# Fast and High Precise Spatial Documentation of Traffic Accident Site Using Only Low-Cost RPAS
## 4 Discussion  
The utilization of RPAS for traffic accident site documentation could rapidly speed up the whole process. Arranged traffic accident documentation using RPAS took seven minutes, including the time for RPAS preparation and site reconnaissance. Documentation of a real traffic accident depicted in Figure 1 took 60 min [11]. These two examples of traffic accidents are comparable, meaning acceleration is higher than eight times. In addition, unlike the handmade sketch, the model preserves the whole reality. The model formed from the RPAS data can provide better data reusability than sketches and photos taken conventionally at the accident site. The model preserves all information in one complex and coherent dataset. The accuracy of the model is in centimeters, as opposed to the decimeters accuracy of the handmade sketch. The subsequent processing of the images took only minutes, not hours, as in the case of a conventionally created plan. The sketches need to be redrawn into plans using computers, which means the traffic officer has to execute the same work twice. To conclude, the utilization of RPAS makes the whole process of traffic accident documentation faster, more precise, and time effective. Moreover, utilizing this method is safer for traffic officers, since they do not have to move unnecessarily close to the traffic accident site on the road or highway. There is definitely a need to make the whole process faster. Replacement of conventional methods for RPAS could save more than 85% of the time. Reducing traffic accident documentation from one hour to seven minutes could save more than $127,000 in situations where the highway must be closed in the Czech Republic, for instance. This cost comes out from [10] and includes indirect costs caused by the closed highway. To evaluate the efficiency of this proof of concept, we compared a few studies to our own study, evaluating major parameters like root mean square error (RMSE), using/not using GCPs, flight time, overlaps of images, etc. The authors of [7] used two techniques for data acquisition (waypoints and points of interest). RMSE was 43 mm and 59 mm, respectively, flight height was approx. 15 m, and four GCPs were used for georeferencing. The authors of [6] tested the utilization of RPAS in the weather conditions of Kuwait, where a few flights were done. The flight with similar parameters (flight height of approx. 17 m, overlaps 80/75%) reported an RMSE of 85.2 mm. The flight time was approx. 8.5 min. The authors of [2] also conducted a few flights. A comparable flight (flight height of approx. 10 m) reported an RMSE of 10 mm or worse (lower tens of mm). The flight time was approx. 4.8 min, while the processing time of 76 images was 30.3 min. The authors of [4] tried to figure out the best overlap setting. The lowest reached RMSE was 170 mm, with a similar overlap (frontal overlap 75%). The flight height was 65 m and three GCPs were used. The authors of [3] concluded that usage of advanced methods (geodetic total station, photographic rectification or RPAS) can save around 50% of the time necessary to create the traffic accident documentation, compared to conventional methods. The average \begin{table}
\begin{tabular}{c c c} \hline \hline
**Reference Object No.:** & **Real Object Dimension (mm):** & **Object Dimension in Model (mm):** \\ \hline
1 & 300 \(\times\) 300 & 302 \(\times\) 301 \\
2 & 490 \(\times\) 399 & 493 \(\times\) 399 \\
3 & 400 \(\times\) 370 & 401 \(\times\) 373 \\
4 & 400 \(\times\) 370 & 402 \(\times\) 371 \\
8 & 103 & 105 \\
**Distances between objects:** & **Real distance [mm]:** & **Distance in model [mm]:** \\
5 \(\rightarrow\) 7 & 10,433 */10,433 ** & 10,500 \\
5 \(\rightarrow\) 6 & 5482 */5450 ** & 5470 \\
6 \(\rightarrow\) 7 & 6031 */6120 ** & 6040 \\ \hline \hline \end{tabular}  
* Measured using *laser rangefinder, ** steel tapeline.  
\end{table} 
Table 3: Differences between reference objects dimensions (reality vs. model). measurement error is generally approx. 5.3%. Our study had a flight height of approx.