# Elevation Issues
**URL:** https://community.pix4d.com/t/elevation-issues/8662
**Category:** PIX4Dmapper Questions/Troubleshooting
**Created:** [July 9, 2019, 4:09pm UTC](https://community.pix4d.com/t/elevation-issues/8662 "2019-07-09T16:09:36Z")
**Posts on this page:** 4
**Page:** 1
### Author:  [@Nathan\_Northey](https://community.pix4d.com/u/Nathan_Northey)
#### Post date: [July 9, 2019, 4:09pm UTC](https://community.pix4d.com/t/elevation-issues/8662/1 "2019-07-09T16:09:36Z")
I am having some trouble with elevation data gathered within the generated point cloud for a site I flew. All elevations across the site seem to be off by 1’-2’ on average. I am comparing to a boots on the ground survey done by our survey team. I was wondering is there was a processing step I did wrong? O r perhaps an adjustment that can be made? I will include the Quality Report as an image. Thank you in advance for any help!
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### Author:  [@Derek\_Bendell](https://community.pix4d.com/u/Derek_Bendell)
#### Post date: [July 10, 2019, 2:30pm UTC](https://community.pix4d.com/t/elevation-issues/8662/2 "2019-07-10T14:30:39Z")
Is your GCP data collected and provided to you by the field crew or did you collect your GCPs separate from the work they did?
What did you set for your vertical coordinate system?
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### Author:  [@Erik\_Graham](https://community.pix4d.com/u/Erik_Graham)
#### Post date: [July 16, 2019, 4:12pm UTC](https://community.pix4d.com/t/elevation-issues/8662/3 "2019-07-16T16:12:50Z")
It also seems like your front overlap is really inconsistent. I’m guessing your memory card isn’t fast enough to process pics a the speed you’re flying/shooting.
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### Author:  [@Alice\_Bonfiglio](https://community.pix4d.com/u/Alice_Bonfiglio)
#### Post date: [July 22, 2019, 12:25pm UTC](https://community.pix4d.com/t/elevation-issues/8662/4 "2019-07-22T12:25:12Z")
Hi Nathan,
Which is the vertical coordinate system used for your GCPs? Are the altitudes defined in US foot and referred to the GRS 80 ellipsoid? Which points are you considering to check the accuracy of the project? Do you see this 1’-2’ difference also around the GCPs? I see from the quality report that the sigma of the error in Z is good (0.1 US foot).
The number of 2D keypoints matches is also low. This could be linked to the distribution of the acquired image and might cause overall reduced accuracy. Do the images have the same light conditions? You can also try to halve the keypoint image scale from **Process \> Processing Options \> 1. Initial Processing \> General \> Keypoints Image Scale**.