Scan Density + Resulting Mesh Quality

There are 3 density levels that you can set the BLK360 to prior to scanning:ipad_in-app_scan_settings

These are accessed via the settings ‘cog’ on the iPad app..

 

 

 

 

 

 

generate_mesh

 

If you are wanting Autodesk to generate a mesh for you then you once again have 3 levels – this time ‘Mesh Quality’ … you have seen this image already too.

 

 

 

 

 

 

My test scan is a stone monument in the Quadrangle at Dundee University – pictured below on a far sunnier day than when the scans were taken.

quad_sunny_day

I scanned the ‘4 station’ scene in high and low scan densities so that i could compare them.  I scanned at medium density too but the results are just so ‘samey’ that they get confusing.

E:LASER SCANNINGBLK360_BLoGSTATS Layout1 (1)

From this comparison you can see that scanning high density but requesting a low quality model results in a mesh that is slightly lower than if you had scanned at low density.   It’s as if the meshing software on the A360 cloud applies it’s own tessellation/triangulation no matter what density of mesh you upload.   It’s the quality of the mesh you request that determines how many triangles are generated.   See the very end of this post for a detailed analysis of 100 x 100mm.

Here’s what the models and scans look like – we start with Low Density Scan + Low Quality Mesh.

lores_lowquality_800

 

Below is Low Density Scan + High Quality Mesh – it seems quite ‘noisy’ in areas – as if the meshing routine has added in additional information unnecessarily.

lores_highquality_800

We now move to the High Density Scan + Low Quality Mesh – the scan almost looks like a photograph in it’s own right.   When orienting around inside the point cloud when you pause it is just like being there.

hires_lowquality_800

Finally we have below the High Density Scan + High Quality Mesh – it is so tightly packed with mesh triangle faces that you can’t read it at the same ‘distance’ as the examples above – I have had to add the red lines in Photoshop so you can make out the shape of the statue plinth and do a close-up.

hires_highquality_800

A model of this density is pretty much un-useable – I have not managed to get 3ds max to even start a render using it’s ART Render Engine – it won’t get off the pre-processing stage.

So a big question therefore is … why bother ?   This is an area in real life of around 25m2 – a model that has 16,300,000 faces in it is berserk.   No computers or VR systems or anything can cope with that.

Just because you can do something it does not mean you should.

The scan therefore should be an aid to producing a manually generated model – and indeed I think that is the case, but there’s not much discussion on this because it sort of bursts the scanning companies ‘bubble’ somewhat.

Next stop for me is to model this scene manually.

This place is ideal for a more detailed comparison of the same area extracted from a low, a medium and a high quality mesh – the scan was at medium density BTW … but it does not seem to matter – the sizes of the triangles are consistent.

Low Quality Mesh first:

polys_lq_from_med-res

Medium Quality Mesh:

polys_mq_from_med-res

High Quality Mesh:

polys_hq_from_med-res

Once you go to the high quality the triangulation becomes more varied/irregular – I think this is dependant on the flatness of the area I selected, here is another version, this time High Quality Mesh from a High Density Scan but the ground here was peppered with rock salt because of the temperature (-3 … I suffer for my art) so there was less flattish areas and therefore possibly a higher triangle count.

polys_hq_from_high-res