Photogrammetric surveying of ships is a complex exercise due to the nature of the objects to be recorded. The advantage of a complete survey, as opposed to a half-hull survey, is that it allows the deformations of the structures to be identified, evaluated and diagnosed.
In the example below, the demonstration is made on a model. The principles and difficulties are identical to a 1:1 scale model, but with much better accessibility. For examples of real boats, see the following pages
A series of 144 photos were made for this example. The photos are taken by rotating around the subject, taking care to have a coverage rate of 60% or more. Particular care must be taken with the coverage of the bow and stern.
Create a new Object
Select 100 photos
Give a name and press start
The photos are uploaled. The process is done remotely.
When done, the model can be downloaded
It appears in My Computer files
The model can be cleaned up
The meshing is very dense
After clean up to be compared with the MetaMesh version.
Metamesh is a leading photogrammetry that requires a huge computer power as everything is done localy.
The process is quite linear, the interface helps to follow the steps one after the other.
Then Workflow Align Photos
High gives good results if the photos have a good coverage rate.
Once done a parse Cloud is done.
Visualizing the cameras allows to verify the good coverage.
Next step is Workflow build Dense Cloud
To better isolate the subject choose Aggressive
In our example the model gives a total of 5.586.475 points
Next step is the meshing
Workflow Build Mesh, choose Dense Cloud
Once done we see that we can see that the hull is quite complete, problems are visible for all the very delicate objects and elements.
Final step texturing
Workflow Build Texture
Duplicate the model to keep the original version….just in case. Right Mouse Button on the chunk name and Duplicate.
To scale the model, add at least 3 markers. Measure distances on the real model and set coordinates for the determined points.
Never forget to reset
Decimation will simplify the geometry -> Tools/Mesh/decimate
When not replacing the original model, it’s possible to keep the list of all resolutions
The 50 000 faces model is exported
Remeshing – Retopology
Instant Meshes is a very good software to simplify a complex geometry. It can be found here : https://github.com/wjakob/instant-meshes
Import the OBJ and set the target count. Here a high resolution is chosen
When solved, the little squares indicate the result
Export mesh to get the final result -> Extract Mesh
Result with 30 faces
With 200 000
The first one is more than enough to be reworked in Rhino with Grasshopper.
Meshmixer (https://www.meshmixer.com/) can be used to fix some remaining errors
Now Grasshopper can be used to redraw the hull
After importing the mesh in Rhino, a simple definition in Grasshopper allows to extract sections as curves.
As the lowest part of the Hull as a bit messy, curves would have to be redrawn a bit
Ready for a VR experience?