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Author Topic: Altitude or height.  (Read 1358 times)

pmgzamorano

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Altitude or height.
« on: February 20, 2016, 12:12:27 PM »
Good Morning.
I uploaded some photos taken with a phantom and altitude drone presented is the height of the camera above the ground. Control points are taken with GPS and their altitudes are relative to mean sea level How do I resolve these differences ?.

Thanks for everything and best regards.

HMArnold

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Re: Altitude or height.
« Reply #1 on: February 20, 2016, 10:34:25 PM »
The answer is not good

If you look closely at the altitude values in the EXIF you will find that the values are off by sometimes hundreds of feet because they are derived from the GPS Altitude, which is much less accurate than lat and lon.

I live very near the coast and my EXIF altitudes usually come out below sea level

Another problem is that for both my P3P units, the EXIF altitude values come out in feet, but WGS84 takes them in as meters.

To my knowledge there is no way to correct these values on the platform,  or to switch the EXIF to record height above ground, which has enough accuracy to almost be able to land softly with.

There had been some posts about height above ground being in the EXIF info as a non-standard tag, but I looked at the individual tags and could not find an accurate value

The best solution I know of is to download the flight log and create an Agisoft import file based upon those values, which not only gives you height above ground but also the gimbal angle (pitch) and camera direction  (yaw)

Inclusion of these values also significantly helps Photoscan in the alignment process

Anxious to hear other solutions

dsheehan

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Re: Altitude or height.
« Reply #2 on: December 07, 2017, 12:01:15 AM »
Looking at the Omega Phi Kappa, which is pitch and which is yaw? 

First three lines of the OPK file output from Photoscan:

# Cameras (32)
# PhotoID, X, Y, Z, Omega, Phi, Kappa, r11, r12, r13, r21, r22, r23, r31, r32, r33
DJI_0464.JPG   334431.9611538954800000   7216944.2492030482000000   217.4452483703651100   85.6828479713175570   -82.617933788249616   -3.8434413251724098


Alexey Pasumansky

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Re: Altitude or height.
« Reply #3 on: December 07, 2017, 12:06:10 AM »
Hello dsheehan,

There are no yaw, pitch or roll angles in Omega, Phi, Kappa format export.
Best regards,
Alexey Pasumansky,
AgiSoft LLC

SAV

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Re: Altitude or height.
« Reply #4 on: December 07, 2017, 06:18:56 AM »
Hi pmgzamorano,

Several solutions:

1. Fix the Z value in EXIF by adding the altitude relative to mean sea level of the point of take-off to your flight height above point of take-off (which is recorded by your DJI drone). Can be done using a custom Python script.

2. Adjust the accuracy settings for ground control points and camera locations. If you enter a very large number for camera accuracy (Photoscan default value is 10m) and a low number for marker accuracy (default is 0.005m), then the optimisation and height of the model will mainly depend on the Z value of your your ground control points/markers.

3. Uncheck all images in the reference pane so Photoscan will ignore their locations during Photo alignment.

Regards,
SAV



Good Morning.
I uploaded some photos taken with a phantom and altitude drone presented is the height of the camera above the ground. Control points are taken with GPS and their altitudes are relative to mean sea level How do I resolve these differences ?.

Thanks for everything and best regards.
« Last Edit: December 07, 2017, 06:20:43 AM by SAV »

dsheehan

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Re: Altitude or height.
« Reply #5 on: December 07, 2017, 05:51:20 PM »
Hello dsheehan,

There are no yaw, pitch or roll angles in Omega, Phi, Kappa format export.

Can you tell me how to convert Omega, Phi, Kappa, to direction the camera is facing and angle from the horizontal?