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Measuring power line sags.  

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David Livingstone
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So we are working on a project where we staked some power poles.  The contractor asked us if we could measure the sag in the power lines.  I assume this is for minimum clearance reasons and we need to know the ground elevation and the low spot on the wires.  There are about 48 poles on the project.   I can set control points with our GPS and use a Trimble S5 on these control points.

I'm looking for ideas for the best way to do this.  My original idea would be to do it like I would a water tower over flow.  Turn a vertical angle to it. Problem is the corridor for the power line is fairly narrow, less than 100 feet wide.  Instead of being say perpendicular to the low spot and a few hundred feet away I might be set up near the lines themselves.  I'm not sure if this fact creates a lot of error or not.  I could also maybe setup on a parallel road but that might be between a half a mile and a mile away.

I'm not sure of the exact number but the lines are about 50' high.

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Brian McEachern
Posts: 338
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The most modern way to do would be with a form a LiDar and from the air. A few passes with aerial LiDar and you would have more than enough data, however that may be overkill. Alternately, from the ground, a terrestrial LiDar would probably still be the most accurate measurement tool. Outside of that a good narrow beam reflectorless total station should be sufficient. If it is possible to rent or demo some scanning equipment, now might be a good time to break into a new market. 

 

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Jewel Chadd
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FNG
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@mccracker

 Use a pocket laser measurer

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Brian McEachern
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Joined: 5 years ago

250+ posts
Posts: 338

@jewel-chadd

Or that, but LiDar and Drones are cool! 

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David Livingstone
Posts: 948
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We have scanning equipment within my company.  Hadn't thought of that.

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D Bendell
Posts: 108
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I've done this using the total station shooting reflectorless. Shoot the prism beneath the line at it's lowest point. Turn to the line and shoot it reflectorless. We didn't need to do this 40+ times though. Just a few spots near entrances. Are you sure the client just wants it for clearance? 

How accurate do they want it to be? If they only want clearance information it shouldn't matter if there is a little error? 

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David Livingstone
Posts: 948
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I wasn't sure it would shoot the line reflectorless.  No spec on the accuracy give to me yet.  I would assume nearest foot for something like this.

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