[TowerTalk] Ain't technology grand?!?

[Jim Lux]

On 3/9/13 6:24 AM, K7LXC at aol.com wrote:
> Howdy, TowerTalkians --
>
>       If you've ever worked with a crane, a  critical distance is from where
> the crane will set up to where the  load is going. In the past you'd have
> to climb roofs or otherwise estimate  sometimes blind distances and hope your
> estimate is a good one.
>
>      I hired a 37 Ton crane today to stand a 60' AN  Wireless tower. The
> operator took out his Verizon Android smartphone and used an  app to help do
> his job. He located the site with a Google Maps-type  view and marked with his
> finger where the crane was going to be set up in  the driveway and where
> the tower base was. He pushed a button and it told  him the distance was 63.26
> feet. Cool. This app - he said it was Map Ruler  - did it easily and fast.
>
>      Being a trailing-edge technology kind of guy, it  was news to me plus
> being nifty and very helpful. I can see it being used to  help site where a
> tower will go, measure trench lengths, distances between  towers for possible
> wire antennas, etc.
>
>      Any other cool apps we'd be interested in out there  for tower, etc.
> stuff?
>

There's a bunch of theodolite type apps for iPhone and Android. They 
seem to be of two kinds.. ones where you point the camera at the item of 
interest and others where you sight along the edge of the case.  More of 
the former now than the latter.

They tell you vertical angle and compass direction, both accurate to a 
few degrees.

Some of the theodolite apps will solve for triangles by measuring 
multiple angles and knowing the distance or size of something in the 
image. (e.g. if you know how long the boom is then you could measure the 
height of the tower by measuring the angular size of the antenna).

In general, measurements of angles made between two things in the same 
image are quite precise (small fraction of a degree). That's limited 
mostly by the camera resolution and the consistency of the optics, which 
is pretty good (500 pixels over a field of view of 45 degrees is better 
than 0.1 degree)

Angle uncertainty of 1 degree is about 1 part in 60 in distance/width 
for small angles.

If you're 100 ft from a tower, and you measure the angle to the top as 
45 degrees, and you have +/-1 degree accuracy, the tower is probably 
somewhere between 96 and 104 ft tall.

A similar device, but much higher performance, are the Leica Disto laser 
distance meters (from about $150 to 400).  They'll tell you how far 
something is 100m or more away with an accuracy of better than a 
centimeter.  The fancier ones will measure the angle, so you can turn 
slope distance into horizontal and vertical distance. (e.g. makes 
measuring the height of a tower or a building trivial)