3D Mobile Mapping Surveying For Road Condition
government to collect the road condition data. With road condition data, government can monitor and fix damaged road. But currently, road condition data has not been updated, because inventory of road data is time consuming and take a long time.
Based on that problem, it needs method for collect road condition data faster and meet the specified accuracy standard. One of the method for road condition data problem is Mobile Mapping System (MMS). MMS is one surveying method that use laser scanning that is attached in top of car. As the car moves, laser scanning scans the road and its surroundings [4].
1.2 Component of MMS
MMS uses Topcon IP-S3 HD1 as research instrument and consist of two main components, hardware component and software component. Hardware component consists of Global Navigation Satellite System (GNSS), Inertial Measurement Unit (IMU), laser scanner, wheel encoder, digital camera, timing box, indicator box and IP-S3 Cube [6]. Software component consists of mobile master field and mobile master office. Those two components is shown in Figure 1.
Figure 1 Component of MMS [Topcon X]
1.2.1 Hardware Component
Hardware component is whole part of physically form of Topcon IP-S3 HD1.
Each part of the component has its function. Topcon IP-S3 HD1 is shown in Figure 2.
Figure 2 Topcon IP-S3 HD1 [6]
Topcon IP-S3 HD1 consists of seven parts that integrated to obtain point clouds [6]. Those seven parts are:
1) Global Navigation Satellite System (GNSS)
GNSS is a positioning technology and Topcon IP-S3 HD1 uses Global Positioning System (GPS) from United States and Globalnaya Navigatsionnaya Sputni Kovaya Sistema (GLONASS) from Russia. The principle of GNSS measurement of MMS is that the position of the vehicle (rover) is determined relative to the base station so that the configuration can produce corrections for some error sources that occur during the GNSS measurement so that the resulting position data is more accurate [Abidin X].
2) Inertial Measurement Unit (IMU)
IMU is integrated system of accelerometers, gyroscopes, and a set of computers that can calculate speed transformations and several other mechanisms for determining position information, attitudes and speed. The function of accelerometer is to detect vehicle speed and gravity acceleration.
Gyroscope is used to detect angular change [4].
3) Laser scanner
Laser scanner has two types measurements. First is distance and second is angle. Distance measurements on MMS uses pulse-based or time of flying (TOF). TOF records the travel time of laser waves when emitted until received back by the laser receiver which then travel time will be used to calculate the distance between the laser scanner with the object [3]. In angular measurements, MMS uses angular encoders that serve to measure the vertical angles and horizontal angles of the incident light on the laser scanner against the point of the object. Topcon IP-S3 HD1 has density point at 700.000 dots per second, vertical viewing angle at 30°, horizontal viewing angle at 360°, and can reach object maximum at 100 m [6]. Laser scanners on MMS utilize laser light technology that is used to scan objects on the surface of the earth.
The results obtained using a laser scanner are a set of points (points clouds) that have three-dimensional coordinates with a particular coordinate system with additional information in the form of reflectivity value of the scanned object [3].
4) Wheel encoder
Wheel encoder is used to determinate vehicle speed with calculate wheel rotation and duration for one wheel rotating. In MMS, wheel encoder is attached on the car rim. The calculation of speed is used to correct instrument position [4].
5) Digital camera
To get color of point clouds, MMS uses spherical digital camera with panoramic mode [9]. There are six camera sensors to capture photo of object at the same time. This camera has 30 megapixels’ resolution and 10 fps in shutter speed.
6) Timing box
Timing box is a part that used to connect laser scanner, camera, GNSS, and IMU with wheel encder and indicator box [4].
7) Indicator box
Indicator box is used to know condition of MMS hardaware components also to know signal of GPS and GLONASS [4].
1.2.2 Software Component
There are two softwares that used in MMS. There are Mobile Master Field (MMF) and Mobile Master Office (MMO).
1) Mobile Master Field (MMF)
MMF is used when collecting data with TOPCON IP-S3 HD1. It is important to put laptop with MMF installed in the vehicle. MMF can plan route of data collecting and also monitor all the hardware components sensor. In MMF, there is playback function to see the result of data that has been collected.
The result of MMF is position data, point cloud, and panoramic image [4].
2) Mobile Master Office (MMO)
MMO is used after collecting data with TOPCON IP-S3 HD1. In MMO, it is needed rinex data from base station. Rinex data is obtained from Continuously Operating Reference Stations (CORS) in the area of data collecting. MMO can integrate the measurement of IMU, GNSS receiver, and wheel encode. It also can show post processing data from base station, adjustment trajectory, generating cloud, panoramic images and trajectory.
The result of MMO is trajectory data, 3D point cloud data and panoramic image data [4].