NCSU GIS/MEA582:
Geospatial Modeling and Analysis

Viewshed and solar radiation analysis

Resources: ESRI Academy

Launch ArcGIS Pro and login with ArcGIS Online credentials if required. Select New> Map> Create New Project. Create a new project in your preferred workspace, in the instructions below we are using the default C:\Users\myname\Documents\ArcGIS\Projects\ folder.

Use your judgement to decide which maps to include in your report.

Viewshed Analysis

Add the raster elev_ned
Add the point feature class fire_pt

Use Viewshed tool (not 'Viewshed 2' or the 'Ready to use tool') to compute the area visible from the fire_pt location.

In the Geoprocessing pane, search for and select the Visibility tool from the Spatial Analyst Toolbox or 3D Analyst toolbox (the tool is listed twice in the Geoprocessing list, but either works).
Set input surface to 'elev_ned'
Set observer feature to 'fire_pt'
Set output raster to 'viewshe_elev1'
Click 'Run'

To see the ground elevation at the fire_pt, find the Export to Point tool in the Geoprocessing list.

Input raster: evel_ned
Input put: our x and y values for fire point
Output rater: fire_pt_elevation

What is the ground elevation at the fire_pt site?
In the output (viewshed) raster the visible cells are given a value of 1, while those not visible are assigned a value of 0.
How many cells are visible in this view shed?
How much area (in sq. meters) do these visible cells represent?

Rerun the viewshed, with elevation offset at the fire_pnt site at +60 m.

Add the field OFFSETA to the fire_pt attribute table.

In the Geoprocessing pane, search for and select the 'Visibility' tool

    Set input surface to 'elev_ned'
    Set observer feature to 'fire_pt'
    Set output raster to 'viewshe_elev60'
    Click the carrot next to “Observer Parameters”
    Under observer offset, input 60.
    Click 'Run'

What is the difference between surface offset, observer elevation, and observer offset?

Now, how many cell are visible in this viewshed?
How much additional area was gained by adding the 60 m of elevation to the observer?

Rerun the viewshed

    In the Geoprocessing pane, search for and select the 'Visibility' tool
    Set input surface to 'elev_ned'
    Set observer feature to 'fire_pt'
    Click the carrot next to “Observer Parameters”
    Under observer offset, input 60
    For inner radius, input 0.
    For outer radius, input 2000.
    Click 'Run'

How many cells are visible in this viewshed? How much ground area is visible?

Restrict the search area to an annulus 1000 m wide (from 1000m to 2000m) and restrict the search azimuth to the arc from NE (45 deg) to SE (135 deg).

    In the Geoprocessing pane, search for and select the Visibility tool
    Set input surface to 'elev_ned'
    Set observer feature to 'fire_pt'
    Click the carrot next to “Observer Parameters”
    Under observer offset, input 60.
    For inner radius, input 1000.
    For outer radius, input 2000.
    For Horizontal Start Angle, put 45.
    For Horizontal End Angle, put 135.
    Click 'Run'    

Rerun the viewshed (see instructions above)

How many cells and area are visible now?

Now let's next add our own data, but instead of a single point, let's add a pair to the project

Here are the the coordinates (in NC State Plane NAD83) for a building on Centennial Campus:

x=638898 and y=224528

And for Jordan Hall on Central Campus:

x=638887, y=225365.

Put these values into a text file (use e.g. Notepad but avoid MS Word). and save the file in a known location (with the extension .txt)
Your text file should look something like this:

X,Y
638898,224528
638887,225365

Load your points to ArcGIS Pro:

In the Map tab, in the Layer group, click 'Add Data'->'XY Point data'
A new tool will open in the geoprocessing pane
browse for your saved .txt file
Set Output feature class to 'xy_points'
Set 'X Field' to 'X' and 'Y Field' to 'Y'
Make sure the coordinate system is correct
Click 'Run'

Run a viewshed on your new data with these attributes. For an observer standing atop the Red Hat Building, what do you think that this view shed result represents?
Can the observer see Jordan Hall on the NCSU Central Campus?
Do you think an observer standing atop Jordan Hall could see his counterpart on the Red Hat Building?

Solar radiation analysis

Compute the incident solar radiation for the summer solstice (day number=172)

In the Geoprocessing pane, search for and select the 'Area Solar Radiation' tool
Set input raster = elev_ned
Set the output raster = ned_solar172
Set the latitude = 35.7716 (~for Raleigh, NC)
Set the Time Configuration to Within a day
Set the Date/Time settings-Day number of year to 172
the remainder of the fields can be left at their default values.
Click 'Run'

Repeat the above steps to generate a incident solar radiation raster for the winter solstice (day number=356).
Note: the computation can take some time.

What are the data units for the resulting incident radiation maps?

Determine the difference in radiation energy between the two solstice extremes by differencing the two radiation rasters just created.

In the Geoprocessing pane, search for and select the 'Raster Calculator' tool
Set output to solar_diff
In the calculator's expression field type:
"ned_solar172" - "ned_solar356"

Change the color ramp to one that emphasizes contrast in the difference raster.
Where do you see the greatest differences in insolation between summer and winter?
Where does the least difference in annual insolation occur?
Do these differences make sense? Explain.