:16Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![Lander\_Van\_Tricht](https://avatars.discourse-cdn.com/v4/letter/l/bc8723/32.png) [@Lander\_Van\_Tricht](https://community.pix4d.com/u/Lander_Van_Tricht)\ **Post date:** [January 17, 2019, 1:59pm UTC](https://community.pix4d.com/t/optimizing-with-gcps-fails/7846/1 "2019-01-17T13:59:16Z")
Hello I have added GCPs to my project, For some of them, it works very well and the blue circle (projected GCP) is very close to the real position for all the images on which it is visible. However, for other GCPS, the error in x,y,z remains high and as I see, the blue circle shifts for every images around the GCPs. That means that for some images it is correct in the middle but certainly not for all. The green cross does the same. Have can I solve this? Gr Lander ---
**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:** [January 18, 2019, 2:25pm UTC](https://community.pix4d.com/t/optimizing-with-gcps-fails/7846/2 "2019-01-18T14:25:13Z")
Hi Lander, Could you please share the quality report and some screenshots that depict the issue so we get a better overview of the situation? Is there something special about the affected GCPs, for example, are they close to the edge of the project?  Best, ---
**Author:** ![Lander\_Van\_Tricht](https://avatars.discourse-cdn.com/v4/letter/l/bc8723/32.png) [@Lander\_Van\_Tricht](https://community.pix4d.com/u/Lander_Van_Tricht)\ **Post date:** [January 21, 2019, 11:34am UTC](https://community.pix4d.com/t/optimizing-with-gcps-fails/7846/3 "2019-01-21T11:34:36Z")
Hello   The GCPs are not really at the edge. Besides, it is strange that for other GCPs very nearby, the accuracy is high…     How can I upload thequality report as it is a pdf file Lander   ---
**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:** [January 21, 2019, 1:40pm UTC](https://community.pix4d.com/t/optimizing-with-gcps-fails/7846/4 "2019-01-21T13:40:57Z")
You can upload the .pdf report [here](https://pix4d365-my.sharepoint.com/:f:/g/personal/blaz_vidmar_pix4d_com/EqE9kp6iDL5Ehfegy3XemaABw4_mWogkPdgSfWmiqe_cEg?e=Ahy0xx). ---
**Author:** ![Lander\_Van\_Tricht](https://avatars.discourse-cdn.com/v4/letter/l/bc8723/32.png) [@Lander\_Van\_Tricht](https://community.pix4d.com/u/Lander_Van_Tricht)\ **Post date:** [January 21, 2019, 1:44pm UTC](https://community.pix4d.com/t/optimizing-with-gcps-fails/7846/5 "2019-01-21T13:44:39Z")
Ok, done!   ---
**Author:** ![Lander\_Van\_Tricht](https://avatars.discourse-cdn.com/v4/letter/l/bc8723/32.png) [@Lander\_Van\_Tricht](https://community.pix4d.com/u/Lander_Van_Tricht)\ **Post date:** [January 22, 2019, 10:02pm UTC](https://community.pix4d.com/t/optimizing-with-gcps-fails/7846/6 "2019-01-22T22:02:25Z")
I added the quality report, do I process it in a wrong manner? Lander ---
**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:** [January 25, 2019, 4:00pm UTC](https://community.pix4d.com/t/optimizing-with-gcps-fails/7846/7 "2019-01-25T16:00:45Z")
Thank you for sharing the report. I find the project very interesting! Is it a glacier in Switzerland? I had a close look at the report and notice that there were 2 camera models detected in the project and that each calibrated a bit differently. Since the camera parameters are not the same this could explain the behavior that you see; projected crosses on the images vary. At the moment I would recommend the following: 1. Processing the flights separately in subprojects and marking the GCPs and MTP in the subprojects. 2. Making sure that, before merging the projects, all the subprojects are processed successfully and there are no issues present, e.g. bad camera optimization, uncalibrated camera or multiple blocks. You can use the [All-Prior calibration option](https://support.pix4d.com/hc/en-us/articles/205327965-Menu-Process-Processing-Options-1-Initial-Processing-Calibration) if the camera optimization drifts too far from the initial value. 3. Merging the subprojects as described in the [How to merge projects](https://support.pix4d.com/hc/en-us/articles/202558529-How-to-merge-projects) article. If you will still face the same issue after using the proposed workflow, please upload the project on the cloud and I will investigate further.    ---
**Author:** ![Lander\_Van\_Tricht](https://avatars.discourse-cdn.com/v4/letter/l/bc8723/32.png) [@Lander\_Van\_Tricht](https://community.pix4d.com/u/Lander_Van_Tricht)\ **Post date:** [January 25, 2019, 7:39pm UTC](https://community.pix4d.com/t/optimizing-with-gcps-fails/7846/8 "2019-01-25T19:39:06Z")
Yes the Morteratsch glacier in Switzerland! IT is strange dingen I idee the simulator drone for the different flights… I Will try your work flow proposal! Thanks ---
**Author:** ![Lander\_Van\_Tricht1](https://avatars.discourse-cdn.com/v4/letter/l/779978/32.png) [@Lander\_Van\_Tricht1](https://community.pix4d.com/u/Lander_Van_Tricht1)\ **Post date:** [February 11, 2019, 1:04pm UTC](https://community.pix4d.com/t/optimizing-with-gcps-fails/7846/9 "2019-02-11T13:04:25Z")
Hi I tried to process a particular area separately but it still gives erroneous results. I added more than 5 GCPs but it seems that there are only 2 of them taken into account. The report can be find here [https://pix4d365-my.sharepoint.com/personal/blaz\_vidmar\_pix4d\_com/Documents/Forms/All.aspx?RootFolder=%2Fpersonal%2Fblaz\_vidmar\_pix4d\_com%2FDocuments%2F65653&FolderCTID=0x012000CB9594410451104484ACD55517736701](https://pix4d365-my.sharepoint.com/personal/blaz_vidmar_pix4d_com/Documents/Forms/All.aspx?RootFolder=%2Fpersonal%2Fblaz_vidmar_pix4d_com%2FDocuments%2F65653&FolderCTID=0x012000CB9594410451104484ACD55517736701) under the name persmidng   Hope that you find the problem… Gr  Lander