when you are exporting your results from RealityCapture you have more options there regarding to selection of the coordinate system. There could be two cases. First case is non georeferenced environment, the second case is georeferenced.
When you have non georeferenced project you can export in Grid or Same as XMP coordinate system.
When you have georeferenced project there are added two options: Output coordinate system and Shifted output coordinate system.
Grid plane coordinate system is related to the grid which is visible in 3D view. It can be consider as local coordinate system. The axis are oriented (when you are looking from above): Y is pointing to north and it is a green arrow, X is pointing to east, it is a blue arrow and Z is pointing up as red arrow.
Grid coordinate system is related to an actual 3D view and model's position, so if you use Set ground plane after model computation, there will be different grid plane model coordinates as before this change.
On this image you can see the model placed to the grid's zero position. This means that the model's coordinates will be around 0 for X and Y axis.
Same as XMP
XMP coordinate system is related to the XMP data and could be different regarding to grid coordinate system. This is the system and coordinates which you get after the first images' alignment.
On this image you can see the previous model in Same as XMP coordinate system. The model is not on the zero Z grid position but it id slightly in the air:
The good explanation of the difference between these exports' coordinates system is visible when we compare two exported models in one application in their basic positions.
On this image, upper model is exported in Same as XMP coordinate system and lower model is exported in the Grid plane coordinate system.
This option is only available when your project is georeferenced (in local or global coordinates). Project output coordinate system is one which is set in the application settings. To set the output coordinate system go to Workflow tab/Application/Settings/Coordinate systems. You can use local Euclidian coordinate system, one of the predefined global coordinate systems or one of your own coordinate systems (https://support.capturingreality.com/hc/en-us/articles/4771191909148-Set-your-own-global-or-local-coordinate-system).
Shifted project output
This coordinate system has the same orientation as project output coordinate system but it is moved to the centre of the reconstruction. Basically, the zero of this coordinate system is located in the zero of the grid and it is in the centre of the firstly aligned component.