### Resolution (GSD) for photogrammetry (3D mapping + DSM)

Hi everybody,

I am starting to plan the construction of a small plane to do photogrammetry, in special to do 3D mapping and the DSM.

I'm stuck in two questions:

• What is the resolution that you need to do, for example, a topographic map?

I saw some application and people used most of the time 1 to 5 cm of GSD, but is there any technical explanation or rule of thumb for this?

• Is it necessary to have an oblique camera to do 3D mapping or it is enough to have just the one facing downward?

If is necessary, what usually is done? You put two cameras or do the survey two times changing the position with a gimbal?

Thank you a lot!

#### Replies

• Hi Lui,

In response to your 1st question, please, note that since historically topographical maps were printed on paper the "resolution" (density or level of details) was identify based on their scale.

Links to good articles and tools on this matter are below

Relation between printing scale and GSD

Ground Sampling Distance (GSD)

TOOLS - GSD Calculator

Focal length and flight altitude vs Ground Sampling Distance

(you may or may not need to sign-up)

As for the 2nd question, camera only in NADIR position (facing downward) is enough for 3D mapping (DSM, DTM, Orthophoto Map). However, if you need to do a 3D scan of a building or structure or a tower, then you must use an oblique camera and take photos flying around a structure in circles of incremental heights.

More on this below:

Vertical / Oblique imagery

Image Acquisition Plan

Regards,

Vusal

Relation between the printing scale and the GSD
When the final output has to be printed, the printing scale has to be defined. Typical output to be printed is the orthomosaic as it serves as a map.…
• Hi Vusal,

Thank you for the information, it helped a lot!

Best regards,

Lui

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