International Archives of the Photogrammetry, Remote S ensing and Spatial Information Sciences, Vol XXXV , Part B2. Istanbul 2004
Interna
as well, and not only on the ground pixel size (which is often hours c
used wrongly as synonymous to image resolution and image running
quality). | configu
| process
Table 2 also shows that all quality measures are gradually | large u
deteriorating with decreasing pixel size. One cause for less | km ofr
completeness is that paths in fields are only partially extracted |
because the path surface is blurred and road edges are very 4.2 Gi
weak (Fig. 6), while in small villages performance was also
worse (Fig. 7). However, the quality deterioration is much less Our sy
than the pixel size reduction. E.g. for 60-cm vs. 20-cm pixel (Swissi
size, in the first case we have 9 times less data, but Howev
completeness, correctness and accuracy deteriorate only by HRS d
i : 7.5%, 4.5% and 40%. On the other hand, this slight quality | image,
Figure 3. Examples of road extraction and junction generation decrease may still mean expensive additional manual editing, so narrow,
in scenes with small settlements. the question of pixel size choice should be carefully considered. i Sys
e inc
Quality measures | Aerial | Aerial | Aerial | ADS40 visible
20cm | 50cm 60cm 30cm edges 2
Completeness (%) |95.44 [90.49 |8828 95.27 compar
Correctness (%) [94.65 |92.53 190.68 19424 comple
Length of 42.08 [42.08 [42.08 42.08 rem
reference (km) Qu:
Length of 4243 |41.15 140.97 42.54 | meas
extraction (km) [Compl
RMSemor | x [045 [0.60 [0.72 1.00 onan
(m) y (0.43 0.61 0.75 0.97 Length
Mean error x [0.04 0.17 0.29 0.57 peterenr
(m) y [008 [0.22 1019 0.44 Length
Processing time (s) | 1872 |774 |620 1184 exten
RMS
Table 2. Quality evaluation of the results in Thun site. error (mn
3 id] Mean
Figure 4. Examples of road extraction and junction generation error (n
in scenes with small settlements. Proces:
Tab
It is ap
depend
Figure 6. A path extracted in 20-cm pixel size image (a), but too, an
only partially extracted in 60-cm pixel size image (b). within
The black lines are the extracted results and the white influenc
lines are the reference data. conditio
much le
to airbo
| object d
is simil:
| than In
caused
coordin:
ic | 8 system.
Figure 5. Results in a scene with a first-class road. | is simil:
Figure 7. A village road extracted in 20-cm pixel size image (a), | HRS oi
Our system delivers the best results with the 20-cm orthoimage. but not in 60-cm pixel size image (b). The black lines | DSM/D
About 95% of the roads are correctly extracted with an are the extracted results and the white lines are the | 8 shows
accuracy of about 50 cm. The non-extracted or falsely extracted reference data. from the
roads are mainly in small villages. Taking into account the = = |
discrepancy between the ADS40 and the 20-cm film Table 2 shows that the processing speed of our system is high In the (
orthoimage (as indicated by the large mean values), our system (e.g. ca. 30 minutes for more than 40-km roads in 20-cm pixel inside t!
performed equally well on ADS40 data. Indeed, visual check size images), and that processing time decreases almost 1:1 are class
over the whole test site shows that the results from ADS40 data With orthoimage pixel size. The processing time also depends those in
ADS40 are sharper and have a better radiometric quality scene, increasing with them. Extensive tests at swisstopo with fields is
compared to scanned film. Image quality is important in general 50-cm orthoimages show that roads In an average road density false exi
and for object extraction, and depends on such image properties [:25,000 map sheet covering 210 km? can be extracted in 3-4 from th
744
|
2 % - > ro: densi accer extent o0 ov iv he | us C
are actually at the road centers. Furthermore, images from on the road density and to a lesser extent complexity of the | Fig. 90