Statement of positional accuracy on topographic map

[sako]

Recently I was asked to add a statement of positional accuracy and error of closure limits on my topographic map. I would like to know your opinion and what would you include on the statement.
Thanks

[land butcher]

Did you traverse the boundary? If so what was your closure.

As for locations of topographic features
XY +/- 0.1 ft or greater - your call

z dirt +/- 0.1 or greater

z concrete +/- 0.01

Do the requestees have any clue as to what positional tolerance is?

[Paul Goebel]

Could you just cite the National Map Accuracy Standards? I have done this in the past. The standards are mostly intended for aerial mapping and should be easy to meet with modern equipment.

[Anthony Maffia]

LB:

My comment would be that elevations on hard surfaces, concrete & ac, are +/- 0.03 feet, unless you can show that all of the control points hold together better than that.

I try to avoid such statements, but I'll save DWoolley's note for reference.

[Jim Frame]

"THE COORDINATES SHOWN ARE THE RESULT OF A LEAST SQUARE ADJUSTMENT"

You might want to consider changing "least square" to "least squares," which is shorthand for the method of estimating values by minimizing the sum of the squares of the residuals.


"THE LARGEST STANDARD ERROR BASED ON THE ADJUSTMENT WAS 0.028 NORTHING, 0.025 EASTING AND 0.016 ELEVATION AT ONE SIGMA."

You also might want to consider dropping "at one sigma" as redundant, since the standard error is an estimate of the standard deviation (one sigma by convention). Another thought would be to state the range of the 2-sigma (a.k.a. 95%) errors, since about 1/3 of your points are likely to exceed the 1-sigma value.

.

[TTaylor]

You may want to state your accuracy according to the Geospatial Positioning Accuracy Standards published by the Federal Geographic Data Committee (FGDC) (http://www.fgdc.gov/standards/projects/ ... /accuracy/).

These standards replace the FGCC 1984 and FGCC 1988 standards and are a circular postional accuracy standard. Chpt. 2 deals with standards for Geodetic Networks, Chpt. 3 is the National Standard for Spatial Data Accuracy (NSSDA), Chpt 4. Architecture, Engineering, Construction, and Facilities Management, and Chpt. 5 deals with hydrographic surveys.

[land butcher]

Actually what I meant to say is read to the nearest 0.01ft but 1/2 way thru the typing realized most don't use or have a level rod anymore.

I always put third order level runs on my stuff. dirt read to +/- 0.1 concrete read to +/- 0.01 With trig elevs its a different story.

The biggest problem we have is dealing with those who have no clue. One place I worked the drafter had a plowed dirt field spot elevs on the map to 3 decimal places and could not understand why a water vault was 0.15 below the adjacent sidewalk.

[Anthony Maffia]

Dave - if listing the stations, how about the N & E as published?
And, for grid to ground I prefer multiplication over division, because for some reason people always seem to botch the latter.

I like it. Can we use it?

[RAM]

Do you have redunancy in your measurements?

[RAM]

Good discussion, do I get CE's?

[rmaher]

Dave,

Should you include the elevation used to determine the CF?

I give the NEZ of the point that I used to determine the CF.

8815.5. When CCS83 coordinates are shown on any map, corner record,
or record of survey, a mapping angle, combined grid factor, and the
elevation used to determine the combined grid factor shall be shown
on the map, corner record, or record of survey for at least one
representative point.

Rich

[rmaher]

Also from Post # 10:

ALL COORDINATES SHOWN HEREIN ARE GRID. ALL MEASURED DISTANCES SHOWN HEREIN ARE GRID DISTANCES. TO OBTAIN GROUND DISTANCES, DIVIDE GRID DISTANCES BY 0.99968465


So I wondered: What is the elevation used to calculate "that" CF?

Maybe that is shown on your map. I only had the statement to review.

[rmaher]

I hear you loud and clear. Speaking strictly of my own work, I can't look at the PRC without starting to wonder what else I'm doing wrong.

When I decided to start adding the elevation of the CF to my datum statements I did away with averages and selected a specific point, preferably a monument and gave all information of that.

[sako]

I just want to thank you all for your useful comments.
Too bad we don't have "Thank you" button on this forum.