Direct georeferencing (or geopositioning) is a technology that captures the GPS location and IMU orientation of individual images. This is beneficial because knowing the GPS and IMU data for each individual image greatly improves SfM processing time. Also, if the GCP and IMU information is accurate enough, it can be used to accurately scale the SfM-produced information.

Anything in your data set can be considered a scale bar if you know it’s true measurements by physically measuring the scale bar. That measurement is then used in software to scale the model. Typically, a scale bar is an elongated rectangle that is no longer than a meter. Scale bars can be as simple as a meter stick or as complex as a custom printed photogrammetry target panel.

Many sUAS and some sensors have an integrated GPS that “tags” the image or sensed information with a GPS location. This is commonly referred to as a geotag. These geotags are helpful because they give a rough location (typical trusted accuracy of 1-3 meters in XY and 3-5 meters in Z) of where the data was captured. This greatly improves processing time for structure from motion workflows. Though technically a form of direct georeferencing, these type of geotags are not referred to in that context because of their low accuracy.

Multirotor aircraft are inherently easier to fly because they do not require forward movement to stay aloft. These are the best systems for beginners. Fixed-wing aircraft are more difficult to operate because the must always travel forward to stay aloft. However, advancements in programming have simplified their operation. Single rotor aircraft can also be difficult, but their operation is improved with good programming as well.

Pay particular attention to the sUAS environmental limitations such as wind tolerance, operating temperature, and water proofing/resistance. These factors will impact your sUAS selection based on where you plan to operate it.

The size of your area of interest will impact which sUAS you select. Multirotor sUAS are well-suited for small areas (10s of acres) due to their limited endurance (typically 30 minutes or less). Fixed-wing sUAS are better suited for large areas (100s of acres).

One of the most important factors in sUAS selection is its capability to carry the indented payload(s). The sensor’s size, weight, and power (SWAP) requirements will determine which sUAS can feasibly carry the sensor for your mission.

Manned aircraft may be a better selection for your project if you need to cover large areas (1,000s of acres).

Here are some examples:

https://www.terravion.com/

https://www.eagleview.com/product/pictometry-imagery/

https://go.nearmap.com/

Satellite-sourced data may be ideal for your use if you need to cover very large areas (10,000s of acres). However, the greatest limiting factors to satellites are the spatial resolution of the data they produce and cloud interference.

Here are some examples:

https://landsat.usgs.gov/

https://www.digitalglobe.com/about/our-constellation

Large UAS are often limited to government and military use due to regulatory constraints. As regulatory conditions improve, their use will increase in the coming decades.

Here are some examples:

http://www.ga-asi.com/predator-c-avenger

https://www.nasa.gov/centers/armstrong/aircraft/GlobalHawk/index.html