Topo blunder

Bruce Small · 2017-03-11T18:55:00Z

Last year I did a topo in a parking lot where IÛªve been surveying for 30 years. Everything I did was routine, but something went wrong and parts of the topo are incorrect. I canÛªt see a flaw in anything I did, but something obviously happened.I always follow the same plan. Set the base up, shoot key points including the bench mark with a bipod for stability, remove the bipod, and start collecting. Absolutely standard and IÛªve done it thousands of times.I uploaded the original untouched archived topo file from last year and tried to duplicate what I did. Half the site is torn up, but outside the fence the pavement is untouched. Same as last year, I calibrated on my key boundary monument from 30 years ago, shot a second boundary monument, the bench mark, the PK control points that are still there, and took pavement and concrete elevations. (The PK control points were needed for the later reflectorless shots for the areas under the trees and by the building.)Here is the mystery: Five of the control points I shot last year using a bipod for stability are still there and match todayÛªs shots within 0.03 feet vertically. All of the topo shots I took last year without a bipod are low by 0.45 feet average. All of the reflectorless shots are correct. You could conclude I had accidentally changed the rover rod when I took off the bipod, but I am obsessive about checking the rod height and surely I would have noticed after several hours, and in any case I would never change the rod height a piddly half foot. I have a standard rod height of 5.60 feet for almost everything and make sure the markings face me.The bottom line is I have no idea what gremlins struck, or how.

Summarize Topic

Page 4 / 4 Prev

Strictly Surveying

Last Post by ropestretcher 9 years ago

63 Posts

33 Users

0 Reactions

2,102 Views

RSS

edward-reading

(@edward-reading)

Posts: 559

Member

Translate ▼

Bruce Small, post: 418662, member: 1201 wrote:

Lesson learned, the hard way: Doing everything methodically and carefully every time is not sufficient. There is indeed a reason to check into the benchmark as the last shot of the day.

Not just a benchmark, a 3D control point as the last shot every time. There is a reason it's in Survey 101. Check, check, check.

Posted : March 15, 2017 1:14 pm

Norm

(@norm)

Posts: 1331

Member

Translate ▼

Bad initialization next to a building due to multipath? I know it would never happen with Leica....

Posted : March 15, 2017 1:41 pm

ropestretcher

(@ropestretcher)

Posts: 225

Member

Translate ▼

Did you have to clean bird doo doo off the base antenna that day?

Posted : March 15, 2017 2:43 pm

Page 4 / 4 Prev

26 Forums
54.5 K Topics
592.1 K Posts
259 Online
16.9 K Members

Forum Icons: Forum contains no unread posts Forum contains unread posts

Topic Icons: Not Replied Replied Active Hot Sticky Unapproved Solved Private Closed

Topo blunder

Please support our supporters!

Our Policies

Quick Links

Support