Mobile Acquisition
LiDAR Recommendations
Ensure the Angular range of the sensor is configured to capture the maximum FOV
For the Ranger series, It is recommended to select the reduced power measurement program in order to optimize the laser power for measurements of short range targets using the highest pulse repetition rate. This will reduce MTA ambiguities in short range mobile mapping applications
If available, set the Ranger or miniRanger to a measurement program with a reduced power mode to prevent laser damage from high-reflectivity nearby objects.
Be aware of LiDAR minimum range when planning drive path
Consider the possibility of laser shadow areas caused by terrain (freeway ramps) or features and plan multiple passes in different lanes/directions as needed.
Disable LiDAR sensor at long stops to minimize duplicate points
Imagery Recommendations
Configure the ladybug camera to be triggered by SpatialExplorer, refer to the ladybug setup manual. Trigger the Ladybug camera by distance to ensure quality image overlap and to reduce the number of duplicate images at stops.
If you do not have a ladybug camera, it is not recommended to activate/trigger your camera at all during the drive
Do not rely on quality imagery for distant objects (more than 20-30m) for asset inventory
Mission Tips
Drive at night to avoid sitting at stop lights and to minimize car-shadows in data (unless you are also co-acquiring imagery)
Consider splitting total drive path into several smaller trajectories (plan accordingly with heading maneuvers)
PLS Recommends keeping your AOI to within 10 kilometers of the GNSS Base station. If you have a very large area that needs to be mapped along a corridor, breaking the job up into 10-20 km sections that overlap is better for processing and acquisition. Place the GNSS Base station in the middle of each section and run the base throughout the entire collection process for that section. See a visual example below.
Consider using a wheel sensor to mitigate IMU drift and poor positioning accuracy during long periods without movement and in areas with poor satellite coverage
Drive quickly through tunnels and under bridges to minimize time without GNSS coverage
Ensure base station is set up as close as possible to collection area, especially areas that are expected to have poor GNSS coverage. PLS recommends keeping the GNSS base within 10km of the total AOI.
Set out ground control targets at regular intervals, and collect accurate ground control coordinates at the center of each target to be utilized as ground truth in trajectory/cloud optimization routines
Perform several figure 8’s along the drive path to improve GNSS/IMU coupling (Ideally in open areas with good GNSS coverage)
INS Kinematic Alignment Strategy (All IMUs)
IMPORTANT: Begin and end the mobile survey driving in an area with reasonably open views of the sky.
Perform a strong heading alignment by driving fast and straight at the beginning and end of scanning. We recommend a heading alignment of approximately 10 seconds of data be collected while driving at a constant heading (before and after survey). This will ensure that an initial position, velocity and heading can be determined from the GNSS data, which is required by the alignment process. (do it in a safe place!)
Following this initial coarse alignment procedure, several changes in heading (left and right turns) should be performed to maximize attitude convergence prior to entering challenging GNSS conditions. Our recommendation is a figure-8 pattern if possible.
INS Static Alignment Strategy (FOG IMUs #32-60)
IMPORTANT: When using a FOG IMU, ensure the vehicle is not running and LiDAR is not spinning during static alignment.
Collecting stationary data during the alignment is important for Fiber Optic Gyro (FOG) IMUs as they are capable of static alignment.
Static alignment uses the sensed gravity vector components to estimate roll and pitch. It uses sensed Earth-rotation rate to provide an initial estimate of the yaw of the IMU. As such, only IMUs with gyro biases much less than the Earth rate (15 deg/hr at the equator) are capable of reliable static alignment.
Begin and end the mobile survey in an area with reasonable open views of the sky for 3-5 minutes.
Operating the Ladybug Camera
For the Ladybug, it must be plugged into the notebook through a USB3 port, any other port less than USB3 will provide unreliable operation. From the LadyBugCapPro app, configure the ladybug settings as highlighted in the figures below. Set Data format to JPEG (12bit) GIS, and Shutter ranger range to Drive Highway. On the GPS tab, check Start GPS Time Sync. Finally under camera settings under trigger strobe, to Enable trigger and set GPIO1 to Low polarity and 10.00ms duration. For more information regarding the details for operating the Ladybug camera, go here .
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