Avoiding Cones in iModeller 3D

This page shows how to avoid "cones" on top of objects.

Origin

"Cones" on objects are a common problem people encounter when using iModeller. They stem from the fact that iModeller does not have a silhouette which "cuts off" the specific part of the object.

One can see this in above image - two cameras observe an object, but the silhouettes they get from the object don´t help determine the object´s boundaries at all - one can see a cone already!

Solution

Since iModeller bases on silhouette cuts, it is important to capture the relevant silhouettes - otherwise you end up with a hat. When you raise the object from the ground, you end up with another ´hat´ on the downside.

You can easily create artificial views of the object when using the ´generate image´ button in the 3d view - generate an image and "unmask" those parts that are not captured by any other image. Create a view from the side of the object, then unmask the cone-top. iModeller then recreates the shape without the cone.

As a practical solution, and especially if you have lots of objects to scan, it might be wise to set up a static environment for your objects: (see image below)

• place the object on a post. let the camera be about 2 times as far away from the closest calibration point as the post is high.
• make sure that the camera position is not lower than thirty degrees with respect to the center of the calibration pattern, and not higher than 60 degrees.
• you need two different heights for the camera tripod to capture both flat tops, when the object is on a post.
• make sure that each position of the camera has one line of sight aligned to the top or bottom of the object, respectively.
• This might seem a bit complicated, but it will help you to quickly capture the objects you desire. Just imagine that the computer ´sees´ only the silhouettes - it does not know about flat tops of e.g. cans. To tell the computer of a flat top, make sure the silhouette it gets captures this fact.

Please note that iModeller does not recreate ´depth´, i.e. it cannot detect concavities. Therefore, any textured part of the object which originally depicts a concave area (e.g. a top view of the spout of a vase) must be distorted. To overcome this, take a picture directly from above this area and use the ´Use for Texture´ mask on the relevant area in this image.