Raster Analysis in ESRI Tutorials with ArcGIS Pro

We are going to engage in a series of tutorials created by ESRI for ArcPro. These are designed to serve several forms of raster data analysis. We will be seeing how you can use DEMs, DTMs, or DSMs for various forms of analysis such as calculating slope and aspect. Then we will do some other tutorials that show how one can calculate line of sight and viewshed analysis. As we complete these tutorials, it's important to think of how what were doing could apply to both working with UAS data and in mission planning with UAS. Or even how these forms of analysis could relate to aviation management and safety. We are going to engage in three different ESRI tutorials.

Terrain Analysis using ArcGIS Pro:

When you are analyzing a mountain, an elevation surface is useful for answering the question, "How high?" But what if you want to know "how steep?" or "facing which direction?" What if you want to see what the mountain looks like or determine what you would be able to see from the top of it? Being able to answer these types of questions is useful for many purposes, such as finding potential sites for a ski resort or a wind power turbine. Slope is a measure of steepness. For an elevation surface, slope is related to the difference in elevation between a cell and its neighboring cells. Areas where the elevation changes rapidly have a steeper slope than areas where the elevation changes more gradually. Slope is calculated as the maximum rate of change in values between each cell and its neighbors. Slope may be expressed either as degrees or percentages.

Figure 97: Slope Visual

Aspect is a measure of down-slope direction. If you stand on a slope and walk downhill, the direction you walk will tell you the aspect of that slope. Aspect is a useful measurement for analyzing the impacts of atmospheric phenomena, such as sunlight or prevailing winds. For example, north-facing slopes may make better ski runs, and west-facing slopes near the California shoreline may be more likely to receive cool onshore breezes. Aspect values are measured clockwise in degrees from 0 to 360. The numeric values can be related to directions on a compass, cells facing directly east will have a numeric value of 90 degrees. If you classify the compass into eight directional ranges, then east-facing cells are the cells with values between 67.5 and 112.5. North-facing cells will have values ranging from 0 degrees to 22.5 degrees and 337.5 degrees to 360 degrees. Flat areas are assigned an aspect value of -1.

Figure 98: Aspect Visual

We will now be working with actual data in ArcGIS. We are going to play the role as a GIS specialist that was contracted to produce raster data that is useful for locating potential sites for a vineyard in the San Diego, California, area. You have been provided some initial criteria stating that potential sites must meet the following criteria:

Elevation above 200 meters (656 feet)
Slope between 1.5 percent and 15 percent
Some southern exposure (southeast, south, or southwest)

In this exercise, we will derive slope and aspect surfaces from an elevation surface. You will then perform a preliminary analysis to identify potential vineyard sites that meet the criteria. This preliminary analysis will help narrow down areas of interest for more advanced suitability analyses.

Download the data and open it in ArcGIS
From the Analysis tab, in the Geoprocessing group, click Environments.
In the Environments dialog box, set the following parameters:

Current Workspace: terrainpro.gdb
Output Coordinate System: sd_elevation (NAD 1983 State Plane California VI FIPS 0406 Feet)
Processing Extent: Set Extent to Same As Layer sd_elevation.
Raster Analysis: Set Cell Size to Same As Layer sd_elevation.

Click Ok to save the changes

Now that we have the environment set, we can now create our slope analysis

From the Geoprocessing pane, search for "Slope"
Click Slope (Spatial Analyst Tools) to open the tool, and then set the following parameters:

Input Raster: sd_elevation
Output Raster: ..\p20\terrainpro.gdb\sd_slope

The Output measurement parameter has two options. The Degree option produces slope values in degrees, while the Percent Rise option produces slope values as percentages. We are going to use percent rise. The horizontal units are feet, and the vertical units are meters.

Click Run

Figure 99: Slope Raster Over San Diego

In this next step, we will derive an aspect surface from the elevation surface. We will use this aspect surface later to find terrain with a south-facing slope.

Search for "Aspect"
Open Aspect (Spatial Analyst Tools) and set the following parameters:

Input Raster: sd_elevation
Output Raster: ..\p20\terrainpro.gdb\sd_aspect

Click Run

Figure 100: Aspect Raster Over San Diego

In this next step, we will perform a binary suitability analysis to identify potential vineyard sites. A binary suitability analysis is one method for identifying areas that meet specific criteria. As the criteria are applied to each cell, a cell will be assigned a value of 1 or 0. This method is a relatively simple method for analyzing suitability, but the yes/no nature of a binary analysis obliterates subtle variations in the input layers and produces an oversimplified result. An overlay analysis provides more robust methods for applying criteria and combining inputs to find suitable areas.

