Volumetrics

 Volumetrics

Volumetrics by definition is the measurement of an object in terms of volume. Volumetrics can be immensely useful in many different scenarios. For this lab, it is a dredging operation and we are tasked with calculating the volume of different piles over the course of weeks. With UAS data and GIS, this can be done safely and efficiently. We were tasked with using ArcPro to calculate the volume of these piles using a DSM. These tools will be described in detail below.

• Extract by mask - allows the user to use a created feature class with a specified shape and create a raster clip of the desired DSM with said shape.
• Resample - allows the user to change the raster pixel size or the resampling type.
• Surface volume - takes a raster and calculates the total volume of it
• Cut fill - gives the user a visual representation of the elevation changes over two different rasters. 

 In order to calculate the volume of the piles, we first must be able to utilize the above features. The process essentially takes the DSM and creates a small clip or raster of a specific area. From here, the raster can then be used in tandem with the Surface Volume tool to calculate the volume. This is described in the steps below.

1. Insert the data set into ArcPro
2. Create a feature class under the database
3. Under the edit tab, create the shape of the polygon 
4. Use the extract by mask tool on the feature class and the DSM
5. The new mask is now created
6. Use the surface volume tool to calculate the volume
7. Cut fill to cut out a specific station if needed.

Before moving on to the data, there is something to note. These tools can take a very long time to process which is a large factor in completing a job on time. In my experience, processing data on Pix4D has taken anywhere from 30 minutes to 4 hours for small data sets. If you had a data set with thousands of images it could quite possibly take days. With this in mind, understanding the limits of your hardware and how long it will take to process data is essential in ensuring an operation is completed. For this lab, I remoted into a computer in our UAS lab which reduced the load on my own personal computer. The computers here are high end and the CPU was still running at maximum load. This is important to remember.

 This process can help to cut out a section of a DSM and calculate the volume of the area. Examples of this are shown below. Figure 1 shows a pile that was cut out and had the volume calculated. In the top right of the map, you can see the volume value as well as the 2D & 3D area.

(Figure.1 Wolfcreek Pile Volume)

The next few maps are from the same location, Litchfield. The same pile was calculated over the course of roughly 3 months in order to identify the volume of the pile throughout the dredging operation. This is a good example of a possible operation that we might be tasked to do.

(Figure.2 Litchfield 07/22/2017)

(Figure.3 Litchfield 08/27/2017)

(Figure.4 Litchfield 09/30/2017)

The following table also helps to reiterate the differences in volume between the 3 dates. This is a good component to have especially in a professional environment. Having multiple ways to deliver the data is essential to appeal to everyone's learning strategies.

Name:	10cm Volume	100cm Volume
Dsm_clip_x5_20170722	76317.5687	69238.4037
Dsm_clip_x5_20170827	165442.6917	188343.7291
Dsm_clip_x5_20170930	114943.3788	92713.6886

(Figure.5 Volume Table)

The last map shows the cut fill tool and how it can be used to show net gain and net loss. This tool was used on all 3 dates to show the differences over time of the volumes. This is another important visual to add to the documentation to show to the client. 

(Figure.6 Cut Fill)

The red areas on the map show the net gain. This is the area where the volume of the pile has increased over the course of the 3 months. The blue areas show the net loss which are the areas where the volume of the pile has decreased. One thing to note is the lack of actual values for the net gain and loss. This is a qualitative map and would work best when paired with an actual report or graph that shows the values of elevation change. 

Reflection

Volumetrics is a powerful concept to understand. For operations such as this, calculating the volume of the different piles can take days or even weeks. On top of that, in certain operations, it can be immensely dangerous for the crew involved. For this data set, the aircraft was flown for one day every three months and collected images. The data can then be processed within a few days with little to no error. However, this method is not without its flaws. Environmental obstacles can prove to cause issues with the quality and accuracy of the data.