Viewshed revisited
Plan for next 4 sessions
• Today is more on Viewshed and models
• Thursday is on finding shortest (least
cost) pathway between A and B
• Next Tuesday is Hydrology
• Last class is a summary
• Presentations on 12/13 5 to 7+ in 140
Baker - refreshments provided!
How it is done
1.
2.
3.
4.
Master the GDB way of working
Smooth the DEM
Make a Hillshade of the DEM
Create the viewpoint (observer) FC
a. GDB, Rt Click, New, etc
b. Make sure the projection is correct
c. Edit to make point(s) and edit table
5. RUN Viewshed.
The GDB thing
• The file GDB is faster but the
personal GDB is surer
• Have a Master GDB
• Create project GDBs
• Copy and paste (or drag) the needed
data from the master GDB to the
project GDB
Making the viewpoint
1. Click on the project GDB and select
New
a. Make sure you get the right kind of output
file (POINT, POLY, ETC.)
b. Make sure you have the projection right
c. Create the attribute file fields as the last
step in creating the FC
i.
I used Double for all fields EXCEPT ID (short
integer)
Fields
These fields are inputs
• SPOT – absolute elevation for viewpoint (observer) - use for
airplanes. If the SPOT field is = zero (?) or not present then the
elevation from the DEM is used.
• OFFSETA - Adds an offset or extra height to the elevation at the
viewpoint
• OFFSETB - Adds a constant elevation to all non-viewpoint cells
(unimportant in VISIBILITY analysis)
• AZIMUTH1 AND AZIMUTH2 define the starting compass angle
and ending compass angles. If not there then these values are 0 and
360 degrees
• VERT1 and VERT2 define the angles above and below the horizon
(respectively) to limit visibility. + above, - below
• RADIUS1 and RADIUS2 limit the circles of search. Distances <
RADIUS1 and distances > RADIUS2 are not searched, Creates a
donut of search areas.
These fields are inputs
• SPOT – absolute elevation for viewpoint (observer) - use for
airplanes. If the SPOT field is = zero (?) or not present then the
elevation from the DEM is used.
• OFFSETA - Adds an offset or extra height to the elevation at the
viewpoint
• OFFSETB - Adds a constant elevation to all non-viewpoint cells
(unimportant in VISIBILITY analysis)
• AZIMUTH1 AND AZIMUTH2 define the starting compass angle
and ending compass angles. If not there then these values are 0 and
360 degrees
• VERT1 and VERT2 define the angles above and below the horizon
(respectively) to limit visibility. + above, - below
• RADIUS1 and RADIUS2 limit the circles of search. Distances <
RADIUS1 and distances > RADIUS2 are not searched, Creates a
donut of search areas.
Simple Example
• Simple it may be but it is most
common form of viewshed
• Want to place a TV tower in
Martinsburg to broadcast to folks in
town
• So created a viewpoint with the
following…
Run Viewshed
Oops
Another But
•
•
•
•
•
•
•
Wanted to reach residences
Well, did not do much of a job of that!
So
Made tower higher: 90m
Ran again
Hummm – not real good even at that height
Fix?
Another Problem
• What about trees?
• Make 60 feet or 20m tall
• And?
OK who gets TV?
• How to see how well the tower will
serve the residential properties
• Select by attribute CLS between 200
and jlt 300
• Classify viewshed
• Convert GRID to Poly and make a FC
that is just the residential properties
Now do a…
• Select by Location to find parcels
that ?????
• Intersect?
• Contain?
• Are completely within?
Numbers aren’t great!
• May have to put a repeater in the
valley!
Using the modeler
• Don’t use File GDB – I had lots of
trouble when using the modeler
• In any case you have to be really
careful about naming and when the
results go
• I using multiple tower heights you
can…
Multiple tries
• Easy way is the edit the viewpoint files --Change the height
• I tried copying the tower FC and then
editing it – don’t do it – make a new FC!
• Hard way is to copy and paste the model
into a new model and then change the
output names – ran into all kinds of trouble.
Thursday
• Finding least cost pathways for
traveling between point A and B
• Windfarm at top of Martinsburg
• Get power to one of the substations
– prefer close to roads but not near
existing transmission lines
– Prefer Ag to forest lands
– Don’t like wetlands