How to calculate resolution at altitude

hey I’m trying to figure out if any one knows what hight you would need to be at when taking a photo from your phantom pro or inspire with 12mp 4000x2250 resolution to achieve one pixel per square foot. I’m trying to make a chart so i can then calculate distance between objects when taking standard photos not just making the area. any info would be greatly appreciated.

Hi Alex,

Are you wanting to have a map at a specific resolution (30cm per pixel), or are you wanting to measure distance between objects, and using the pixel approach as a means to do it?

I would like to measure objects using the pixel approach so lets say I fly at 100ft and my camera is 12mp with a resolution of 4000x2250 I’m trying to figure out how many pixels per square foot there would be and so on to 200ft 300ft ect. this would be useful to figure out the total area in the photo length x width

Thank you!

Hi Alex,

We have a measurement tool which lets you measure the length or a straight line, or a number of straight lines, as well as the area of any polygon you choose - would this solve your issue? Or are you focused on using the pixel based approach?

I’m trying to figure out the pixel based, as the area where I would like to take a photo from a specific height has buildings on either side so it cannot be sadly mapped. Would you know or have an question to figure this out ? Thank you !

It looks like you’re trying to calculate GSD? There’s a handly little Spreadsheet that Pix4d makes available -

I treat the p3 camera parameters like the 35mm full frame equivalents and it seems to be working well
36mm Sensor width, 20mm Focal length and 4000px image widthe are the parameters I use for the P3.

Thank you! that was what i was looking for

Hello Jono,

I am looking at a similar situation using the DJI Phantom 3 Professional and the Pix4D GSD Calculator. According to the Pix4D User Manual, you need to calculate the GSD from the following variables: Real Sensor Width (Sw), Real Focal Length (Fr), Flight Height (H), and Image Width (imW).

The real sensor width (Sw) should be provided from DJI’s specification for the imaging sensor used - Sony EXROM R BSI 1/2.3" Sensor. I contacted Sony and DJI and was not able to find the exact sensor datasheet at this time, although found a article online providing a reference to sensor sizes Click Here. According to this article, the sensor should have approximately the following dimensions: Real Sensor Width = 6.17mm and Real Sensor Height = 4.55mm.

Next, you need to calculate the Real Focal Length (Fr) provided DJI’s camera is a 20mm focal length (35mm equivalent). Therefore, users should calculate the Real Focal Length (Fr) from the equation specified in Pix4D’s user manual, Page 15.

The equation is as follows: Fr = (F35*Sw)/34.6

Too my understanding we should assign the value of 20mm for F35, therefore F35=20mm to calculate the Real Focal Length (Fr).

As a result Fr = (20 * 6.17) /34.6 = 3.57mm

After that is complete, you should be able to substitute the calculated value and documented values into the Pix4D GSD Calculator Spreadsheet:

  1. Fr = 3.57mm
  2. Sw = 6.17mm
  3. imW = 4000 pixels
  4. H = Any flying altitude given in the units of meters (m)

Are these calculations, numbers, and methodology correct?

I’m wondering this aswell. How can we calculate the resolution? For example if we want 30cm per pixel, at which height we need to fly?

im using DJI Phantom 3 pro and pix4d…, i want to take a photo for 15 hectares area… but im stuck with the mission grid from pix4d…help me

Why not use dronedeploy if you’re stuck with pix4d?

Hello guys. I would like to know about the information DD provide when planning a mission. DD provide information of definition (pixel size) but that definition is based on what kind of camera? How many Mp? Thanks in advance. Carlos.

If you’re planning on desktop it will assume an X3 or phantom 3 advance/pro camera. If you have another camera connected when going to fly, it will adjust your plan correctly. Now that more cameras are becoming available, there should be a way to select which camera you plan to use coming in the future.

Hola! un gusto saludarle esperando se encuentre bien!

Cuales son los parámetros de:

Focal Length =

Pixel Pitch (microns) =

X Resolution =

Y Resolution =

Gracias por su respuesta.


Alrighty, a lot of discussion, but I found that it’s just simple geometry. We have a P4P with a camera that shoots a 4864x3684 pixel image. The camera has a Field of View (FOV) of 94 degrees.

Just assuming that the FOV of 90, then you have a triangle with 45 degree angle (isosceles or whatever), which means that the height is same as the base leg. Therefore the width of the view at any heigth is 2 x Altitude.

So using basic math the resolution is;
Res (in/px) = 2 x Altitude x 12 in/ft / 4864 pixels

And finally for the P4P camera;
100 ft = 0.5 in/px
200 ft = 1.0 in’px
300 ft = 1.5 in/px
400 ft = 2.0 in/px
+400 ft = no bueno!

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Can you help and do this for the DJI Inspire 2 with the X5S with 15MM please…