Data Collection

From Ecosynth Wiki
Revision as of 11:47, 31 July 2014 by J Dandois (Talk | contribs)

(diff) ← Older revision | Latest revision (diff) | Newer revision → (diff)
Jump to: navigation, search

The Ecosynth data processing pipeline covers the steps necessary for preparing for a data collection mission, processing images into a 3D point cloud, then post-processing the point cloud data into useful data products like canopy height models (CHMs), digital terrain models (DTMs), maps of forest biomass density, and more. This is the most current version of the pipeline; for previous versions including retired platforms and procedures visit the Data Processing Archive.

Contents

Flight Planning

There are a number of perimeters that need to be taken into account while creating a flight path.

  • Generally flight paths represent a tradeoff between altitude, area, and time.
  • Tests have shown the following approximate maximum safe flight times carrying the appropriate number of 5000 mAh 14.8V lipo batteries, Astro dog tracker, and Canon SD4000 camera.
    • 10 minutes (approx. 3.0km) with a UDrones A-RTF Arducopter Hexacaopter carrying one battery
    • 12 minutes (approx. 4.0km) with a Hybrid Mikrokopter-Arducopter Hexacopter carrying one battery
    • 30 minutes (approx. 8.0km) with a Hybrid Mikrokopter-Arducopter Octocopter carrying four batteries
    • 17 minutes (approx. 5.0km) with a 3D Robotis X8 carrying one MaxAmps 11000mAh battery.
  • Missions can be planned out entirely from within Mission Planner, including accounting for desired photographic overlap for a particular camera model. Get Mission Planner here.
    • Ecosynth recommends very high photographic side overlap, at least > 50 %. Our standard is 75 % side overlap and > 90% forward overlap.
  • It is necessary to have basic information about the changes in terrain at the site, the height of trees and other features.
    • Flying height based on the parameters table should be estimated from the 'highest' object in the flight path.
    • Consider the height of where the copter will be launched from in relationship to the tallest features.
  • For example: A typical Ecosynth scan using a hybrid copter covers an 250m x 250m area of interest (AOI) flown 80m above the 40m high forest canopy with 25m track widths.


There are two main methods for creating a flight plan; directly in APM Mission Planner or in a GIS (we use ArcGIS) which is then uploaded to Mission Planner. This document will only cover the instructions for using Mission Planner, the reader is referred to the archives Data Processing Archive v2 for GIS instructions.


Design Flight Plan in Mission Planner

  1. Open Mission Planner and select “Flight Plan” in top menu bar.
  2. Locate your AOI by one of the following methods
    1. Right-click APM screen, select “Map Tool”, select “Zoom to”, type AOI location, and zoom as needed.
    2. Using Google Earth find the latitude and longitude coordinates for the center of your (AOI) and enter them in the home location.
    Right-click APM screen, select “Draw Polygon”, select “Add Polygon Point”. Add 4 points around your AOI. The location of these points can be altered by dragging them.
  3. Generate Waypoints by one of the following methods
    Method 1: SimpleGrid:
    Right-Click APM screen, select “Auto WP”, select “SimpleGrid”. A series of pop-up windows requiring values will appear.
    1. Relative Altitude- Height above launch point (canopy height + camera_model height)
    2. Distance between lines- Tract width
    3. Put a WP every x distance- Helps keep copter on straight flight path or to loiter along path. We find the copter does not deviate from path and enter -1 for our flights.
    4. Enter the line direction- The copter The AOI is often not oriented to north as in our example. To find the azimuth Left-click on a Polygon Point (note that nothing will appear on screen yet), right-click APM screen, select “Map Tool”, select “Measure Distance” (a point will be added), left-click on Polygon Point adjacent to first Point (again no point will appear), right-click APM screen, select “Map Tool”, select “Measure Distance”. The “AZ” value is the “Line Direction”
    Method 2: Survey(Grid):
    Right-Click APM screen, select “Auto WP”, select “Survey(Grid)”. A window will appear for generating waypoints.
    1. Coming soon.
  4. Change APM default values
    1. WP Radius- This is the minimum distance in meters the copter needs to be from the waypoint to be considered to have reached it before it continues to the next waypoint. This value is much too high for our purposes and should be changed to 5.
    2. Default Alt- This is the default height above launch point the copter will maintain in RTL (return to launch mode if RTL @ def Alt is checked. This height should be the same as your highest waypoint height.
    3. RTL @ def- If unchecked the copter will maintain the altitude it was at when switched to RTL. This this left checked so the default altitude is maintained.
    4. Verify Height- If checked Mission Planner will utilize Google Earth topography to adjust the copter altitude to the set altitude above the ground height beneath. For example, if you fly over gullies or hills the copter decrease or increase the altitude accordingly to maintain the set altitude above the ground. If left unchecked the copter will be kept at a constant height above the launch point altitude. This box should be checked.

Data Collection

Before leaving the lab go over the Flight Checklist to insure all field equipment is packed. In order to georeference the points the launch location elevation needs to be collected either in the field using a high-precision GPS unit, such as Trimble, or by extracting the value from a quality DEM in GIS. If using the GPS method it is recommended to start collecting positions point as soon at the launch location is reached.

