Get the coordinates of a pixel from a georeferenced photo

[ricky1192]

Good morning,
I have a problem with geo-referenced photos from a DJI drone. I have the coordinates of the center of the photo and the metadata related to the photo and I would like to know how to go from a pixel to its relative coordinates.
Example metadata [Exif]:
latitude: 45.6426621388889
longitude: -94.5975223611111
AbsoluteAltitude: 332.743835
FlightPitchDegree: 0.3
FlightRollDegree: 3
FlightYawDegree: 89
GimbalPitchDegree: -90
GimbalRollDegree: 0
GimbalYawDegree: 7.8
RelativeAltitude: 40.700001
TlinearGain: 0
altitude: 332.7
altitude_ref: 0
aperture: 1.25
f_number: 1.25
focal_length: 13
image_make: "DJI"
image_model: "FLIR"

Having these and knowing that you have a box positioned at the pixels: 113 (xmin), 360 (ymin), 139 (xmax), 406 (ymax) how can I get its coordinates?

P.S. From a software I was able to extrapolate a solution that brings me back:
-94.6002156260815 (minimum longitude)
45.6413373184107 (minimum latitude)
-94.5998767997666 (maximum longitude)
45.6417408827611 (maximum latitude)
The problem is that I cannot understand whether it is right or whether it is calculated.
Thank you in advance

 

[Mossiback]

Math like that makes my head hurt, but I think you could verify by taking a picture of a site with known coordinates and then do the math to see if your formula/software is correct.

I am curious where the AbsoluteAltitude and RelativeAltitude figures come from.

 

[Meta4]

I have a problem with geo-referenced photos from a DJI drone. I have the coordinates of the center of the photo and the metadata related to the photo and I would like to know how to go from a pixel to its relative coordinates.

You really need to use multiple overlapping images to do photogrammetry rather than a single photo.
You could do something like this ...
An orthophoto of a 120 acre area, mapped by flying a precise grid and taking 400 images, exported into Google Earth will allow for what you want.

I am curious where the AbsoluteAltitude and RelativeAltitude figures come from.

They come from the Exif info which is included in every image the camera takes.
The absolute altitude is likely to be quite inaccurate and is not appropriate for calculations.

 

[Mossiback]

...They come from the Exif info which is included in every image the camera takes.
The absolute altitude is likely to be quite inaccurate and is not appropriate for calculations.

I know they come from the Exif info but I was wondering where the Exif info got it from since Go4 only shows height relative to the take off spot.

 

[Meta4]

I know they come from the Exif info but I was wondering where the Exif info got it from since Go4 only shows height relative to the take off spot.

Most software that displays Exif Info uses the term GPS Altitude, but the actual data all comes from the barometer.
The absolute altitude data is an interpolation based on standard air pressure and is usually quite inaccurate.

 

[Mossiback]

Most software that displays Exif Info uses the term GPS Altitude, but the actual data all comes from the barometer.
The absolute altitude data is an interpolation based on standard air pressure and is usually quite inaccurate.

Okay, thanks for the info. It's too bad Go 4 doesn't let us calibrate/correct the barometer.

 

[ricky1192]

You really need to use multiple overlapping images to do photogrammetry rather than a single photo.
You could do something like this ...
An orthophoto of a 120 acre area, mapped by flying a precise grid and taking 400 images, exported into Google Earth will allow for what you want.

They come from the Exif info which is included in every image the camera takes.
The absolute altitude is likely to be quite inaccurate and is not appropriate for calculations.

Thanks for the answer but my intent is not really that. I need to understand only the area that frames the photo, to make it "easy" the coordinates (latitude and longitude) of the four vertices of the image

 

[jamman]

I right clicked on a picture taken with my Mavic 3 and went to Details to show the GPS coordinates and it's showing a long series of numbers such as 38; 31; 7.11569999999482. How do I convert this to a simple 7 digit format? Any help is appreciated.

 

[PanoVolo]

GPS coordinates can be represented in DMS, DD, DDM formats. There are formulas to convert between the formats, look them up.

 

[MS Coast]

Is the location information in the EXIF information not the location of the camera rather than the location of the center of the image?

Unless the camera is pointed 90 degrees down, the lateral positions of the camera and the center of the photo subject will be quite different.

 

[PanoVolo]

it's a location of the drone when the picture was taken. There are also yaw-pitch-roll for the drone, and yaw-pitch-roll for the gimbal.

In theory you can calculate the location where the center of the frame is pointing to in the real world. In practice not so much because you need to know the precise altitude of the drone above the current ground level. And that information is not available with enough precision, I'm afraid.

 

[MS Coast]

it's a location of the drone when the picture was taken. There are also yaw-pitch-roll for the drone, and yaw-pitch-roll for the gimbal.

In theory you can calculate the location where the center of the frame is pointing to in the real world. In practice not so much because you need to know the precise altitude of the drone above the current ground level. And that information is not available with enough precision, I'm afraid.

It's trigonometry. You'd also need the elevation of the point in the photo you're evaluating, or the distance from the drone.