Practical comparative evaluation of an integrated hybrid sensor based on Photogrammetry
and Laser Scanning for Architectural Representation
€ Balletti*. F. Guerra*, P. Vemier*,
N. Studnicka**, J. Riegl**, S. Orlandini***
* Laboratorio di fotogrammetria - CIRCE
IUAV Università degli Studi — S. Croce 1624 — 30135 Venice - Italy
**RIEGL LMS Gmbh
***Microgeo S.r.l.
KEY WORDS: Photogrammetry, Architecture, Integration, Modelling, Laser scanner, Orthoimage, Multi-scale
ABSTRACT:
In architectural surveying aimed to restoration and to conservation, close to the traditional two-dimensional vectorial representation
in orthogonal projection, raster representation has gained considerable importance. Among all raster representations, the most
widely-used is the digital orthophoto.
The application of laser scanners as a new instrument for terrestrial survey together with firmly attached, high resolution and close
range calibrated digital cameras, has permitted to obtain in straightforward way not only orthophotos but even to produce more
sophisticated elaborations such as 3D orthophoto or solid image. These representations allow to get a vector representations via
digitalizing in a single image.
In the paper we will describe in detail a survey procedure that is based on an integrated photogrammetric — laser scanning system
manufactured and marketed by Riegl LMS GmbH (high performance 3D imaging laser sensor + high resolution digital camera). A
newly developed software allows to automatically extracted 3D orthophoto and so-called “solid images” from the hybrid data set
(registered scan data and digital images) which can be subsequently used to easily create vector drawings by means of 2.5D
digitalizing.
This procedure is considered as an alternative approach to traditional digital close range photogrammetry, usually carried out in the
activities of the photogrammetric laboratory of CIRCE — IUAV, to produce the well-known final representations: vectorial drawings
and orthophoto.
Considering that these products are in Italy the ordinary requests of a survey final user, such as architects or more generally
restoration technicians, the authors have done a comparison not only on the achievable accuracy but also on time, costs and resources
consumption that are necessary in real applications following the two procedures: the classical one based on traditional
photogrammetry, and the new hybrid system approach based on photogrammetry -laser scanner integrated system.
As test field the Arena of Verona has been chosen, such as significant application for the comparison just for the big amount of data
collected by the photogrammetric laboratory of CIRCE during the photogrammetric survey campaigns (still in progress), and
moreover for its own characteristics of an archaeological and architectural survey combination.
The objective of the research is to offer the possibility to a surveyor to choose the best solution for representations productions,
demanded by architects, restorers, etc., considering both accuracy and representation requests.
Introduction The essential point is that while photogrammetric survey of a
monument such as the Arena is a completely controlled
Can laser-scanner survey be an alternative to topographical- technique, for which the times, costs and obtainable results are
photogrammetrical survey? known, laser-scanning has been applied only experimentally
If not, how much and to what extent can this new methodology and there is no case theory so generalized to be able to
replace or bolster the "old" method? effectively design a survey whose instrumental support is based
To answer these queries, we tried to understand if the hardware on the 3D scanner.
and software available today for laser-scanning can obtain a To be able to accurately compare only the scanning and
satisfactory result according to the current canons of rectification techniques, we decided to keep the topographic
architectonic representation, which calls for not only the use of reference system common, made up of topographical local
vectorial drawings in orthogonal projections but also raster system and detail nets.
images and 3D models.
It was decided to carry out the survey of a single object by using
the two different methods and compare them in each individual
phase. The test area was a portion of the exterior facade of the
Arena of Verona, consisting of three arcovoli (archways) on the
south side: the XXXI, the XXXII and the XXXIII which
represent an area functional to topographical-photogrammetrical
survey. It was a test area significant in terms of dimensions in
order to not oversimplify the problems while still maintaining
complete control over the procedures.
The purpose was to evaluate the techniques from an operating
perspective and therefore there is the need to keep closely to the
operating and professional practice of survey.
We analysed the operating methods of the two methodologies
on the field and the procedures for controlling and handling the
data in the laboratory, highlighting the procedures common to
both techniques, the ones logically similar and those that are
completely different.
We then compared the vector and raster representations
obtained, to evaluate the differences in the results and attempt to
identify the causes of the differences.
Finally, we evaluated the resources (times and costs) necessary
for carrying out the survey using both techniques, to highlight
any economies made possible by the use of laser scanner
methods.
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