Maps Made Easy Drones Made Easy

Ground Reference Images

Tudor -

Since DJI aircraft populate the image geotags with using the barometric altimeter (relative to the home point) and not the GPS altitude (absolute above sea level), Map Pilot automatically records an image at the takeoff point after the start of every mapping flight.

Include this image in your upload to Maps Made Easy for proper elevation offset calculation and elevation readings.

NOTE: Due to how Maps Made Easy uses ground reference images to correct for the use of the barometric altimeter in its elevation processing, it is highly recommended to take off from an area of undisturbed ground. Taking off from man-made structures or in areas of heavily modified earth will not correspond well to the reference values we get from the NASA SRTM elevation data and will result in elevation offsets.

 

Important for Multiple Takeoff Locations: If you are taking off from multiple takeoff locations, DO NOT upload the ground reference images with your data. We only use one ground reference image for the altitude corrections and if your reference images were taken from multiple elevations there is no way to control which on gets used. Uploading ground reference images from multiple elevations will likely do more harm than good. 

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Comments

  • Avatar
    flitelab

    Do you include this image in the selection with all the main images or separately when it prompts on the EXIF file request? Wasn't clear when and where I should include the file from the ground, included it as part of the full set.

  • Avatar
    Tudor

    The ground reference image (image taken when the aircraft lands) should be uploaded along with all of the other images.

  • Avatar
    Jos Bol
    Instead of taking the reference image when landing, could it (also) be taken at take off? We don't let our phantom land on the ground, but on our hands above our head. We end up with a cool picture of us looking up at the drone, but I doubt it's of any use :) .
  • Avatar
    TwoRivers

    Tudor - Can you please explain how not including these ground reference images will affaect the end product? What exactly will be adversely affected? I have created several maps where I exlcuded these images thinking they may be detrimental, not useful.

  • Avatar
    Zane
  • Avatar
    Doug Thost

    I recently flew a survey south of 60*S (in Antarctica) using Map Pilot, and processed on MME. The DEM is pretty close to what I expected to get, but I'm just wondering where the reference image sourced an elevation AMSL for calculations from. The shuttle data doesn't extend that far south. Did it just "get lucky" or is there another data set it can access? Airbus WorldDEM (he asked, hopefully)?

  • Avatar
    Tudor

    Sorry for the delay.
    It is embarrassing but we actually use the MapQuest elevation API for the ground reference image offset.

    https://developer.mapquest.com/documentation/open/elevation-api/elevation-profile/get/

    It has good coverage and good terms. We have no idea where they get their data for down there though.

  • Avatar
    Old Scout

    @Tudor @Jos Bol
    re: "The ground reference image (image taken when the aircraft lands) should be uploaded along with all of the other images."
    I, along with @Jos Bol, much prefer to "hand-catch" my drone slightly above my head at the end of a mission, especially on windy days. Is it required that I literally let the aircraft land on the ground before dis-engaging from the app, or can I dis-engage from the Map Pilot app after the last mapping image is taken, bring it home, hand-catch the drone, stop the rotors (with the battery still on and controller connected), place the drone on the ground at the takeoff point (under my feet) and simply manually snap an image and include it with my upload?? Sorry if this has already been addressed but can't seem to find a concise answer to this.

    Also..... what are the effects if I begin the mission if the drone is already at altitude?? (Example 200ft AGL)

    Edited by Old Scout
  • Avatar
    Zane

    The Ground Reference image is now taken when the aircraft takes off on most models (all but M600).

  • Avatar
    Old Scout

    @Zane... Understood. However, I don't take off from ground level. I launch with the drone held over my head. If I manually snap an image while the drone is sitting on the ground before the mission starts (before take off), will that image suffice and meet the definition of a "Ground Reference Image" as it pertains to MME processing?? Thanks in advance...

  • Avatar
    Zane

    OK. I thought you were saying that you caught it... I don't know when it is going to take that image then. Probably when the motors are shut off. Regardless, as long as you have an image that is taken at that location that is marked as the 0 altitude point it will work as a Ground Reference image. It may be off by a bit but it will be much better than using the GPS derived numbers.

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