# Orthomosaic Accuracy **URL:** \ **Category:** PIX4Dmapper Questions/Troubleshooting\ **Created:** [August 17, 2018, 3:48pm UTC](https://community.pix4d.com/t/orthomosaic-accuracy/7062 "2018-08-17T15:48:47Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![Brad\_Johnson](https://avatars.discourse-cdn.com/v4/letter/b/f475e1/32.png) [@Brad\_Johnson](https://community.pix4d.com/u/Brad_Johnson)\ **Post date:** [August 17, 2018, 3:48pm UTC](https://community.pix4d.com/t/orthomosaic-accuracy/7062/1 "2018-08-17T15:48:47Z")
I’m working on a conceptual redesign of an intersection, and we usually use orthomosaics to set our alignments and LiDAR data that is available to us statewide for a DTM. The orthomosaics available to us statewide are pretty low quality, so I would like to start using orthomosaics created from Pix4D on all of our projects that require preliminary design. I flew a 63 acre area at 375’ with a Mavic Pro, and the orthomosaics created were very high quality. I used 5 GCPs spread around the edges of the project that were spaced 500’-800’ apart. My issue is that when I compare common points on the Pix4D generated orthomosaic to the orthomosaics available to us statewide there is a 3’-10’ discrepancy. Should I be trusting the Pix4D generated orthomosaic? Is there anything wrong with the process from which I generated the orthomosaic that I described above? I trust the accuracy of all GCPs used and they were all present in at least 15 images. ---
**Author:** ![Jaakko\_Laihola](https://avatars.discourse-cdn.com/v4/letter/j/f6c823/32.png) [@Jaakko\_Laihola](https://community.pix4d.com/u/Jaakko_Laihola)\ **Post date:** [August 17, 2018, 4:15pm UTC](https://community.pix4d.com/t/orthomosaic-accuracy/7062/2 "2018-08-17T16:15:04Z")
Could you share the quality report? 5 GCP’s in 63 acre (~25ha area) is too low in my opinion. Few days back I did a job 30ha job and used 43 GCP’s and 15 of the as checkpoints. That gave me enough information to verify the correctness of my otrho and DTM.  [https://support.pix4d.com/hc/en-us/articles/115000140963-Difference-between-a-ground-control-point-and-a-checkpoint](https://support.pix4d.com/hc/en-us/articles/115000140963-Difference-between-a-ground-control-point-and-a-checkpoint) ---
**Author:** ![John\_Meyer](https://avatars.discourse-cdn.com/v4/letter/j/c77e96/32.png) [@John\_Meyer](https://community.pix4d.com/u/John_Meyer)\ **Post date:** [August 30, 2018, 12:49pm UTC](https://community.pix4d.com/t/orthomosaic-accuracy/7062/3 "2018-08-30T12:49:47Z")
[https://hmbpe-my.sharepoint.com/🅱/p/jmeyer/EUyrm6GRhItInY1V29wYGtIBnE8DAZw\_XE-0lcxZ-J6hSg?e=oXdFlX](https://hmbpe-my.sharepoint.com/:b:/p/jmeyer/EUyrm6GRhItInY1V29wYGtIBnE8DAZw_XE-0lcxZ-J6hSg?e=oXdFlX)  Here is the quality report for the aforementioned project. I worked with Brad on the project and actually processed the data on my machine. Can I asked what you used for GCP’s on your project? Setting 43 CP’s with targets would take quite a long time.  ---
**Author:** ![Jaakko\_Laihola](https://avatars.discourse-cdn.com/v4/letter/j/f6c823/32.png) [@Jaakko\_Laihola](https://community.pix4d.com/u/Jaakko_Laihola)\ **Post date:** [August 30, 2018, 1:32pm UTC](https://community.pix4d.com/t/orthomosaic-accuracy/7062/4 "2018-08-30T13:32:36Z")
You were flying Mavic Pro and it has rolling shutter. Try to run the project again with rolling shutter effect corrected [https://support.pix4d.com/hc/en-us/articles/208460436-How-to-correct-for-the-Rolling-Shutter-Effect](https://support.pix4d.com/hc/en-us/articles/208460436-How-to-correct-for-the-Rolling-Shutter-Effect) I used spray paint to mark GCP’s and RTK-GPS