Wednesday, March 6, 2013

Calculating Line-of-sight and the Quest for internet


We currently live in an area not served by cable or DSL, and our internet options are satellite or microwave internet.  Microwave internet is the best choice for us because of the lower latency in the microwave signal - much better for video conferencing and working with distant co-workers in real time.

Microwave internet works by line-of-sight from a dish at the property in question to a microwave tower.  

Right now Ryan and I are in the process of finding a new place to live, and I check line-of-sight from each place we look at to different microwave towers in the Bitterroot Valley, to make sure that we would have internet coverage if we lived there.

How to Calculate Line-of-sight

To calculate line-of-sight, first locate your point (in this case a house) using hillmap.com.  Make sure you're on the Paths tab on Hillmap.

Click on the map at your first location, and then click on the point of your second location (in this case the microwave tower).  Hillmap will draw a line between the two points.


A path drawn between a house and a microwave tower
The Paths tab is circled in purple, the Profile button is circled in red
Click on the Profile button on the upper left hand of the screen, and a path profile window will pop up, similar to the one below.  The blue graph at the top of the window shows the elevation changes between the two points.


If you have a clear line-of-sight, the graph will not have any big bumps between your two points.  An obstructed line-of-sight will have big bumps between the two points, showing that there are hills in the way.  Hills will block the microwave internet signal.  The graph above shows a pretty clear line-of-sight.




This graph above shows an obstructed line-of-sight.  Of course, this analysis only includes topography and not trees, towers or other obstacles that can block your line-of-sight.  You can check the Satellite map on hillmap.com to see if the location you are looking at has thick tree cover, but a site visit is probably necessary to get a true idea of trees and other obstacles.



This Satellite image shows a thick band of trees on the hill just below the house I'm concerned about, indicating a possible blockage to the line-of-sight.  If the tree tops are low enough, the signal may be able to pass.

6 comments:

Gerald said...

How do you enter the height above terrain of the microwave tower?

Jen Gregory said...

The short answer is, there is no way on hillmap to enter the hight of the tower above the terrain.

If you know the area then calculating the line of sight may give you enough information to know if there's a good possibility of the line of site existing and if it's worth your time to gather more info (go in person to see if line of sight exists, etc.)

Peter Underwood said...

Great info - thanks!

Seems I am missing something here. What's the red graph? There is no scale shown on the vertical axis and I can't find anything in any of the help/blog pages. Thanks.

(By the way, the tower problem is fairly easily solved. If you draw a line from start to end on the profile, that's the line of sight - obstructed by anything that is above it of course. If you take that profile and draw a point on it the height of the tower above that end point then draw the line, some of the obstructions will no longer be above that line.)

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Unknown said...

How do i use line of sight on Google map

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