From the Geoprocessing pane, search for raster calculator
Open Raster Calculator (Spatial Analyst Tools)

We will start by building an expression for the first criterion: Potential sites must be above 200 meters (656 feet) in elevation.

In the Raster Calculator dialog box, complete the following tasks:

Under Rasters, double-click sd_elevation to add it to the expression box
Under Tools, double-click the greater than button (>) to add the operator
At the end of the expression, type 200
Surround your expression with parentheses

Double-click the ampersand button (&) to add the operator to the end of your expression
After the ampersand, add expressions for the following criteria:

sd_slope must be greater than or equal to (>=) 1.5 percent
sd_slope must be less than or equal to (<=) 15 percent

Add two more parenthetical expressions to apply the third criterion

Your code should look like this:

("sd_elevation" > 200) & (sd_slope" >= 1.5) & ("sd_slope" <= 15) & ("sd_aspect" >= 112.5) & ("sd_aspect" <= 247.5)

Click Run
From the Contents pane, right-click sd_PotentialSites and choose Symbology.
From the Symbology pane, under Values, set the following parameters:

Cells with a value of 0: No Color
Cells with a value of 1: Red

Turn off all layers except the sd_PotentialSites and Topographic basemap layers
Zoom to the La Mesa bookmark

Figure 101: Binary Suitability Analysis of San Diego.

For the second half of this tutorial we will be deriving and using a hillshade surface. Hillshading is a technique used to create a realistic view of terrain. Hillshading shows what a surface would look like when illuminated by a hypothetical light source. The position of the light source in the sky is specified using two parameters:

Azimuth: The direction of the light source. Like aspect, azimuth is measured in degrees starting from 0 (north) and increasing in a clockwise direction so that 90 places the light source to the east, 180 places it to the south, and so on.
Altitude: The angle of the light source above the horizon. The minimum altitude of 0 degrees puts the light source on the horizon, while the maximum altitude of 90 degrees places the light source directly overhead.

After the light source's location has been specified, the hillshade algorithm uses slope and aspect to determine how brightly each cell in the input elevation raster would be illuminated. The brightness values in the resulting hillshade will range from 0 (darkest) to 255 (brightest).

Figure 102: Hillshading Visual

Download the data and open it in ArcGIS
From the Analysis tab, in the Raster group, click Raster Functions
From the Raster Functions pane, expand the Surface group, and then select Hillshade
Under Hillshade Properties, for Raster, choose lm_elevation
Set the Altitude to 40 degrees above the horizon
If necessary, for Z Factor, type 1
Click Create New Layer

In order to make the elevation easier to see and interpret, we can change the color scheme.

Select the lm_elevation layer, and then click the Appearance tab.
From the Appearance tab, in the Rendering group, click Symbology to open the Symbology pane.
Select the Elevation #1 color scheme.

Next, we will combine the coloring effect from the elevation surface with the illumination effect of the hillshade surface. The easiest way to combine the effects of the two layers is using transparency.

From the Appearance tab, set the transparency of the lm_elevation layer to 50%

Figure 103: Hillside Elevation Surface

The potential sites and Murray Reservoir are both visible on the map, but it is difficult to determine which sites have a good view of the reservoir. We will create a viewshed raster to help visualize these views.

From the terrainpro.gdb, drag the Murray_Point feature class onto the map
Open Viewshed (Spatial Analyst Tools) and set the following parameters:

Input Raster: lm_elevation
Input Point Or Polyline Observer Features: Murray_Point
Output Raster: lm_viewshed
Z Factor: 1

Click Run

The lm_viewshed raster is generated and added to the map, obscuring the hillshade and elevation layers beneath it. we could use the Raster Calculator to perform another binary analysis to find potential sites with a view of Murray Reservoir. Instead, we will adjust the viewshed's symbology to help the vineyard owner visually identify sites with the desired view.

Adjust the lm_viewshed layer's symbology:

Change the color of the visible cells to Solar Yellow
Set Transparency to 30%

Figure 104: Contour Lines At Specific Elevations

Now the terrain analysis is complete, with the visible areas identified amid the previously identified locations. The last step is to display the results in a dramatic and visually interesting scene. ArcGIS Pro allows both 3D and 2D scenes to be viewed simultaneously.

