- Georeferencing data using the Control Points tool
- Georeferencing an unknown raster image to known vector data
- Interpret residual and Root Mean Square errors
- Digitize building and road features
- Practice polynomial transformations
- Create hyperlinks in ArcGIS
- Create multiple ring buffers
- Overlay data in a 3D environment
First we learned georeferencing in ArcMap. After adding the feature layers and the UWF N and S photos, I noticed that the photos do not line up because the layer didn't come with an accompanying world file. Starting with the north photo and using the Georeferencing toolbar, I fit the photo to the display. To line the image up properly, I used the "Add Control Points" tool. I identified a common point on both the known and the unknown layers and linked the common points by clicking first on the unknown raster image location, then on the known location in the reference data. This shifted the map so that they lined up better. I did this for 10 different points, making sure to spread those points throughout the image. Viewing the links table and the RMS error shows how accurate the data is lining up. The residual value shows how much the link agrees with how the layer is currently displayed; a lower value usually means the control point is more accurately georeferenced. However, if multiple control points are offset by a similar amount, a high residual value could mean a more accurately georeferenced point (it would be an outlier). So, just looking at the residual isn't enough, you need to visually inspect the map as well. The Root Mean Square (RMS) error is a measure of the differences between the predicted values and the actual values, and indicates accuracy of the spatial analysis. After updating the georeferencing, I performed the same process with the southern photo. This photo was more distorted, so the residual error values were different. Additionally, I needed to change the transformation to 2nd order polynomial. A higher order transformation allows the raster to bend and warp more than lower order transformations.
Next we learned about editing. With the Editor tool, we are able to create and edit data. For me, the most important thing to remember about editing is that I have to save the edits or I will lose them when I close the editor or the program. I wanted to digitize the UWF Gym. I started an editing session using the Buildings layer, and chose to create a polygon. I used straight segments to basically outline the perimeter of the building, using many points small distances apart to maintain accuracy. I edited the attribute table and saved the edits. Then I wanted to digitize a UWF campus road. This was basically the same process, except I wanted to digitize along the centerline of the road. I also used the snapping toolbar and enabled edge snapping to snap the ends of that road to the intersecting roads, and saved my edits.
The multiple ring buffer tool was a fairly simple and effective tool. We were given a scenario in which we want to create a new conservation easement for a bald eagle nest on campus property. UWF shows a 330 foot easement already in place around the nest, but the FWC requires a 660 foot protected area. Using the multiple ring buffer tool to show this was quite easy; you just need to input the buffer distances and set dissolve as all (if you want the tool to generate the output as one feature).
Adding a hyperlink is a useful tool to have as well. In an editing session of the Eagle's Nest layer, I edited the attribute table with the student web address using my username, and saved the edits. Then I went into the layer properties, and selected to show the content as a URL.
After all this, I needed to show a map of the UWF campus as well as show the Protection Buffer in an inset. Just zooming in on the buffer layer wouldn't really show where the buffers were in comparison to the campus, so I showed both on my inset map, with a basemap underneath.
Finally, we learned about creating 3D scenes. In ArcScene, I added the feature layers and photos, as well as the DEM. We had an introduction to ArcScene via last week's module in the other course, so I understood what to expect with my output. I selected "Floating on a custom surface" and the DEM layer, and to eliminate the black line between the raster images, I added a layer offset. To get the 3D appearance, I extruded the values by height, selecting "adding it to each feature's maximum height." This way the buildings are kept level. I also changed the vertical exaggeration to emphasize the 3D effect. I exported the scene to 2D, saved it, and added it to ArcMap. From here, I created a map adding the essential map elements, and making sure that the two items I itemized were displayed. I changed the color of the digitized features to red so they can be seen better. That map is shown below. On to the final!
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