# Backpack Acquisition - Best Practices

## Configure LiDAR Measurement Program and LPS

* Power on the system and connect to rover via Spatial Explorer 
* At the top of the screen navigate to Settings > Rover

![Configure Measurement Program (PRR) and Lines per second (LPS)](https://lh4.googleusercontent.com/h3CdnnneGs7TTRE_RUU0v8XqKEn5QPG8E4-0kUBxxjjdeJxqD8USHFPflTBWCrQyrhsYq-Rvd3drsVDW52d1uTs2XkiIFIbPXwvidV1MfY6Jio1U3LaPNZ-d3uFs_K9ewL8DUzD4)

* Ensure the Angular range of the sensor is configured to capture the maximum FOV
* 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 
* The table below shows recommended sensor configurations based on desired target range:

### Recommended Sensor Configurations for Backpack-based LiDAR Acquisition

|   System   | Target Range (m) |        Measurement Program (PRR)       | Lines Per Second (LPS)\* |
| :--------: | :--------------: | :------------------------------------: | :----------------------: |
|  Ranger-HA |         5        | VUX1-HA 1000 KHz (reduced laser power) |            200           |
|            |        20        | VUX1-HA 1000 KHz (reduced laser power) |            100           |
|            |        50        | VUX1-HA 1000 KHz (reduced laser power) |            65            |
|  Ranger-LR |         5        |  VUX1-LR 820 KHz (reduced laser power) |            185           |
|            |        20        |  VUX1-LR 820 KHz (reduced laser power) |            90            |
|            |        50        |  VUX1-LR 820 KHz (reduced laser power) |            60            |
| Ranger-UAV |         5        | VUX1-UAV 550 KHz (reduced laser power) |            150           |
|            |        20        | VUX1-UAV 550 KHz (reduced laser power) |            75            |
|            |        50        | VUX1-UAV 550 KHz (reduced laser power) |            50            |

{% hint style="info" %}
\*Recommended LPS computed based on the average walking speed of 1.3 meters/second for uniform point spacing at the desired target range
{% endhint %}

## INS Static Alignment Strategy (FOG IMUs # 32-60)

1. Collecting stationary data during the alignment is important for Fiber Obtic Gyro (FOG) IMUs as they are capable of static alignment.
2. 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.
3. Begin and end the backpack survey with the backpack sitting static in the upright position, with stabilizing poles extended, and in an area with reasonable open views of the sky for 3-5 minutes. 

 

![Static Alignment using Stabilizing Poles](/files/-MfdDt-A2y12EH88ksSV)

## INS Kinematic Alignment Strategy (All IMUs)

Per [Novatel’s Recommendations](https://docs.novatel.com/Waypoint/Content/AppNotes/BackpackSystems.htm), the following should be performed in the field for backpack acquisition:

1. IMPORTANT: Begin and end the backpack survey walking in an area with reasonably open views of the sky.
2. It is recommended that at least 30 to 40 seconds of data be collected while walking 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. 
3. 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.


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