From the Contents pane, right-click Visualize_3D and choose Properties
Click the Coordinate Systems tab
In the search field, search for coordinate system WKID code 103008
Select the NAD 1983 (2011) StatePlane California VI FIPS 0406 (US Feet) coordinate system
Click OK.
Right-click the Visualize_3D map tab and choose New Horizontal Tab Group.

The map and the scene are displayed together


Figure 105: 3D Scene Linked To 2D Scene



Performing Viewshed:
    The visibility tools in ArcGIS Pro include many different tools to model the visibility of the horizon, shadows, and line of sight. The Viewshed tool creates an output that models the areas that are visible from given vantage points. By default, the tool considers all possible visible areas within the input raster provided. We will learn how to modify the input features to model the visibility from a known vantage point. Now our analysis can contain a viewshed from fixed vantage points, and we can evaluate the visibility of the entire area.

Download the data and open it in ArcGIS
Review the feature classes that this geodatabase contains
On the Map tab, click Basemap  and choose Streets to change the basemap
Add the PropertyBoundary feature class to the map so that you can see the analysis area
On the Appearance tab, click Symbology 
In the Symbology pane, click the current symbol
In the Format Polygon Symbol pane, click Properties, and then specify the following parameters:
Color: No Color
Outline Color: Mars Red (row 3, column 2)
Outline Width: 2 pt
Click Apply
From the Catalog pane, add the remaining geodatabase feature classes to the map.
In the Contents pane, organize your data so that the layers are arranged in the following order:
LightLocations
PropertyBoundary
NY_DEM
World Street Map (the Streets basemap)
    Now that our data has been added to the basemap, we can begin our analysis. We will modify the LightLocations layer to reflect the lighting capabilities of the new lights. We will add the proper fields and populate them with the appropriate values.
In the Contents pane, right-click the LightLocations layer and choose Attribute Table
In the attribute table, click Add to add a field
    The Fields view opens, and the Fields tab opens on the ribbon. The Fields view shows the content and format for each field in the LightLocations attribute table
For Field Name, type OFFSETA
    The OFFSETA field will affect the height from which the viewshed will be created. It is a vertical distance in surface units to be added to the elevation of the observation point
Add the following additional fields to the field view:
AZIMUTH1
AZIMUTH2
RADIUS2
    The values are based on the capabilities of the lights. Per the lighting company, the light generates illumination out to a distance of 400 meters, and each light illuminates a 100-degree swath. The lights can be pointed in any direction, but the azimuth settings in the table have been specified to reflect the 100-degree angle of illumination based on their locations within the campground. We will use figure 106 to help update the values in the LightLocations attribute table.

Figure 106: LightLocations Attribute Table

Click Yes to save all the edits and close the attribute table
    In the next step, we will create a viewshed to model the new lighting scheme. The results of the viewshed will show the area covered by each light and illustrate which areas are covered by more than one light.
In the Geoprocessing pane, in the search field, type viewshed
Click Viewshed (3D Analyst Tools), and then specify the following parameters:
Input Raster: NY_DEM
Input Point Or Polyline Observer Features: LightLocations
Output Raster: ... Viewshed_3m
Check Use Earth Curvature Corrections Box 
Click Run 
Figure 107: Viewshed 3D Analysis

    In this step, we will use raster functions to model which part of the campground is illuminated by more than two lights.
On the Analysis tab, in the Raster group, click Raster Functions
In the Raster Functions pane, expand Math: Logical
Click Greater Than
In the Greater Than Properties pane, specify the following parameters:
General tab
Output Pixel Type: 8 Bit Unsigned
Parameters tab
Raster: Viewshed_3m
Raster2: 2
Click Create New Layer
    In the next step, we will modify the fields in the LightLocations attribute table to alter the height of the lights, increasing their coverage of the campground.
In the Contents pane, right-click LightLocations and choose Attribute Table
In the attribute table, right-click OFFSETA and choose Calculate Field
In the Calculate Field dialog box, specify the following parameters:
Input Table: LightLocations
Field Name: OFFSETA
OFFSETA = 10
Click apply, and then click Ok
In this final step, we will perform a viewshed analysis with the new values and evaluate the results
In the Recent section, click the Viewshed (3D Analyst Tools) tool
In the Viewshed pane, specify the following parameters:
Input Raster: NY_DEM
Input Point Or Polyline Observer Features: LightLocations
... Viewshed_10m
Check Use Earth Curvature Corrections Box 
Click Run 
Figure 108: Model Light Schemes With New Values



Perform line of sight analysis:
    A line of sight calculates intervisibility between the first vertex, the observer, and the last vertex, the target along a straight line between the two. A line of sight considers any obstructions provided by a surface or multipatch feature class. Visibility between these points is determined along the sight line. Line of sight determines whether two points in space are intervisible. If the terrain hides the target point, one can use line of sight to determine where the obstruction is and what is visible and hidden along the line of sight. 
  
