Slight GSD variation when processing multiple flights of same area with same settings

Hi all,

We have a field of about 2 acres where we have sown wheat. I am flying Matrice Pro 600 with Altum sensor. I planned mission using Micasense Flight Calculator and set the optimal parameters. I am using DJI pilot to fly the mission. The pilot app shows that my GSD is 1.73cm/px.

Now, when I process both flights using same settings, I get different GSDs after initial processing without GCPs (1.7479 and 1.7697). After final processing without GCPs I get pixel resolution in QGIS around 0.01748000000000000248 and 0.01769000000000000088. So we added GCPs in field to check this variation but now my GSD is smaller but still different on both images.

I really need help if someone can. Is this normal? Our drone is not equipped with RTK, could this be the issue? Also, we don’t have an accurate GNSS to take exact coordinates of GCPs so what I did was to do processing of 1st flight and used MTP and exported them as GCPs for second flight. Read it somewhere that it should aligned my images, which it does but still GSD variation is that I can’t understand.

Hi @vakasahmad,

welcome to the Pix4D Community :handshake:

It’s normal to see slight variations in Ground Sampling Distance GSD between different flights, even when the same settings are used. This can be due to several factors, including slight variations in flight altitude, camera angle, and atmospheric conditions.

In your case, the differences in GSD that you’re observing 1.7479 and 1.7697 are relatively small and may not significantly impact the overall quality or accuracy of your results. However, it’s important to note that GSD can affect the level of detail in your images, and larger differences may be more noticeable.

As for your question about RTK, while it can help improve the accuracy of your geolocation data, it’s not directly related to the GSD. The GSD is primarily determined by your flight altitude and camera specifications.

Using Manual Tie Points MTPs as Ground Control Points GCPs for the second flight is a clever workaround when you don’t have an accurate GNSS. However, keep in mind that the accuracy of these GCPs is dependent on the accuracy of the first flight’s processing, so any errors or inaccuracies could be propagated to the second flight.

For more information on how GSD is calculated and how it influences your results, you may find these articles helpful:


Please note that these links are for illustrative purposes and are not actual screenshots or images. For actual screenshots, please refer to the original articles on the Pix4D support page.

I hope this information helps! If you have further questions, don’t hesitate to ask.