EuroSDR Projects - Host Ireland

3.1.4.9 Delft University of Technology
The level of automation was considered medium. There are many automatic steps in the processing
strategy (see Table 3-2), but an operator is needed to guide the extraction process and for quality
control.
3.1.4.10 University of Aalborg
In the applied method the building ground plans are needed, and if they are not available, they have to
be created manually. The level of automation in building extraction is high, but some operator
involvement was needed as the procedures were at the development stage. Some of them were tested
for the first time.
3.1.4.11 Dresden University of Technology
In the Dresden method the building polygons are needed. If ground plans or such are not available,
they have to be created manually. After this point cloud extraction can be performed automatically
with a batch algorithm in e.g. ArcGIS. The user has to define the mean point spacing and the accuracy
of the laser scanner data. Then, the whole building model reconstruction runs automatically. One by
one, it reads the point clouds and processes them.
3.2 Accuracy Evaluation
3.2.1 Analysis Using Reference Points
Reference points were used to analyze the accuracy of the location (single point measurement), length
(distance between two points) and roof inclination (slope between two points) of the modelled
buildings. Single points were analyzed separately for planimetric and height errors. If a DEM was
included, building heights were measured to the DEM using bi-linear interpolation. If not, wall
vectors were used. On some models the same ground height was used for whole buildings resulting in
large errors in building height determination. These cases were marked at the building height analysis
stage.
Root mean squared error (abbreviated to RMSE, Equation 3-1), was calculated for building length,
height and roof inclination.
42
RMSE =
n
i=
1
( e − e )
1i
n
2
2i
(Equation 3-1)
where e1i is the result obtained with the described retrieved model, e2i is the corresponding reference
measured value, and n is the number of samples. Additionally, minimum, maximum, medium, mean,
standard deviation and interquartile range (IQR, Equation 3-2) values were calculated. Interquartile
range values represent the range between the 25 th and 75 th quartiles.
IQR p75th
p25th
−
= (Equation 3-2)