Today I was asked to locate and get elevations on some overhead high voltage wires and cable wires and telco wires. The last time I did this was at least 30 years ago and we did the 2-man thing with the rodman on the ground under the wires and shooting vertical angle offsets up to the wires. In 2013 I started using Fieldgenius software and it has some very cool offset and intersection programs. The new one (for me) that I used today is called the Vertical Plane Projection Intersection. You shoot (prism or reflectorless) the insulators at each end of a wire or 2 points on a wall or whatever is connected by 2 points. After that you point the gun at anyplace along the wire (or wall) and hit measure (it uses angles only no distance). The software calcs the 3D intersection between the gun azimuth and vertical angle with the wire (or wall) vertical plane. A one-man operation and it worked like a charm.
The Telco cable was 2+" thick so as a check I did 4 reflectorless stakeout shots to 4 previous VPPI shots on that cable and they were within 0.1' H & V so this 3D intersection seems to be quite good
Isn't sag a factor?
Me. "What's the difference?"
T.C. Carroll "It's the difference between right and wrong!"
Isn't sag a factor?
Only if you just shoot each end and try to calc the sag. Using the Vertical Plane Projection Intersection I shot points every 20-25 feet along the wire and plotted the actual wire profile. Piece of cake with no complicated calcs.
EDIT: Apparently Trimble has a version. Here is a link from Reddit.
Temperature as a factor?
Temperature as a factor?
Out of curiosity, I had to research that.
I wish I hadn't looked at that link. I feel a headache coming on. I'm wondering if the careful work you did had any value unless it included some temperature values such as air temp?
Yeah, the transmission line engineers are going to want the local temperature. I think they often want time of shots in addition to determine load on the lines. If someone is just looking for overhead clearance on distribution lines, it is probably not a critical issue. But it could be if the clearance is tight enough.
I shoot a lot of distribution lines were the cross the track for clearance when working on RR design surveys. Rarely do I shoot the lines for sag. I have seen the railroad require the utilities to raise a pole based on our shots though. If push came to shove, I routinely record the rough temperatures for use in PPM calculations, so I guess
The 2 poles that mattered were only 120 feet apart on each side of a new 2 story ADU where I was setting offsets for construction. I doubt temperature will matter on that short span and it is in a beach city with mild temp changes.
I have learned that Bonneville Power Administration has models of wire heights for their transmission lines. They can provide 3d linework, and don't respect anybody else's survey. They have teams of people and fleet of aircraft monitoring their facilities year round, modelling the sag due to load and atmospheric conditions in real time. I presume that other major electric utilities in other parts of the country do the same.
As for local service wires - I've always been able to simply shoot them reflectorless without difficulty.
Psssst. Catenary is the key word. Spread the word.
Is that short for Cat ate a Canary?
