Assignment 2: Building Maps with Pix4D

Introduction:

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

Being able to understand not only the information associated with what the viewer is looking at, but also the context of that information is crucial to understanding a map. This puts emphasis on the cartographer to ensure that the map is easily understood by anyone analyzing it.

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

All maps must include a scale, a north arrow, watermark, locator map, and data sources. These are all important features each map should contain for proper understanding and analysis.

What can spatial patterns of data tell the reader about UAS data?

Using a UAS to collect data can be very beneficial to projects or research that requires a more customized analysis that can be more cost effective, more timely, and more accurate than using satellite imagery. Using UAS imagery can help the viewer to analyze spatial patterns on the earth's surface. These could include crop yields and the soils associated with certain areas, mountain ranges and where fault lines are located, city planners and where people live, work, and travel, and the list goes on.

What are the objectives of this lab?

The objectives are to become familiar with ArcScene and ArcMap, as well as work on good map-making techniques, and using a variety of UAS processed imagery.

What is the difference between a DSM and a DEM? A georeferenced mosaic and a orthorectified mosaic?

A DSM shows the elevation of earth's surface and the objects on the surface. A DEM only shows the elevation of the ground, excluding vegetation, buildings, and any other non-surface extremities. 

A mosaic is a collection of images that are placed on top of one another to create a unified image of the earth. A georeferenced mosaic already has a coordinate system attached to it and has information on which coordinate system it is in, so it can be modified for other coordinate systems. An orthorectified mosaic is an image that has been manipulated to fit into a specific coordinate system and minimizing the distortion to the image because of this. 

Methods:

The images used to make these maps were collected by a DJI Phantom drone from a height of 50 meters at a track in Eau Claire, WI. From there, the images were brought into ArcScene and ArcMap as hillshade, digital surface model, and orthomosaic rasters. These were then used to create three separate maps, each one displaying different information of the same location. The first map shows an image of the track that is an orthorectified mosaic rendering; meaning the image has coordinates attached to it, giving the image a geographic location. This is evident through out all three maps, as they all use a basemap which is rendered in accordance with the coordinates from the images. The second map is a digital surface model (DSM) which is an image that shows elevation of the earth's surface and objects on the surface. The third and final map is a hillshade DSM, which helps visualize the surface elevation using shadows.

Results:

Looking at the maps, there are some fairly interesting patterns that are visible. Looking at the DSM, there is an elevation gradient from the northeastern portion of the field to the southwestern portion. This accounts for a fairly gradual slope in the surface, which isn't ideal for a track, however, it's more than likely not very noticeable. Looking at the hillshade map, the area within the outermost lane of the track is quite flat, which is to be expected. Off the track and field, however, there are some patterns that could reflect areas of water drainage and other uneven surfaces as well as some vegetation and a man-made structure. 

Conclusion:

Using UAS imagery, the viewer can get a good sense of different patterns and occurrences happening at the ground level. The three maps that were made for the context of this assignment were helpful in noticing the slope of the field from the DSM, which wouldn't be easy to do just looking at the original image and would have to be done by surveying the land. Also looking at the evenness of the land is made easy by using the hillshade image. Combing the maps together, to form one map with different layers could be more useful than the methods used here, as it would allow for a greater exaggeration of the irregularities of the surface. 

Sources

http://gisgeography.com/dem-dsm-dtm-differences/

https://imageryspeaks.wordpress.com/2012/01/24/georeferencing-vs-georectification-vs-geocoding/