Imperia: Modeling a Moving Object

A project log for Photogrammetry and Image Acquisition

An exploration into image acquisition techniques and its effects on the quality of 3D models using Pix4D Mapper Pro software.

travis-broadhurstTravis Broadhurst 07/11/2016 at 11:270 Comments

Imperia is a statue in Konstanz, Germany in the town harbor. It was built in the 1990s to commemorate Konstanz as a popular town in Germany for past German kings and as the location of the only Council of the Catholic Church that occurred outside of the Vatican. The statue rotates on it's base once every 4 minutes 24 hours a day and 7 days a week, is 9 meters tall, and is situated on a background of the Bodensee (water) and sky. These all combine to make it a difficult, if not impossible object to model. However, it is of considerable interest as it is the symbol of Konstanz and a 3D model could be very beneficial for historical preservation in the case of floods (which happen every year).

The model is difficult due to the rotation and background. If the object is moving relative to its surroundings, then any keypoints detected on the object relative to keypoints on the background will be invalidated in the next image since the same keypoints on the image could be at a different position relative to the background. To make matters worse, the background is composed of sky and water, both of which are reflective surfaces and have a low number of keypoints. If the number of keypoints is low, the number of matches will also be low the the model will be inaccurate.

In order to model Imperia, I first tried using images captured during drone flight around the object. I carefully chose images to try to get the statue in the same rotational position but with the drone in at a different angle around the statue. Although these Oblique photos would normally produce a decent model, these images did not calibrate due to the low number of keypoints since the majority of the background was water and sky.

The next attempt that is currently in process is to fabricate a background for the statue and use image editing software (GIMP) to edit the photos. There is a rotunda in a cathederal in Konstanz that has a circular wall. I have created a model of this wall, and have taken images of Imperia at different angles. I have also edited the images of Imperia to make the background transparent. My next plan is to use Blender to take screenshots of the mesh of the wall of the rotunda every 10 degrees. I will then superimpose the images of Imperia (also taken every 10 degrees of her rotation) on the images of the wall to create the images as if Imperia were in the rotunda and not at the harbor. This has taken a great deal of trigonometric and optical calculations to ensure that the scaling of Imperia is accurate and that enough of the background is included in the FOV of the camera. I hope that this effort will prove fruitful, and will keep this project log updated.

I have uploaded a video file of the altar at the center of the rotunda, but will also upload images of Imperia and the mesh of the wall of the rotunda with the tag "Imperia_"

Thank you.