Lab Seven: Volumetrics with UAS Data

Introduction

In this week's lab, our class focussed on discovering the volumes of a specific area using the Wolfpaving data and the newly used Litchfield data set. The volumetric analysis consists of calculating various amounts of particular terrains to see changes throughout a period of time or determine the depth of what you are measuring. This can be accomplished by using a DSM (ArcGisPro) or a 3D model map (Pix4d). In this lab, we calculated the volume of a pair of stockpiles that were discovered at the Litchfield and Wolfpaving mining locations. UAS data is high when wanting to analyze various volumes of terrains. UAS data achieves different elevations to build a 3D model on an application. Using volumetric analysis, we are able to discover the amounts, making UAS data collected one of the best ways to find tools like these.  

Methods 

We first started out using the application, Pix4D, and the data set from Wolfpaving. We were tasked to calculate the volumes of a stockpile located in the northeast corner of our pictured data set. The following steps to do this are as follows:

Project--> Volumes--> (Outline the desired area using the mouse of your computer)--> Right Click--> "Calculate" 

There is also a setting to change the way the volume is calculated under volume settings. These consist of:

• Triangulated
• FLT Plane
• Align with average altitude 
• Align with Lowest Point
• Align with Highest Point
• Custom Alt. 

We used the calculations for all these settings to see the differences in outputs that were evaluated for the volumes. 

Figure 1 (Pix4D Calculating Volumes)

We then moved back to ArcGIS Pro to build maps and discover the progression of the stockpiles. We needed first to extract the section we wanted to focus on. This is accomplished by creating a new feature class in the database. Once established, we will be able to extract the area using a polygon tool and click around the area of interest. Once the area is outlined, you use the tool, " Extract by Mass," to create that new layer that is solely the stockpiles. Now that we can focus on a specific section (layer) calculating in that area has become a whole lot easier (Figure 2). The last step is to go back to the geoprocessing pane and find the "surface volume" pane to calculate. One of the is to know what the plane height is. To do this, all we need to do is click around the edges of our new highlighted layer to pull up that number. Once that is inputted, and we click "run," and surface volume calculations have been formed. A table will be developed in the contents, along the bottom.

Figure 2 (Extracting Stockpile & Calculating Volume)

Figure 3 (Map Created to show Volume Calculations and Exerted Hillshade)

Next, we moved onto the Litchfield data set location. This area was also a mine site and had data collected over a period of three months. (July 22nd, Aug. 27th & Sept. 30th, 2017). I took the data and moved into the ArcGisPro application. For this assignment, we needed to compare the pile over some time to see how much the terrain changed. Resampling the data was one of the first steps to accomplish. This makes sure that the information is correctly scaled and matches each of the layers we add-in. The "resample" tool allows us to carry out this step. It was noted that we resample the data to 10cm. Since we had an exerted pile and the layer of the whole site, we were able to compare the change of volume of the specific dates listed above. I also created a small map that showed the total change over the entire time. This final step was accomplished using the "cut fill" tool to show the net gain and loss of volume for the Litchfield data set (figure 4).

Figure 4 (Litchfield Elevation Progression Map)

Discussion

The data from Pix4d and ArcGIS Pro can be compared, looking a the table provided in figure 3 and the table created in (figure 5). Although ArcGIS Pro is the more accurate one to use, Pix4d is an excellent tool at providing an evaluation for volume. Compared to the Wolfpaving data set and the Litchfield data, Litchfield had more that we could work with. This was because there were multiple data sets taken on different days and could see the change over time. When taking data over some time, we must use the same Metadata. This includes using the same altitude, flight path, sensors, and the number of images taken. Any variations off this can result in alternated data that may not be accurate. If this isn't the step taken, resampling the data will also help and keep everything scaled the same. Also, GCPs need to be placed at the same base location; otherwise, the elevations will be off from data set to data set. Once all the processing and tasks were completed, I created the maps above to show a visual presentation of what I discovered. The map shows the highlighted extracted area as well as the whole site. I used multiple mini-maps to show the progression of the stockpiles. The other plan included the elevation and measurements from Pix4D compared to ArcGIS Pro. 

Figure 5 (Litchfield Data Set Min & Max Heights of Each DSM)

Conclusion

Volumetrics can be a beneficial tool, especially when it comes to UAS data. The comparison of something over time can be crucial for a lot of companies dealing with various terrains. Even though our main class focus is dealing with mine sites, this is just an example used to show how much more we can use it with.