    Imagine that we need to plan security operations for a parade route. How would you place surveillance cameras in strategic locations and position officers on rooftops and other high vantage points to observe crowd behavior? The world is three-dimensional, roads go up and down, and hills and buildings have shapes, heights, volumes, and complex interior infrastructures. We are challenged to map, understand, and analyze the world in three dimensions. Many 3D applications such as planning security operations for a parade route, building shadowing, visualizing potential changes in a landscape, and performing storm water runoff studies are becoming more common.
Download the data and open it in ArcGIS
    We will create lines between each of your observer points and the parade route, spacing these lines 30 feet apart along the parade route
On the Analysis tab, in the Geoprocessing group, click Tools
Use the search function to find and open the Construct Sight Lines (3D Analyst Tools) tool.
In the Geoprocessing pane, set the following parameters:
Observer Points: Observers
Target Features: ParadeRoute
Output:... SightLines
Observer Height Field: SHAPE.Z
Target Height Field: SHAPE.Z
Sampling Distance: 30
Click Run
    After the tool has run successfully, the new SightLines layer is added to the Contents pane. You can zoom in to the lines generated in the image, which displays many lines leading to the parade route. 

Figure 109: Construct Sight Lines


    Next, we will determine the visibility between the observer points and the parade route along each of the sight lines that you created in the previous step
In the Geoprocessing pane, perform the following tasks:
Click the Back button to return to the search function
Use the search function to find the Line Of Sight tool
Set the following parameters:
Input Surface: Elevation
Input Line Features: SightLines
Input Features: Buildings_subset
Output Feature Class: ...LOS_Lines
Click Run
    The next step is removing the sight lines. We will remove those lines of sight that are obstructed from viewing the parade route or that offer views that are too distant. In clear weather, 1,100 feet is the maximum distance to use for analysis.
On the Map tab, in the Selection group, click Select By Attributes
In the Select By Attributes dialog box, set the following parameters:
Input Rows: LOS_Lines
Selection Type: New Selection
Under Expression, click New Expression
Set the parameters to Where TarIsVis Is Equal To 0
Click Add Clause
Set the parameters to Or Length3D Is Greater Than 1100
Click Apply, and then click OK
In the Geoprocessing pane, find and open the Delete Features (Data Management Tools) tool
For Input Features, choose LOS_Lines
Click Run
Figure 110: After Sight Lines Above 1,100 Removed

    One problem faced in surveillance is reduced visibility due to atmospheric conditions, such as rain, fog, and smog. In this step, you will repeat your visibility analysis of the parade route, assuming a maximum visibility of 600 feet. A model has been created to automate the tasks performed in the previous steps.
From the Project tab, click Open, and then click Open Another Project
In the Open Project dialog box, browse to ...ProLineSight and double-click LineOfSightAnalysis.aprx to open it
In the Catalog pane, expand Folders, and then browse to ...VisibilityAnalysis.tbx.
Right-click the Parade Route Visibility model and choose Edit
    The model opens in the ModelBuilder view. The model contains the same tools that we used earlier in our analysis. The model also contains data elements, which are the inputs and outputs for the tools. The tools work the same in the model as they do when you run them from the Geoprocessing pane. The only difference is that in the model, the tools have been connected together so that the output of a tool is the input to the next tool.
This time, the visibility distance excludes the lines of sight that are longer than 600 feet
If necessary, to see the model clearly, on the ModelBuilder tab, in the View group, click Fit To Window
In the ModelBuilder view, double-click Expression To Select LOS Lines
The expression reads Where "TarIsVis" Is Equal To 0 OR "Length3D" Is Greater Than 600
Close the expression box
On the ModelBuilder tab, in the Run group, click Validate
Click Run
Figure 111:Visibility Distance Excludes Over 600ft