GCP accuracy & Other

[Dini1984]

Hello,
Can i ask some questions?
1.Firstly, for a 6 hectare surface, with 5 gcp, is it enough to have a good accuracy in x,y,z?
2.In your workflow, Edit Geometry, why it is used? and when do u understand why you have to use it? Be cause i dont understand how to indicate faces?
3. What do u mean with 'polygonal models'?
4. Do u have any idea how to export just a part of the points? I mean just points with 3D data or 3D breaklines....Is there any way to do that?

[SAV]

Hi Dini1984,

Hello,
Can i ask some questions?
1.Firstly, for a 6 hectare surface, with 5 gcp, is it enough to have a good accuracy in x,y,z?

I suggest to place 9-15 GCPs. Use about 80% of them as control points and the rest as check points. It is important to distribute all GCPs throughout the survey area (e.g., they should not lie on the same line). You should also properly survey them using a cm accuracy RTK GPS or total station.

2.In your workflow, Edit Geometry, why it is used? and when do u understand why you have to use it? Be cause i dont understand how to indicate faces?

I am not sure what you mean with that. Edit the geometry of the mesh? Which part of the workflow are you talking about?

3. What do u mean with 'polygonal models'?

3D models are represented as a series of connected polygons that form a mesh. Most of the time triangles are used to form these meshes, that's why it is called 'mesh triangulation'.

4. Do u have any idea how to export just a part of the points? I mean just points with 3D data or 3D breaklines....Is there any way to do that?

Duplicate your chunk and then delete all points that you don't want. Then export whatever is left. Alternatively, export all your points and crop/segment the point cloud using CloudCompare (free and open-source)


Regards,
SAV

[Dini1984]

Thanks SAV,
For all your time.
Can you tell me if there is any way to export point cloud less than 'dense cloud'?  Because there is only one option, that is sparse cloud....

[SAV]

Hi Dini1984,

If you build your dense cloud at a lower quality, it will have less points (= smaller file size). Unfortunately there is no option built into Photoscan to subsample the dense point cloud (only works for the mesh).

However, you can export the full dense point cloud and then perform the subsampling in CloudCompare (free and open-source). It is a very simply procedure. Here are the details:
http://www.cloudcompare.org/doc/wiki/index.php?title=Edit%5CSubsample

All the best.

Regards,
SAV