Photogrammetry – 3D scan with just your phone/camera

September 27, 2019 0 By Peter Engel


3D scanning with just your phone? In todays video we’re going to take a look
at photogrammetry Most of us do not have access to high end
3D scanners, they can be quite expensive And they can also be somewhat limited in the
size of the scanned object With photogrammetry all you’re gonna need
is a camera and a reasonably powerful PC Before you start taking pictures, try and
lit the object evenly from all sides and avoid creating hard shadows Circle around the object and try to get pictures
from as many angles as possible Don’t forget to take pictures from top and
bottom as well Do not move the object or it’s surroundings
between shots The photogrammetry software is looking for
features not only on your object, but also in the background, so this would really confuse it This is an example of a decent set of photos
for photogrammetry There are lots of options in terms of software However most of them are either expensive
or very limited in the free version We’ll be using Colmap, it’s available
for all Windows, Mac and Linux For windows and Mac, you can donwload the
pre-built binaries On windows you’ll find two batch files inside
the downloaded archive One tests your machine and confirms, that
everything is ready to run Colmap The other batch file launches the application Prepare 2 folders. One of them should include all your photos
and the other will be used as an output directory In Colmap select Reconstruction – Automatic
reconstruction Set the workspace folder, which is the output directory, and the Image folder, which is the one you just placed all your pictures
in Change the quallity to medium and hit Run This can take a while, especially if you took a lot of pictures Colmap will show you the estimated camera positions and point preview of the tracked object To actually create a printable mesh, we’ll
use Meshlab Import fused.ply file, which you’ll find
in Colmap’s output directory Now you can see all the points that got reconstructed We only want to keep the points on our object, so we’ll delete everything else In our example, the extra points are various contrast features in the room we took the pictures in Use the Select vertexes tool from the main toolbar By holding down the Ctrl key, you can add
to the selection Then click on the Delete vertices in the main toolbar Repeat this process until you’re left with
mostly just the points representing the model to be reconstructed Select Filters – Remeshing – Screened Poisson Surface Reconstruction Change the Reconstruction depth to a value
between 10 to 15 and hit Apply This make take a minute to process You can toggle visibility of objects in the
top right corner with the eye icon This looks pretty rough, so let’s try to
increase the reconstruction depth The higher value you’ll set, the longer
it’s going to take to compute And at some point, usually at values above15, the model won’t get any more detailed This looks much better, we’ll use this model going forward. Here you can see the difference between reconstruction depth 14, 15 and 17 To get rid of the weird shape often generated at the bottom of your scanned object select Filters – Selection – Select faces with edges
longer than. Toggle preview and adjust the Edge threshold value until the vast majority of the faces you want to delete are selected, but all faces
you want to keep are still unselected Then use the delete faces tool from the main toolbar You can also use the select faces tool, which works the same way as the select vertexes tool You can smooth your model with the Laplacian Smooth Smoothing steps between 8-20 usually work well Be aware that too much smoothing will remove valuable detail from your model We are now ready to export the mesh Use PLY or 3DS if you want to keep the texture, for example for publishing the file online Or STL if you really want to save just the
geometry of the model Doing photogrammetry with glossy objects is tricky Glossy surfaces will change in appearance as you circle around the object You can easily prevent this from happening with painters tape, which will add detail and created matte textured look Here you can see the difference this made on the reconstruction The same applies to transparent objects, like glass Spray it with chalk spray or cover it up with painters tape, otherwise the reconstruction won’t succeed Statues are perfect for photogrammetry Their surface is rough and won’t cast any
reflections They have a lot of tiny features to be tracked and reconstruced Your model will amost always end up with a hole on the bottom But that’s very easy to fix in for example
Meshmixer And in this case, it’s even better to just
cut the stand and create a perfect surface to be placed on the print bed Check our older tutorials to learn how to these edits in Meshmixer Now you’re ready to slice and print
your reconstructed model