# Limitations of the position of GCPs **URL:** \ **Category:** PIX4Dmapper Questions/Troubleshooting\ **Created:** [November 19, 2018, 10:10am UTC](https://community.pix4d.com/t/limitations-of-the-position-of-gcps/7554 "2018-11-19T10:10:54Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![Jaydeb\_Dutta](https://avatars.discourse-cdn.com/v4/letter/j/b4bc9f/32.png) [@Jaydeb\_Dutta](https://community.pix4d.com/u/Jaydeb_Dutta)\ **Post date:** [November 19, 2018, 10:10am UTC](https://community.pix4d.com/t/limitations-of-the-position-of-gcps/7554/1 "2018-11-19T10:10:54Z")
Dear Sir/Mam, We have a project of survey of area approx 260 Sqr Kms. We are using Inspire 1. For better result, we need GCPs. So we need some informations from you those are following: 1. Minimum distance b/w two GCP points? 2. How should we put the GCPs in processing time? 3. When we process some images at a time for an area & there is no GCP within that range but we have taken far away from that area,then how should we import those GCPs in that processing area?  We are waiting for your valuable suggestion. Thanks & Regards, Jaydeb ---
**Author:** ![Aaron\_Woods2](https://sea2.discourse-cdn.com/pix4d/user_avatar/community.pix4d.com/aaron_woods2/32/421_2.png) [@Aaron\_Woods2](https://community.pix4d.com/u/Aaron_Woods2)\ **Post date:** [November 20, 2018, 6:19pm UTC](https://community.pix4d.com/t/limitations-of-the-position-of-gcps/7554/2 "2018-11-20T18:19:26Z")
Hi Jaydeb, Thanks for your interest in Pix4D software solutions.  I understand how frustrating it can be to get up to speed on how to create accurate photogrammetry deliverables.   1.  There is no “Set” minimum distance between two GCP points.  You need to take into account your project Ground Sampling Distance, the required level of Accuracy for the project and the local terrain variability.  Typically I would suggest having a GCP ~500 feet, but this distance may not be ideal for every project. 2.  Pix4D offers a number of support articles on how to implement GCP’s a couple of good ones to reference are: [How to add / import GCPs in the GCP/MTP Manager](https://support.pix4d.com/hc/en-us/articles/202560039-How-to-add-import-GCPs-in-the-GCP-MTP-Manager) & [Using GCPs](https://support.pix4d.com/hc/en-us/articles/202558699-Using-GCPs) 3.  The GCP data you wish to use for a project must be visible in multiple photos of that project.  If you have sub projects without GCP points being shown, these sub projects will need to be merged into data that has the GCP data visible in it. I also encourage you to participate in a[Pix4D User Workshop](https://www.pix4d.com/services/training-certification/workshops).  These 2 day user workshops really help new users establish efficient work flows to achieve the best results. Regards Aaron Woods   ---
**Author:** ![Jaydeb\_Dutta](https://avatars.discourse-cdn.com/v4/letter/j/b4bc9f/32.png) [@Jaydeb\_Dutta](https://community.pix4d.com/u/Jaydeb_Dutta)\ **Post date:** [November 21, 2018, 6:10am UTC](https://community.pix4d.com/t/limitations-of-the-position-of-gcps/7554/3 "2018-11-21T06:10:35Z")
Dear Sir, First of all I need to understand what is the “Subproject” actually means. For my project,i have total near about 4 lac images. And i usually process 1500-2000 images at a time. So i am getting set of small orthomosaic tiff files. But for each set of 1500-2000 images,there is no GCPs. So my question is How could i get accurate result in respect to those GCPs in every orthomosaic file. How could i merge the “without GCP ortho file” with “ortho file having GCP”.  I am very much interested to know about this software with very detailing. Thanks & Regards, Jaydeb ---
**Author:** ![Jaydeb\_Dutta](https://avatars.discourse-cdn.com/v4/letter/j/b4bc9f/32.png) [@Jaydeb\_Dutta](https://community.pix4d.com/u/Jaydeb_Dutta)\ **Post date:** [November 24, 2018, 12:18pm UTC](https://community.pix4d.com/t/limitations-of-the-position-of-gcps/7554/4 "2018-11-24T12:18:25Z")
Dear Sir, I am waiting for your reply.  And for training purpose is there any scope through online or any places in India?  Regards, Jaydeb ---
**Author:** ![Aaron\_Woods2](https://sea2.discourse-cdn.com/pix4d/user_avatar/community.pix4d.com/aaron_woods2/32/421_2.png) [@Aaron\_Woods2](https://community.pix4d.com/u/Aaron_Woods2)\ **Post date:** [November 26, 2018, 4:36pm UTC](https://community.pix4d.com/t/limitations-of-the-position-of-gcps/7554/5 "2018-11-26T16:36:01Z")
Hi Jaydeb, The projects without GCP points visible will need to be “Merged” with the projects that do have/show your GCP data/points.  I would refer you to the support article titled [Manual Tie Points and GCPs in merged project](https://support.pix4d.com/hc/en-us/articles/202559439-Manual-Tie-Points-and-GCPs-in-merged-project) [Pix4D also offers a Video that covers Merging](https://www.youtube.com/watch?v=Wu-A64egnb4) as well  Pix4D staff can arrange an an online training as well, you can re[ach out regarding your specific needs here](https://www.pix4d.com/services/training-certification/request-a-quote). Happy Holidays, Aaron. ---
**Author:** ![Jaydeb\_Dutta](https://avatars.discourse-cdn.com/v4/letter/j/b4bc9f/32.png) [@Jaydeb\_Dutta](https://community.pix4d.com/u/Jaydeb_Dutta)\ **Post date:** [December 5, 2018, 11:34am UTC](https://community.pix4d.com/t/limitations-of-the-position-of-gcps/7554/6 "2018-12-05T11:34:31Z")
Dear Sir, After adding GCP via basic editor,when i click “Reoptimize” option the application is automatically closed. I have tried 2 to 3times but the same problem is happening. What should be done? System Configuration is i9 128 GB RAM 1 TB SSD 1 TB HDD. Thanks & Regards, Jaydeb   ---
**Author:** ![Aaron\_Woods2](https://sea2.discourse-cdn.com/pix4d/user_avatar/community.pix4d.com/aaron_woods2/32/421_2.png) [@Aaron\_Woods2](https://community.pix4d.com/u/Aaron_Woods2)\ **Post date:** [December 5, 2018, 7:18pm UTC](https://community.pix4d.com/t/limitations-of-the-position-of-gcps/7554/7 "2018-12-05T19:18:45Z")
Hi Jaydeb, I’m sorry to hear that you’ve continued to run into issues with your project.  The specifications you list above sound like they are more than adequate to run Pix4D.  Would it be possible to share a copy of your project quality report along with a copy of the Pix4D LOG file?  These files would be helpful for Pix4D support to determine what is causing the issue.  Is there a reason you are using the Basic editor rather than the Raycloud editor? [Menu View \> Log Outpu](https://support.pix4d.com/hc/en-us/articles/207772556-Menu-View-Log-Output)t The Log file is located in the Outputs folder at the root level and will be named “projectname”.txt I look forward to your response. Aaron