# Collaborative Marking GCPs For a large number of control points in a project, Get3D Mapper supports multiple computers to mark GCPs together to enhance work efficiency.

Get3D Mapper supports opening sub-projects on multiple computers, and the only operation that sub-projects can do is to edit control points. When the main project enters the interface of editing control points, it locks all control points by default. When the main project releases a portion of the control points, the secondary project can lock that portion of the released control points and perform Mark GCPs operations. When multiple computers have finished collaborating on the marking, click on each computer to save the control point information. Finally, the main project will update the control point information.

The specific operation is as follows: 1\) In the main project in the submit AT interface click **Edit GCP** to enter the Edit Control Points interface. **Import the control point file** and **select the correct coordinate system**. 2\) Select some control points and click **Unlock**.

3\) Open the project on another computer. When you open it, the default prompt is that the project opened here is a sub-project, and you can only edit control point operations.

4\) Enter the Edit Control Points screen, click **Update** to see the unlocked control points, and then you can Mark GCPs on the machine after locking it.

For more details on marking GCPs, refer to the section [Edit Control Points](https://docs.get3d.ai/user-help-center/get3d-mapper/getting-started/edit-control-points) 5\) When sub-project has done marking, click **Update** and **Save**.

Update and Save Sub-Project Marking Results

6\) After completing all marking points operation, click **Update**, **Save** in the main project to exit this screen.