Terry's GIS Studies and Transition to a New Career

Showing posts with label RMSE. Show all posts
Showing posts with label RMSE. Show all posts

Friday, February 14, 2020

Lab 6--Create a 3D Scene

Again, this portion of the lab built on the two previous products. By downloading a LiDAR layer from the National Map Viewer, I was able to create elevation and relief on the other layers.

To begin, I created a New Local Scene (Insert-New Map Dropdown) and added the LiDAR layer to the scene. In order to smooth the output, I filtered the image by selecting "Ground." I then searched for "LAS Dataset to Raster" in the geoprocessing pane in order to create a digital elevation model (DEM). When the DEM layer was selected, the image appeared to look like terrain features with different colors symbolizing different elevations. In contrast the previous incarnations were more pixelated and reflected off different surfaces.

Once the UWF buildings layer and roads layer were added to the resulting layer, they appeared to be "draped over" the terrain. For this project, I de-selected the DEM layer because I thought the World Elevation 3D/Terrain 3D layer looked better. Once this was complete, I added another layer for a map deliverable. Of course, the map had all essential elements. The only challenge was in rotating the 3D layer so that it was arrayed the way I wanted. There are many ways to do this; however, I went into the properties, and manipulated the degrees of rotation until I liked the result.
The resulting map is displayed below:

Map 3: 3D View of UWF Campus
The above map is the culmination of the entire lab. As stated, all essential map elements are present. The north arrow is arrayed to be the actual magnetic north of the raster layers. If I rotated the map, the north arrow would move in the appropriate direction. The original UWF roads are in red, the original UWF buildings are in light blue, Campus Lane (created feature) is purple, and Building 072 (created feature) is green. The scale bar is in feet because the overall map is in feet. I also added the map data which provides the author/date, sources, elevation ground surface method, and the RMSE and transformation degree.
Week 6--Editing

In the second part of Lab 6, I learned to create a new polygon feature and a new road feature. Though raster layers cannot be edited, new features can be added. This portion of the lab was straightforward and intuitive. To create both features, use the Edit tab, Features group, and click the create button. From there, create the feature desired. One caveat is to be cognizant of shadows on buildings as this could affect the overall size and shape of the building. Once the feature is saved, it appears in the attribute table, where the data can be edited (name, elevation, number, etc.).

The next portion of this lab required the creation of a Multiple Ring Buffer (MRB) to surround an eagle's next at 330 ft and 660 ft. Besides adding the picture to My Google Drive and adding the URL to the attribute table, I created the conservation easement using the MRB. This portion was very easy using the MRB Tool (Analysis tab, Tools, search). The only challenge I had was lining up the numbers in the MRB. I never did get it 100% accurate, but I got it close by using trial and error with the different offsets and array options. The resulting map is presented below:

Map 2: Bald Eagle Conservation Easement Using MRB
The above map was the result of the georeferencing in Part I and the editing of Part II. The main map shows UWF roads in red, Campus Lane (the new road feature created) in yellow, UWF buildings in lavender, and building 072 (the building feature created) in green. The MRB is in the lower right inset with the pink at 330ft and the light green at 660ft. In the main map, I placed a photo inset of the actual nest. To orient the viewer, the inset map of Florida displays Escambia County in red and points to the nest via a callout. The legend displays the different colors, the north arrow is oriented toward map north, and I have included sources, author/date, and the RMSE and transformation used. One lesson I learned through trial and error: You can de-select any feature in the expanded legend feature (content pane) by un-checking the box. This will prevent display of the RGB  boxes.

Week Six Lab--Georeferencing

Part I of this week's lab taught georeferencing. Two UWF (north and south) raster projections were added to the map. Once added, they appeared on "Null Island" off the west coast of Africa until the layers were georeferenced and "knew" their actual location. To move the image from Null Island, I clicked on the "Fit to Display" button. Once the image was located on top of the current layer, I added control points to align the image with the actual map. A few lessons: Spread out the control points, consider the effects of shadows on building geometry, zoom into the layers for accurate control point placement, and place the control point on the unreferenced layer first.

Review the overall Root Mean Square Error to determine how close the points were to the actual location. Remove control points (view the control point table) with high RMSEs to reduce overall RMSE. Then, determine the transformation to use. The higher the transformation level, the more control points (6 for 2d Order Polynomial; 10 for a 3d Order Polynomial) are needed and the more the raster bends.

Another very interesting portion of the lab demonstrated the techniques to place an unreferenced copy of a drawn map. Once I added the survey map (as imagery), I then georeferenced the map to the referenced imagery as before. This was much more difficult because the map was much older, had limited information, and skewed excessively if control points were placed too close (next to each other versus opposite sides of the image).

Heritage Hall Georeferenced
The above image is the result of georeferencing a parcel survey and then placing it on a UWF Campus image. The control points are shown in red (parcel survey) and green (image) and the overall RMSE was 6.770932. The most efficient way to place control points was to use the edges of parking lots and the points of medians, since no buildings were drawn on the parcel survey. Again, place control points on opposite ends of the image (much like you tighten lug nuts on a tire) to reduce distortion.