The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part Bl. Beijing 2008 
215 
Figure 10. Waveform (solid) and two fitted Gauss components 
(dashed), //j=57> <7 1 =7.3^ 83, (T 2 =7.3. Vertical lines 
show the positions of the echoes extracted by the Gaussian 
decomposition. The EM algorithm performs well in 
decomposing overlapping echo pulses. 
Due to Each waveform consists of the (emitted) start pulse 
waveform of a laser shot for reference. The threshold <7 noise is 
derived on a per shot by calculating the mean of the last 5% of 
the waveform record, (Jj is set to 1. Fig 14 is Pre-processed 
waveform, horizontal lines show the positions of 
threshold a noise . 
In Figure 11, algorithm of SLICER has detected only one 
peak that is ground, but three gauss components have been 
estimated from the waveform by Gaussian decomposition in 
Figure 12. 
4.2 RIEGL 
Riegl waveform data is provided in two files, LWF files 
containing the calibrated waveform sample data, LGC files 
containing the geocoding and indexing information for each 
laser shot. Each waveform consists of a byte array of 
STRTWFLEN (start waveform length) samples representing the 
(emitted) start pulse waveform of a laser shot for reference, 
followed by a byte array or ushort array of WFLEN (waveform 
length) samples representing the surface return waveform. The 
distance from one sample to the next (1 bin) is 0.149855 m. 
such as Fig 13. 
15Ô 
0 20 4-0 60 80 tOO 120 
Fig. 13 Unprocessed waveform of RIEGL 
Fig. 14 Pre-processed waveform 
Three gauss components have been estimated from the 
waveform in Figure 15, Vertical lines show the positions of the 
echoes extracted by the Gaussian decomposition, //j=16.4> 
CT^l.6, JU 2 = 23> <7 2 =1.9> // 3 =35.K <T3 =0.8. 
The performance of the system is to be compared to the 
performance of the EM algorithm. Table 1 summarizes the 
performance of the two detection methods. It is obvious that 
post-processing of registered waveforms yield more information 
than the coordinates that the system outputs. 
Number of 
Point-cloud of 
Point-cloud 
Number of 
echoes per 
gaussian 
of system 
additional 
waveform 
decomposition 
echoes 
1 
2452648 
2469309 
-16661 
2 
426474 
85208 
+341266 
3 
51970 
664 
+51306 
4 
3969 
+3969 
5 
230 
+230 
6 
13 
+13 
7 
1 
+ 1 
2935305 
2555181 
+380124 
Tab.l comparison of the system and Gaussian 
decomposition