**8.1 Augmented reality for indoor heritage sites**

*Advanced Methods and New Materials for Cultural Heritage Preservation*

be visible in the image, which is not constantly possible. Illumination or ambient light problems can impact the extraction process of such points and edges. Active sensors, for example, laser scanners have the ability to avert these restrictions by creating features on the surface using controlled light projection [41]. Many range sensors are produced organised points, in the form of an array or range image, appropriate for automatic modelling. However, texture information or colour can be attached from the scanner using colour channel or from separate digital camera [42, 43]. High-resolution colour textures that obtained from separate digital camera help to create of realistic 3D models. Generally, a single range image is insufficient to cover any object or structure [42]. The amount of necessary images rely on the shape of the object, the amount of self-locking and obstacles and the size of the object compared to the sensor range [41]. In order to wrap each aspect of the object, it is mostly required to perform multiple scans from various locations, which is commensurate to the size and shape of the object and occlusions. The alignment and groups of the various scans can affect the final accuracy of the 3D model, where each scanner has different range of resolution [28]. In addition, this technique can provide accurate and complete details with a high degree of automation for small and medium size objects, which reach the human size [42]. There are two major kinds of range sensors: triangular based and based on the principle of flight time [41]. Triangulation-based sensors are working dependent on project light in a known direction from a known position, as well as measure the direction of the returning light through its detected position. The measurement of accuracy depends on the triangle base relative to its height. Sensors based on the principle of flight time measured the delay between emitting and detecting reflected light on the surface, thus, accuracy does not quickly deteriorate as the range increases [44]. Time-of-flight sensors have the possibility to provide measurements in the kilome-

Image-based rendering used images as modelling and rendering primitives [28]. Image-based rendering uses images directly for creating new views for rendering without explicit geometrical representation. This technique is a significant mechanism for generating of virtual view, where certain objects and under particular camera motions and scene conditions. From the image input, this technique creates a new view of the 3D environment [41]. This technique has the feature of creating realistic virtual environments at speeds independent of scene complexity [42]. Image-based rendering depends on accurately knowing the camera positions to use automatic stereo matching, where the absence of geometry data, requires a major number of carefully spaced images to succeed [42]. Most of image-based rendering correspond to hybrids image-geometry, using means of the equal amount of geometry ranging from per-pixel depth to

Each of indoor and outdoor sites offered many of similar challenges that must be processed to successfully implement AR systems, such as content acquisition [11], content storage and categorisation [46], tracking and calibration [47], marker placement, usability [48] and ergonomic issues [49]. Hence, there are various issues that must be taken into account in order to overcome by special internal or external sites.

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tre range.

**7.3 Image-based rendering**

hundreds of polygons [45].

**8. Augmented reality location**

AR's previous applications for indoor cultural heritage sites have frequently taken the form of "virtual museums". The visitors use AR technology to display objects that may not be accessible to them. This is because the great value or fragility of such objects, or the lack of space inside the museum or the physical object is existing in another museum [36]. One of the main issues that affect the design of AR systems for indoor sites are those of marker placement if using marker-based tracking, as well as ensuring the optimal use of the systems for all age groups and levels of computer literacy. In addition, it is substantial to make sure that hardware used is strong enough in order to support AR applications, and it is structurally robust if being lent to the public.

### **8.2 Augmented reality for outdoor heritage sites**

It can be said that the development of AR systems for outdoor applications is more difficult than indoor applications. Realistic historical buildings in outdoor rendering AR systems require advanced effects such as shadows, lighting and the ability to detect the impact of sky dome illumination on virtual in addition to the real objects [23]. The environment and resources, such as lighting conditions and electrical energy, cannot be as tightly controlled, as well as hardware cannot normally be left outdoors. The use of mobile computer systems in outdoor AR generates several problems such as it is uncomfortable and heavy to wear, and it is very expensive if it is a wearable system combined with an HMD [11] Outdoor AR is a technology of executing augmented reality using outdoor GPS, compass, gyroscope sensor based on augmented reality technology. Unlike to indoor AR, outdoor AR is not subject to spatial restrictions. Indoor AR used a marker to ensure suitable synthesis of virtual object because it happens in relative narrow space, while outdoor AR used location information; it does not use any marker like in indoor system because it happens in relatively wide area [50]. Often the lack of ideal conditions means that marker-based tracking systems cannot be used, leading to rely on other techniques, for example, GPS and inertial sensors, which can be inexact.

One of the key problems that faced to design AR systems for outdoor sites are effectively tracking without using of markers in an environment that may be devoid of features in order to use for tracking. In addition, ensuring that any device used is weather-resistant and vandal-resistant. Furthermore, all the hard-wires that are used must be powerful enough to support AR applications, as with indoor sites. **Figure 6** shows the AR for outdoor cultural heritage **Table 1** shows a comparison between investigated works in AR systems, concentrated on outdoor, indoor, reconstruction and realism.

**Figure 6.** *Augmented reality for outdoor heritage.*

#### *Advanced Methods and New Materials for Cultural Heritage Preservation*


#### **Table 1.**

*A full comparison of different techniques for marker-less augmented reality.*

#### **9. Conclusion**

This chapter has presented the survey of marker-less augmented reality system. In this chapter, we have discussed different techniques related to the augmented reality. An overview on each of them was introduced, identifying the major features and highlighting the main characteristic of each technique. In addition, we have explained in detail the main issues with virtual heritage in augmented reality. We have introduced the key techniques for 3D reconstruction that used in cultural heritage. We have focussed on the main issues of augmented reality for cultural

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**Author details**

and Pisit Praiwattana

provided the original work is properly cited.

\*Address all correspondence to: h.kolivand@ljmu.ac.uk

*Cultural Heritage in Marker-Less Augmented Reality: A Survey*

heritage such as indoor marker-less AR, outdoor marker-less AR, real-time solutions to the tracking problem, real-time registration and cultural heritage in AR. We have presented the research related to these areas and highlighted the main problem

The financial support of this research is provided by KE & I fund from

*DOI: http://dx.doi.org/10.5772/intechopen.80975*

of each research.

**Acknowledgements**

Liverpool John Moores University.

© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

Hoshang Kolivand\*, Abdennour El Rhalibi, Mostafa Tajdini, Sarmad Abdulazeez

Department of Computer, Liverpool John Moores University, Liverpool, UK

heritage such as indoor marker-less AR, outdoor marker-less AR, real-time solutions to the tracking problem, real-time registration and cultural heritage in AR. We have presented the research related to these areas and highlighted the main problem of each research.
