Tracking Configuration

Introduction

This chapter will explain how to configure markerless tracking and gives some tipps on how to improve tracking quality. Taking care of e.g. measuring the size correct size of the printout will result in a stable tracking and augmentation.

Pre-Print

• Resolution of image may have very high resolution, e.g. 3000x2000 pixel to allow high quality printing
• Rescale the image to have a resolution of e.g. 300x200 pixels or 450x300 for landscape (keeping the aspect ratio fixed)

Printing

• Make sure to measure the same format (landscape/portrait) like the digital version
• Make sure the printer has printed out the whole image i.e.: no missing parts
• Print the image on diffuse and non-reflective material

Measuring the print-out

• Verify the aspect ratio
• The ratio width/height of digital image should be equal to width/height of printed image
• e.g. 300px/200px = 1.5 <=> 333mm/222mm = 1.5 and e.g. 200px/100px = 2.0 <=> 222mm/111mm = 2.0

Difference between Tracking initalization (Localization), Interframe tracking and detection

The tracking approach implemented in Unifeye consists of two main components:

Tracking Initialization (Localization): This step is the crucial entry point for the tracking and determines the first initial value for the tracking by detecting the configured reference image without any prior information. The step is needed when starting the markerless tracking and in case the tracking loses its reference.

Interframe Tracking (tracking from frame to frame): Given an initial value from the initialization phase, the tracking can then compute further information based on the previous one.

Detection in comparision to tracking does not compute a pose. It can be helpful, if you are only interested in finding out, which picture is beeing shown e.g. for a card game. It is not possible to augment something perspectivly correct, because there is no pose computed.

When tracking works best

The tracking works well if the user is having the target printed on a diffuse and non-reflective paper or material and lying on a flat surface. The lighting conditions should be simple: bright, diffuse and non-direct light. The user is having a large part of the target image in the camera field of view and the viewing angle is not steep.

Markerless Tipps

• Use diffuse paper for printout, reflections influence the tracking
• The best resoution have a minimal resolution in x or y of 200 or 300. For example 200x224, 332x200, 200x300, 300x200, 225x200 are all good resolution for markerless
• Select an almost squared region, e.g. not 1:4 better 1:1 or 3:4 for x:y

• Use the digital version of the target and if needed, take the reference image with the device camera that is going to be used, e.g. iPhone. Take this image straight from above

• Select a region which is a little bit smaller than the pre-print version

Selecting a good target

Sometimes hard to decide for a human, which targets are good, but here are some general findings. Photos are in general very good. Targets which are not well suited for markerless tracking are

• Little visual details
• Text
• Pictograms with high black/white contrast
• => Each target should be tested first with the "Fast" version of the tracking, then with the "Robust" version of the tracking

-- SupportMetaio - 2011-12-07