Fun with SFM – Part I: taking pictures

So, welcome to our first tutorial on SFM – structure from motion to get a 3D model of your favourite object. In our case, due to our name “Epigrammetry” which combines Epigraphy and Photogrammetry, we would like to start with a stone. Actually not just a stone, it is one side of a sarcophagus placed outside the church of San Canzian d’Isonzo in Italy. I choose this example because I do not need any permission for taking pictures there – and using those pictures for our turorials online.

If you would like to follow our instructions and you have choosen a certain object for it, please always make sure that you are allowed to take pictures and to use them. In most cases, you are allowed to photograph objects, but you are not allowed to show your results online or to publish them, so this is the tricky thing you have to be aware of.

In this first part we will concentrate on taking pictures for your model. You will not need a high professional camera – use your smartphone, because this is enough to start with the basics and getting a feeling of the process.

1. The light – when taking pictures, always consider the light!
Is it sunny, is it cloudy, has your object any shining surfaces? For 3D modelling, all this things are important.
The best weather – if your object is placed outside, like mine is – is actually a cloudy day. The light will be consistent on your object and this will give you the best results, especially if considering the texture (the colours of your real object that you want also on your model). If there are some too dark spots, your camera may not be able to handle them, so it is lost for the software, because you cannot get any points out of it.

2. Keep about the same distance to your object – at least try! I know, this can be sometimes really difficult, but your results will be better. Also, try to keep exposure and focal length the same while taking your pics. And you will have to do a lot of them. For our example here, I took about 70, which is okay for a very rough model, but a quite good one.

3. Move! You have to move the camera. By this, I mean you have to take your pics step by step. Always let about 60% to 80% of your pics overlap and never stand still an just turn the camera in different directions. At least, if you annot move your feet, move your torso and the camera to another position. Yes, this can be very funny for your spectators. 😉
So, just keep in mind: Overlapping and moving!

3a. If you have a small object and you want to get every side, never move the object! It won’t work! You will confuse the software. If you have to move the object, you have to do different models of every side and then you have to bring them together with the help of Meshlab or whatever program you want to use.

4. Try to get every pic of your object out of at least three positions. Help yourself by following the surface of your object with your movements – at least, this works out for me and the stone reliefs. For a frontal and flat object, try to take pics from different positions and angles.

5. Keep a list. If you have to take a lot of pics for different models, keep a list of your pictures by writing down their numbers in line, the object, the side, the date. You will definitely get confused, trust me. 😉

6. Always do a back-up. And yes, please, save your data immediately! Do a back-up. You know why. 🙂

Of course there are other very good tutorials on photogrammetry 101 on the Internet and I myself learned a lot by reading and watching them.

We will catch up with our little project when I am back from my holiday!

Stay fierce!

Astrid


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