APPLYING UNMANNED AIRSHIP TO RAPID DETECTION 
OF URBAN BUILDING CHANGES 
Xiaodong PENG ab ’*, Zhaoqin LIU b , Jinkuan YIN b , Yongrong LI b 
d Remote Sensing Information Engineering of Wuhan University - xiao_dong_p@163.com 
b Chinese Academy of Surveying and Mapping, No 16 Bei tai ping Road, Beijing, China( 100039) 
KEY WORDS: Digital Photogrammetry, Change Detection, Aerial Photogrammetry, Buildings, Unmanned Aerial Vehicle, 
Auto-Aerial Triangulation 
ABSTRACT: 
In order to supervise and manage building change in urban development, unmanned airship is recommended for building change. 
With the unmanned airship, lower flying height can be obtained. As a result, high resolution aerial image can be acquired. And then, 
auto-aerial triangulation are easily applied to images so that product efficiency is greatly improved. And also, DSMs can also be 
quickly get. Width DSMs from different times in short period, building changes can be figured out by differential between DSMs. 
1. INTRODUCTION 
In the development course of urban, it is inevitable to face 
constructing new town and reforming old city region. Often, 
there are some buildings which appear illegally and block the 
normal process of city project. For example, the buildings 
constmcted without license aimed at more compensation may 
appear at the reforming time. In order to supervise and manage 
these illegal buildings, especially for supervising constructing 
and tearing down buildings, the authorities need to know how 
things are going in the work area in every stage of the project. 
This means that the authorities need repeating survey the little 
region periodically, perhaps biweekly. 
Building change doesn’t means only construction of new 
buildings and tearing down old buildings, but also includes 
adding and removing floors from existing buildings. It is 
impossible to send a group of people to work around to record 
every height changes of city buildings by filling tables. Because 
nobody knows which building will be changed at next stage, 
then the conservative way and only way is to recording every 
building’s state at each stage. It is a too burdensome work that it 
is unfeasible. As to DLG, it is not fit for recording Z data, say 
anything of that all building’s data should be recorded in every 
survey. So DSM is preferred to be chosen. Then the building 
changes can be marked after computing difference of DSMs of 
different stages. If the DSM comes from photo, there are more 
detailed and intuitionistic information that can be shown. 
In this paper, the reason why unmanned airship should be used 
in supervising building change will be depicted. Then things 
done in fieldwork and indoor work are specified. Especially, 
auto-aerial triangulation is paid more attention, for it is very 
important in fast aerial photogrammetry. 
2. RECOMMENDED WORK PLATFORM 
For litter region, ground survey can get detailed information and 
reach high accuracy and precision. But it is expensive, and most 
worse it is inefficient. It can not accomplish mapping and 
recording building changes in a few days. Conventional air 
photogrammetry is also not fit for litter area and short period 
repeating survey. As to remote sensing, there should be a 
special satellite focus on the little region statically for long time 
which is wasteful. In this case, unmanned aerial vehicle may be 
a good choice, for its simple mode of taking off and landing, 
relative safety, and ability of low fly height. And considering 
photographing on the urban, unmanned airship is preferred for 
its more security, which is also a kind unmanned air vehicle. 
Unmanned airship doesn’t need large area of even ground for 
taking off and landing. Hundreds of square meters’ playground 
or grass lawn is enough, or even a section of straight road of one 
hundred meters is also OK. For the whole surveying region 
would be surveyed repeatedly, for example, once a week or 
twice a month, thus the airship does not need inflation and 
deflation at each survey, but just on inflation at first time and 
one deflation at last time. Unmanned airship can fly at a height 
of nearly 3 kilometers, but also can fly at a low height of a few 
dozen meters. For large scale surveying and mapping, the fly 
height is always restricted lower then one kilometer. Then you 
can see unmanned air ship can fly very low to get high precision 
images in accord with project demands, and sometimes, can 
participate in close range photogrammetry. 
3. FIELDWORK 
The sensor should be discussed in some extent at first. 
Generally, professional aerial photogrammetryic cameral should 
be used in aerial photogrammetry. At present, general digital 
cameral also can be applied to aerial photogrammetry if it is 
rectified in advance. By comparison, general digital cameral is 
cheaper, lighter, easier to access. It is much more fit for 
assembled in unmanned airship. 
Unmanned aerial vehicle is usually unstable when fly in the 
windy condition. This cause the camera assembled in the 
unmanned airship to be unstable, that means that the principle 
axis of cameral would depart from perpendicularity to far and 
direct to orther direction arbitrarily. To avoid this, two-axis or 
three-axis stabilizator should be recommended. When taking 
photos in the air, the camera is assembled in stabilizator which 
should be designed to keep the cameral posture angle restricted 
within 5 degrees or so. The Figure 1 shows a picture of airship.