Building Maps with Pix4D

Introduction

Why are proper cartographic skills essential in working with UAS data?

          Proper cartographic skills are essential in working with UAS for a number of reasons. Many people believe that just taking an aerial photo can be classified as map making but that is not the case. As discussed in further detail below, there are a number of things needed to make a make from data collected from a UAS. It is one thing to be able to collect data using a UAS and another to be able to get that UAS data into a form that it can be worked with in GIS and turn it into a map.

What are the fundamentals of turning either a drawing or an aerial image into a map?

         As discussed in the response above, an aerial photograph is not a map. In order for an image or drawing to be a map there is a number of different requirements. To be a map there must be a north arrow, a scale bar, a locator map, a watermark that gives credit to the map maker and there should also be a data sources denoted to give credit to the data collector. Without a scale bar an image is just that, an image. The scale bar gives the viewer an idea of the size of the area in the map and allows them to calculate distances. A north arrow obviously shows the viewer the orientation of the map. A watermark is just stating who the maker of the map was and is essential to making sure that no one steals your map and also proves that you did not steal the map.

What can spatial patterns of data tell the reader about UAS data? Provide several examples.

         Spatial patterns of data in UAS have a number of different uses. The viewer can look at topography, watershed analysis, elevation changes and so on. UAS data can be used to view the changes in vegetation as elevation changes. Also UAS could be used to spatially analyze a flood plane of a river in the spring time which can assist in urban planning and public safety.

What are the objectives of the lab?

        There are several objectives to this lab, being able to take UAS data and then manipulate it in GIS software is the first. The next objective is to be able to make maps correctly and accurately with all of the components that make up an accurate map. Another objective is to be able to describe and examine maps just visually and through the attribute table and properties tab.

Methods 

What is the difference between a DSM and DEM?

          The obvious difference here being that DSM stands for digital surface model and DEM stands for digital elevation model. DSM is the surface of the earth and the structures and objects that are on it. A DEM does not include features such as houses, bridges, or any other structures, natural or not. A DTM can be known as the same as a DEM depending on where in the world you live, though a DTM will include linear features.

          A DEM is the continuous elevation, recorded by the z-value, over the surface of the earth with no record of vegetation or non natural features. There are used in fields such as water, land and soil uses. In areas with drastic elevation changes, a DEM can be used to used to see areas that are vulnerable to rock or mud slides and from there areas can be identified as not suitable for living.

           A DSM collects all of the features on earth's surface, including vegetation and structures that were man made. DSM's are modeled in a 3D representation of the earths surface. They are used to figure out where to log, because they can be used to tell what areas of forest are old growth and ready to be logged. They can also be used around important communication infrastructures such as telephone wires to ensure the wires are clear of debris.

What is the difference between a Georeferenced Mosaic and an Orthorectified Mosaic? 

A georeferenced mosaic is attached to a coordinate system. Georefrencing takes a mosaic, which is a raster data set of multiple raster data sets and aligns it with spatial coordinates. This is essential for example because one can take a dated paper map, and scan it and bring it into GIS to be used with modern data.

A orthorectified mosaic fixes distortions of an image that were caused by elevation. It takes into account x, y, and z. a georeferenced mosaic can not be used to measure distance because it does not account for user errors such as the angle the picture was taken, or possible distortion. In contrast a orthorectified mosaic corrects the issues and depicts an accurate display of the surface of the earth. A DEM is needed for this to be done correctly and using ground control points the user can make sure that distances are reflected correctly.

What are the DSM statistics? Why use them?

          When looking at the statistics of the sportfield track DSM, there is a recorded mean value of 20.20, with a standard deviation of 1.04. The data from the DSM has a range of 4.66, the max value is 22.61 and the minimum is 17.95. The spatial reference used was WGS_1984_UTM_Zone_15N. Using the DSM statistics is essential in ensuring data integrity.

Results

What types of patterns do you notice on the orthomosaic? What patterns are noted on the DSM? How do these patterns align with the DSM descriptive statistics? How do the DSM patterns align with patterns with the orthomosaic?

Figure 1

           In the orthomosaic pictured in figure 1 above there does not appear to be any changes in elevation. The middle of the track is all grass, on the east side of the image there is also another grass field. In the south east corner of the track there appears to be an equipment shed with a few tress just to the north. On the west side of the image, just to the east side of the road there is a line of trees. When looking at this image the viewer is able to tell the photo was shot slightly to the south of the track, or the sun was in the southeast corner of the track due to the shadows being cast by all of the protruding features. Also the snow in the southeast corner gives a good idea into the time of the year the data was recorded.

Figure 2

          The DSM of the Eau Claire Sport Track is displayed above in figure 2 with a hillshade overlay. Adding some transparency to each of the layers helps to be able to see the change in elevation and clearly shows the features such as the trees and the shed. The digital surface model above does a great job of illustrating what was discussed about the descriptive statistics. The track slopes from high to low elevation from the northeast portion of the track to the southwest portion.

What anomalies or errors are noted in the data sets? Where is the data quality the best? Where do you note poor data quality?
       
           The sportfield track is located in Eau Claire Wisconsin, therefore the elevation data is not correct. Eau Claire is 240 meters above sea level, and the max value denoted in the data set is 22.61. The change in elevation is 4.66, this is a reasonable change in elevation for track that is used at a middle school and high school level. This elevation change would likely not be noticeable when using the track.


Conclusion 

Summarize what makes UAS data useful as a tool to the cartographer and GIS user.

         UAS data is very useful to any cartographer, and as the field of UAS grows it will be a prominent tool in the field of geography and to be more specific cartography. UAS is a useful tool because data can be taken and then in less than a few hours can be uploaded and maps can be made. This is important to note because the alternative method of taking this type of aerial data with a plane could take weeks to process because it has to be developed from film and then scanned on a high resolution scanner, that process can take over a week. Along with long development times, a plane has to wait for a clear day to fly because they need minimal could cover, whereas a UAV can usually fly well below the cloud cover. UAS is useful for so many different applications, such as search and rescue, disaster assessment, forest and mineral management and much more.

What limitations does the data have? What should the user know about the data when working with it.

          UAS does have some limitations, there are limitations on when, where and how high a unmanned craft can fly. Also as popularity rises there will be more and more regulations to ensure safe operation. At this point there are many inexperienced user out there and it is only a matter of time until something serious happens in relation to striking other aircraft, falling or running into something that it should not. Someone using UAS data should know that it is not a map without geo-referencing and adding the proper criteria to fit that of a map.

Speculate what other forms of data this data could be combined with to make it even more useful.

         Combining UAS data with data such as precipitation, land cover, water sheds, agriculture, soil type and many other data types can be beneficial. UAS can assist in figuring out how rain shadows work on mountains for example. It has also be used to see which area of a field have healthy crops and which areas do not. Also another application would be to take accurate high quality UAS data and overlay active fault lines, to possibly see if the faults are noticeable and to predict where future slips could be.



Sources

• https://en.wikipedia.org/wiki/Digital_elevation_model
• http://gisgeography.com/dem-dsm-dtm-differences/