Image acquisition plan for terrain with height variations

Single flight following the terrain elevation variation (recommended)

It is the recommended method since the GSD will be constant for the project since the height difference between the UAV and the terrain is maintained. 

 
Information: For more information about the GSD: Ground sampling distance (GSD).
Figure 1. Single flight following the terrain height variations.

Multiple flights at different constant altitudes

Perform multiple flights at different altitudes with the flight lines perpendicular to the slope. It is important that the there is overlap between the flights.

The GSD will be approximately constant for the project since the height difference between the UAV and the terrain is maintained.

 
Information: For more information about the GSD: Ground sampling distance (GSD).
Figure 2. Multiple flights at different altitude.

Single flight at a constant altitude regardless of the terrain changes in altitude (not recommended)

If the height difference between the UAV and the terrain is not maintained (keeping constant flight altitude):

  • It will affect the GSD: The GSD will not be the same over the whole project because of the variations in elevation of the terrain. In Figure 3, the obtained GSD in A has less resolution than in B.
  • It will affect the overlap: The overlap will be lower in the higher point B, if the image rate is the maintained.
  • It may affect the reconstruction or even fail if the height difference between the higher and lower point is twice or higher (if the highest GSD exceed twice the lowest GSD)
 
Information: For more information about the GSD: Ground sampling distance (GSD).
Figure 3. Constant flight altitude.

 

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7 comments

  • Jacob Beaton

    We have a farm with 100+m height variations. We would like to map "Single flight following the terrain elevation variation" (recommended) but I can't find the option in the pix4dmapper app - is it on by default? Is there another app I should use?

  • Momtanu (Pix4D)

    Pix4Dcapture does not have this feature yet but a lot of users have requested this feature. There is an app my colleague has used, it is called map pilot (it is not free and is available only for ios). However, they have this feature.

  • Scott Watson

    I'd be very interested in having this functionality as well, as we often fly projects in small canyons and gullies (sample below) that can vary by 200+ feet in elevation.  I've looked at the "Map Pilot" app that offers this option, but would prefer using your app.  Also, we're in an airport flight restricted area, so are limited to a max of 200 ft agl for most flights.

    Edited by Scott Watson
  • hamidreza rajabzade

    Hi How to set "Single flight following the terrain elevation variation" on pix4d capture app in android or ios or PC?
    please help me ...
    This option very very important for my work...
    Is this feature in the app? When will this update be available to users?

    My drone : phantom 4 pro v2

    Edited by hamidreza rajabzade
  • Gaël (Pix4D)

    Hi Hamidreza,

    The terrain awareness functionality has not been implemented either on Android or iOS version of Pix4Dcapture. In other words your drone will not follow the terrain elevation variations. At the moment, it is not in our pipeline to implement this functionality.

    If this functionality is very important for you, I would suggest looking at other third-party applications as some of them may include this functionality. Note that if they have it, you will probably have to pay for it.

    In any case, Pix4D's image processing engine supports images that are captured with any third party flight planning application as long as you have sufficient image overlap for your project.

    Best,

  • hamidreza rajabzade

    Thank you for your answer
    But the text of this post and title "Single flight following the terrain elevation variation (recommended)" made me question this
    Is this post and text not related to pix4d?

    Edited by hamidreza rajabzade
  • James Smith

    It is all well and good which way is the best way to accomplish getting similar GSD. The question is how do you figure out the angle of the terrain and how many flight lines you will need for a given length to be mapped?

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