# Forum

### Author Topic: All marker coordinates deleted if any one field (x,y,z) cleared  (Read 7783 times)

#### andyroo

• Sr. Member
• Posts: 441
##### All marker coordinates deleted if any one field (x,y,z) cleared
« on: July 03, 2012, 07:23:42 PM »
Just noticed that if all of the numbers are deleted out of any field, all coordinates for that marker are deleted. In other words if I start to enter Z, then decide I just want to use x,y coordinates instead, and delete z, then press <enter>, I have to re-enter x and y.

I don't know if this is a bug, but for me it is an undesired feature.

#### Alexey Pasumansky

• Agisoft Technical Support
• Hero Member
• Posts: 14999
##### Re: All marker coordinates deleted if any one field (x,y,z) cleared
« Reply #1 on: July 03, 2012, 07:30:06 PM »
Hello Andy,

Since it is impossible to use GCPs with one or two unknown coordinates it is required to assign values to all coordinates. Even you do not know one of them, for example, Z, you can use approximate or average values, though it leads to the lower accuracy.
Best regards,
Alexey Pasumansky,
Agisoft LLC

#### andyroo

• Sr. Member
• Posts: 441
##### Re: All marker coordinates deleted if any one field (x,y,z) cleared
« Reply #2 on: July 09, 2012, 03:43:31 AM »
Hi Alexey,

Thank you for the reply. I understand that you need to have a value for x, y, and z for each GCP, but that was not my point - if I clear all of the numbers out of any one field then exit that field, instead of replacing only that field (x, y, or z) with 0.00, all three fields go to 0.00, and I have to go back and re-enter all three instead of just one. I would rather just have the one field go to 0.00 - then I could look up, estimate, calculate etc for just the one field. In other words, I should have to explicitly delete as well as explicitly enter a coordinate for x, y, and z individually.

That said,  generally I have had good results for areas with poor z control just using three points with x,y known and setting z to zero (~ 1 m horizontal error in a ~1.5 km x 4 km area). This minimizes (helmert?) distortion of the orthoimage produced by PS and ties it to known coordinates. For the purposes of geomorphic analysis and change detection this is good enough, and since I don't have known z in these areas (it was a lake) I think I would just cause more issues by adding approximate z.