Photogrammetry With UAS

Figure 1: Example of Photogrammetry in use

Introduction:

Mapping large swaths of land can be very helpful in a variety of applications, be it agriculture, land surveying, construction, or real estate. Making these models the traditional way is time consuming and expensive, and not always that accurate. Enter UAS, new approaches to many problems have come out with the rise in UAS in the last few years. This is even more true in terms of mapping. UAVs are lightweight, cheap and in terms of quad-copters can focus on an area for longer than a manned aircraft. By using this new tool, you can collect a variety of data and images, which can then be processed by a variety of software. One such way to process data is photogrammetry, or orthographic images. By using software such as Pix4d, you can piece together multiple images to form one cohesive whole, which can be utilized in a variety of ways.

What is Photogrammetry:

In laymen's terms photogrammetry sort of works by using images as pieces of a puzzle, albeit with multiple vantage points. Similar to how your eyes work, images taken for photogrammetric images have multiple view points to establish depth in the model, as well as perspective from the separate points of observation. 

Figure 2: Model of a shed

After the images are taken, the software in use needs a way to piece them together, this is accomplished by the use of tie points. Tie points function as a sort of anchor on each image, usually an easily definable point or object on an image that is also present in the next image in the pattern. After tie points are established they are overlaid on each other to being to form the model. 

Next ground control points are formed. These ground control points assign geospatial coordinates to images and then orients them into the bigger picture or model. 

Finally there is bundle adjustment. This allows the software to look for unnatural overlap or imperfections in the predicted image to then be fixed. This minimizes distortion in the model and helps form a cohesive image.

Uses:

The uses for Photogrammetry are vast, and more functionality to software's using this technique are being released as time goes on. Once data has been collected, there are many different final products that can be developed such as; Digital surface models, digital terrain models, contouring images, and many more depending on your need. Below are some examples of the different models.

Figure 3: Digital Surface Model 

Figure 4: Digital Terrain Model

Figure 5: Active Contouring Effect.

Pros and Cons:

As with most new technological developments, there are advantages and disadvantages. The main advantages to using UAS for this instead of manned aircraft are as follows:

• Cheaper than manned.
• More stable image collection.
• Mutiple vehicles can be used.
• Certain UAVs can hover over an area.

However, there are still times when using a manned aircraft is viable, mainly due to the disadvantages of UAS:

• UAVs cannot fly over 400 ft without a waiver, which takes a long time to receive.
• People are familiar with using manned aircraft.
• UAVs do not always have a long flight time and must land to change batteries.

Conclusion:

New data processing techniques are very useful, such as photogrammetry. Being able to piece together large models or images allows for swift and efficient application and dissemination of data. Besides efficiency, the number of options available to the operator makes a wide array of unique applications available. Because of all this, learning how to properly capture and develop photogrammetric images and models will help an operator acquire useful skills to help them in the market, improving their usefulness and hire-ability.