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Ground Offset

Tudor -

As of Map Pilot version 2.0.0 it is possible to areas that are higher or lower than the takeoff point to facilitate accurate overlap calculation for varying terrain.

 

This image shows that a ground offset of 20.3 meters has been selected with the standard 75/75 overlap setting. This will make it so that the 75/75 overlap will be calculated for a plane that is 20.3 meters higher than the takeoff point.

This is especially useful when you are trying to map a roof, treetop canopy, hill or valley where the it would have been difficult to get proper overlap without this setting.

It is possible to adjust the ground offset up to 50% of the selected flight altitude. 

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Comments

  • Avatar
    Ed Easterling

    "This will make it so that the 75/75 overlap will be calculated for a plane that is 20.3 meters higher than the takeoff point."

    I'm seeking to understand the effects of adjusting Offset. The comment from above implies that the mission configuration changes based upon the setting. Yet it does not appears to change the path, images, etc. in the way that Overlap changes them. What are the effects of (and reason to) changing Offset? I create aerials over 150' trees and am very interested in this function. Thanks in advance.

  • Avatar
    Zane

    The ground offset feature is designed to get the designated overlap on an area that is at a different elevation than the takeoff point. Imagine you want to get 70% overlap for the roof of a building that is 20 meters tall and you want to take off from the ground. Before you would have had to guess at how much higher you would need to put the overlap setting to get that value up there. Now you can use all of the normal controls for overlap and desired GSD/altitude and put in that ground offset to take care of the rest. Basically it just slides the exact flight plan that is shown up and down in altitude.

  • Avatar
    David Rodin

    Will setting a ground offset have any impact on the drone's altitude itself?

  • Avatar
    Bert Bosman

    I am very interested in an answer to the above question, while playing with offset i expected to see longer flight times/ more pictures ( or less depending on + offset or - offset).

    With an altitude set of 80 meters and offset to 20 meters will the quad fly at 100 meters ??

  • Avatar
    Zane

    All the Ground Offset feature does is move the flight plan up or down in altitude to let you optimize the overlap for a height other than the ground where you take off. All the images are taken at careful spacing to get appropriate overlap with reference to the takeoff location. If you are shooting the top of a building or tree canopy for example, you would use a +20 meter ground offset. Otherwise, your 70/70 setting is going to be more like 55/55 and not be very good.

    Bert: It will not affect the number of images taken or the spacing of the passes which is why you are seeing very little change in the flight stats. If you have a positive 20 meter offset and your flight altitude is set to 80 meters it will fly 80 meters above a point that is 20 meters off the ground, or 100 m.

    As of Map Pilot 2.1.6 this feature now works with the Terrain Awareness feature.

  • Avatar
    Veha La

    Hi Zane,

    "If you have a positive 20 meter offset and your flight altitude is set to 80 meters it will fly 80 meters above a point that is 20 meters off the ground, or 100 m." Does it mean it will fly at 100m for the whole project (without Terrain Awareness)?

    We want to map a mountain area with 150m at peak and want to get 10cm GSD with Phantom 4. Normally, to achieve this it will fly at 230m without Ground Offset, so if we set Ground Offset = 100m, it will fly at 330m for the whole project?

  • Avatar
    John Waite

    "It is possible to adjust the ground offset up to 50% of the selected flight altitude."

    What is point of this limit?

    If you need to have a ground offset of 70m (trees frequently grow to this height and taller in the tropics) but still want to map at high resolution (say 30 or 40m) why is this not allowed for? Best you allow is setting flight height at 67m and offset of 33m and then you are forced to mess about with overlap percentage.

  • Avatar
    Mike Morellato

    You mention in a comment above that this feature "now works with Terrain Awareness". If you're successfully using Terrain Awareness to keep the GSD consistent, are there situations where you would also use an offset? That's the confusing part to me. Would it be in situations where you are mapping mostly a built-up environment, as opposed to just varied topography that would already be picked up in SRTM data? Thanks

  • Avatar
    Zane

    Imagine mapping an area with 100ft tall trees everywhere. The overlap gets calculated assuming it is collecting images on the ground. The 100ft top of the tree canopy would get much less overlap than prescribed in the settings. The Ground Offset feature moves the plane for which the overlap gets calculated up to the level of interest, not necessarily the ground. The same is true for building roofs and things like that.

  • Avatar
    Mike Morellato

    Thanks for the extra details, that makes sense regarding the overlap numbers remaining accurate after using offset.

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