OVERVIEW OF PASSIVE MARKERS

Four marker types we researched are presented in ascending order of information contained by the marker.

Using the embedded webcam on a 2010 MacBook Pro, the markers were detected from 2 - 10 feet while moving, rotating, and in various states of corruption. As predicted the markers could be detected while being moved or drawn on. The markers could not be detected if the vandalism occurred on the edges enough to disrupt the sharp corners of the frame. One marker was also successfully turned into another maker by filling in the squares of the pattern with pen the same color of the marker.

Another set of tests using 5 inch markers in the even-lighting condition of the Health and Sciences library found that the markers could be seen from 30 feet away if the background behind the marker was static. Using the same set of markers inside a darker and less evenly lit condition, we could not reliably find the markers from more than 8 ft away. Therefore, there seems to be a large variability in detection when the white border is disturbed, the lighting uneven, or when possible shadows or glare effect the detection of the contrasted edge of the marker.

note:
*QualcomVuforia comes standard with 512 unique markers.
*TheARToolkit Pattern Maker tool purports to make an almost infinite unique series of markers that can be imported as training data into recognition/detectionsoftware. (Note: this implementation has not been tested on mobile devices and we have only been able to find pc detection software so far, though it’s probably just a matter of no one having a need yet.


QR Codes

We did a small set of tests on QR codes of varying sizes and data densities. We tested 150 character and 4 character QR codes that were displayed on a laptop monitor at 3.5” square. The four-character code could be scanned successfully and reliably from 4.5’ using an iPhone 3gs and Qrafter software. The 150 character code could be scanned successfully and reliably from 2’ using an iPhone 3gs and Qrafter Software.

The higher density of the 150 character code required that each square that comprises the code be smaller. This causes the cell phone camera to lose focus at a greater distance as the resolution remains constant.

We also tested a small, high density 1” square, 991 character, 157 word QR code that could be read from 2.5” away. This small size, high density, and close distance all made reading this marker difficult. It was read successfully, but not reliably when the camera was in approximately the same spot. Increasing the size of the marker would, by relationship to the focal length of the camera, increase the distance the marker is viewed at.

This is just above the minimum focus distance of the iPhone3gs camera. All of these tests required that the phone be held still and close to parallel with the QR code marker.

DISCUSSION AND DESIGN GUIDELINES
Designing with Image Based Markers

Detecting image based markers requires a set of feature data to be loaded as they are specific to individual unique images, and determining the physical location of the markers (angle, rotation, distance) requires longer processing time and a clearer image. This necessitates a better camera and more powerful mobile device.

Image based markers provide a way to create markers that are meaningful even to sighted users or users without a mobile device. There are guidelines and rules for creating image markers that will work reliably. They take more time to process and better cameras to identify so newer devices would be needed. They also take large amounts of memory and so a limited set can be stored to identify without going online and getting a new set of data.

Because of these limitations, a system using image based markers for room signage might work better as a room classification system.

Designing for Reliability

To build a marker based signage system that works reliably, multiple types of markers could be used together to provide varying densities of information that would work reliably from different distances. The inclusion of color-based markers could work well for identifying potential locations where more information would be located.

A specific color can be tracked even while moving a mobile device very quickly as the color is not distorted by the motion of the camera. These color markers could alert the user that a room sign has been spotted. If all color markers are a specific size then that size can be used to make an estimate for distance or relative distance from other markers.

The color marker could be used in conjunction with binary or QR code based markers. The binary marker could also be at multiple scales, repeating within itself so that it can be viewed from far away or close up to receive the specific room number. Finally, a QR code could provide more information.

A unique configuration of bright colors of a color-based marker is not only reliably tracked by a mobile device, but are also easy markers to spot with the naked eye. The strong contrasts makes wayfinding for those without a mobile device still easier, particularly for a visually impaired individual. In our prototype we used two shapes of contrasting colors that used to eliminate false positives. There was still some false positives and misses because of variable lighting levels. Research conducted at Smith-Kettlewell Eye Research Institute proposed a color marker system using relative lighting variances in multiple colors to produce a robust and fast detection algorithm. Their marker system does no shape tracking so it is very fast as it is only color based. (Coughlan, Manduchi & Shen, 2006).  Another study by Manduchi, Coughlan & Ivanchenko on a camera phone wayfinding system showed that visually impaired users were able to reliably find color markers (2008).

Designing for a Dynamic Database

This implementation requires a central database and some organized authority to create the database, host the information, and facilitate information input and update.

Using a binary marker system, building users would be required to input their current location explicitly stating what building they are in. The building can be selected from a list of recognized buildings that relate to their current GPS or IP address location or obtained from QRcodes located on the building exterior.

By entering a current building, a limited set of binary markers can be used to identify different rooms in different buildings. This allows the same marker to be used in two buildings but when accessing the database it can pull out different information to present to the user regarding the specific room they are looking at.

Designing for Dynamic User Generated Content

This implementation would require individual room users to generate all content. The QR codes are easy to create using free software.

A binary marker system can be used to identify room number and set of user generated web pages or relevant room data. This system could work by requiring the user to photograph/scan a QR code that is generated by the users of the room. QR codes can hold web pages or just vanilla text data. The binary markers could then be used to identify what rooms are currently visible to the user's mobile device. Then, the user could move closer to the desired room and scan the QR code for that room. One possibility in facilitating locating the QR code is using a slot built into the sign that would place the mobile device into the correct location to scan the code.

 

 

Signage Prototypes
The two types of signage we used and the size of each marker and information they provide were determined based on our research findings discussed above.  Only a rough idea for laying out the markers was needed to test for reliability.  Material and other design considerations for the signage itself need to be developed further.

Smartphone Wayfinding App