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. Master the GDB way of working2. Smooth the DEM3. Make a Hillshade of the DEM4. Create the viewpoint (observer) FC

a. GDB, Rt Click, New, etcb. Make sure the projection is correctc. 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 rightc. Create the attribute file fields as the

last step in creating the FCi. 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