Prepare Aircraft and Camera

Launch prep

  1. Turn on dog tracker on copter and the hand-held GPS unit
  2. Start up laptop
  3. Launch APM Tool Application
  4. Load the waypoint file
  5. Check that the flight distance is within safety boundaries
  6. Ensure WP Radius, Loiter Radius, and Default Alt have correct values. These tend to revert to default values.
  7. Check voltage on flight lipo battery
  8. Attach lipo to copter with velcro straps
  9. Plug lipo into copter
  10. Plug in laptop 3DR
  11. Check that the laptop and copter 3DRs are communicating
  12. Write waypoint file to copter
  13. Secure dome with zip-tie
  14. Place camera calibration target (Lastolite EZYBalance) in full sun
  15. Set up camera for Continuous Shooting (CS) mode using the simple method (a velcro strap) or the advanced method (CHDK):
    • In order to use the Canon PowerShot ELPH 520 hs for image collection it is necessary to keep the camera in Continuous Shooting (CS) mode throughout the duration of the flight. Conveniently, the camera will keep whatever exposure settings are applied at the first image, maintaining constant exposure throughout the flight. We have two main methods for 'keeping the shutter button pressed' during flight:
    Simple Method
    1. Turn on camera in manual shooting mode
    2. Adjust the function settings by clicking the "FUNC./SET" button
      • Set Light Metering to Spot
      • My Colors off
      • Daylight Auto White Balance is usually suitable
      • ISO between 200 or ISO 400 is usually suitable
      • Program in Rec. Mode
      • Self-Timer off
      • Continuous Drive Mode
      • 4:3 Still image aspect ratio
      • 10M recording pixels
      • Fine Compression
      • Default movie quality
    3. In the menu > Picture Settings:
      • AF Frame: Center
      • AF Frame Size: Normal
      • Digital Zoom: Standard
      • AF-Point Zoom: Off
      • Servo AF: Off
      • Continuous AF: Off
      • AF-Assist Beam: Off
      • Flash off
      • i-contrast: Off
      • Wind Filter: Off
      • Review: Off
      • Grid Lines: Off
      • IS Setting: Continuous,On
      • Date Stamp: Off
      • Face ID Settings: Off
    4. Set the camera to infinity focus (tap the tulip flower, then select infinity)
    5. Lightly tape a small piece of plastic, like a small extra plastic nut from the copter, to the shutter button (make sure not to depress the button
    6. Lightly wrap a velcro strap around the camera body
    7. Point camera at target with ISO 200 or 400 and shutter speed at least as fast as 1/800. Adjust shutter speed & ISO for good exposure on the target. Faster shutter speed is best.
    8. This part takes a little art: You need to use the velcro strap to push down the button while the camera is pointed at the calibration card, securing the velcro strap so that the button stays pressed. Make sure it is snug and can't wiggle off!
    9. Once you have the velcro strap secured, attach the camera to the copter and move on the next step.
    CHDK Method
    • The 'Simple' velcro method described above is very simple, but can be challenging for some people to get right. We also suggest using CHDK (Canon Hackers Development Kit) to enabling scripting of the continuous shooting mode. This does not require using the velcro strap to keep the button pressed.
    1. With CHDK and the continuous shooting script installed on the SD card
      1. Set SD card to lock position
      2. Insert SD card in camera
      3. Start camera in picture preview mode
      4. Navigate in the menu to Firmware Update and active the firmware update -- this initializes the CHDK firmware
    2. Load the fast intervalometer / continuous shooting script in CHDK and check that it is set to never stop taking pictures. You know this is set when additional information is displayed on the screen. This is tricky, so practice it.
    3. Assuming other settings are set as above
    4. Set the camera to infinity focus (tap the tulip flower, then select infinity)
    5. Point camera at target with ISO 200 or 400 and shutter speed at least as fast as 1/800. Adjust shutter speed & ISO for good exposure on the target. Faster shutter speed is best.
    6. Initiate the CHDK continuous shooting mode as per the onscreen instructions
    7. Attach camera to bottom of copter using velcro straps
  16. Time to Fly!

Fly the Mission

The following instructions are for autonomous launch, flight & landing. Instructions for manual launch and landing are in the Data Processing Archive.

Launch

These instructions are for APM 2.6 and may not be appropriate for a Pixhawk configuration.

  1. Move copter to open launch area
  2. Point red arm (forward) away from you
  3. Turn on transmitter and activate copter moving Throttle switch down and to right and hold there for 3 seconds (A on image below)
  4. Initiate automatic take-off or take-off manually to desired altitude
    1. To initiate auto take-off, apply a small amount of throttle to get the props spinning and then simultaneously switch the GPS and Height switches to their full on positions
      1. GPS 'GO' is position 0 on Flaps/Gyro for the Spektrum DX7 config we use (B in image)
      2. Height lock to position 0 on Gear/Mix switch (C in image)
    2. To do a manual take-off, apply throttle to launch copter to desired altitude
    3. When at desired altitude, initiate the auto mode by simultaneously switching on the GPS and Height switches as indicated above
  5. Once launched in auto mode, move the Throttle switch to the middle position
  6. Watch the unit fly its path. If line of sight is lost rely on the APM tool and the GPS hand-held unit for copter location

Ecosynth spektrum dx7 controls.jpg

Landing

  1. The copter will return to the launch location and land autonomously if the above flight plan directions were followed
  2. Allow the copter to descend to a few inches above the ground, then lower the Throttle complete and move the Height and GPS switches to the off position
  3. Deactivate copter by moving Throttle switch down and to left and hold there for 3 seconds
  4. Congratulations!

Post-Flight

Field
  1. Turn off transmitter
  2. Turn off camera
  3. Unplug lipo
  4. Turn off dog tracker & hand-held GPS unit if this is the last flight
  5. Verify that the flight photos are complete and uncorrupted
  6. Transfer photos to the laptop
  7. Pack equipment and head home
Lab
  1. Download telemetry files (.kmz, .txt & .gpx) from copter to processing computer
  2. Transfer photos to processing computer
  3. Recharge equipment- transmitter, lipo batteries, camera batteries, Garmin dog tracker & GPS hand-help unit
  4. Restock field kits if necessary
  5. Post-process launch location GPS data. This video gives directions for differential correction if using Trimble & Pathfinder Office.