Sarge
Kris Morgan:
Do you use grid bearings or geodetic?
How Would You Do It With A Conventional Traverse ?
Most surveyors do not fully consider the elevation changes on conventional traverses. Many do not even carry elevations on their traverse, so they have no way to even comprehend it.
Using two scale factors means your plane survey is at two elevations, will not work in any software I know.
A survey is one project, use one scale factor. I have also learned to pay attention to the layout of my GPS. On several projects I have had a cluster of GPS points at one end and much fewer at the other. Meaning all scale factors would skew the combined scale factor, so I cherry pick some points.
Paul in PA
> > So, given the above info, and given that I can't be persuaded to reduce my terrestrial measurements to grid, what would y'all recommend as a means of converting these grid values to ground?
>
> Well, the practice that I follow in a situation like that is to use one average Combined Scale Factor for the whole tract to compute surface distances for map and metes and bounds description. In your case, the average CSF = 0.999951 is only about 10ppm off the high and low values you quote. That's an error of 0.05 ft. per mile in absolute terms, which seems fairly trivial for practical purposes.
I realize that I answered a somewhat different question than you asked. In fact, I only use the average Combined Scale Factor to compute surface distances from grid distances when maps are to be annotated and metes and bounds descriptions are to be written. As a matter of practice, I don't do any 2D traverse, but carry elevations/ellipsoid heights throughout the survey so that the reductions to grid can be made essentially exactly when the conventional measurements are adjusted in Star*Net.
More than twenty years ago, I did use a one-size-fits-all CSF when computing traverses over areas where the value of the CSF varied by less than 10ppm, but that fell by the wayside when GPS made extending sufficiently good vertical control to derive exact values of the CSF a snap.
Carlson oops
Wow. This is a pretty good headscratcher. Right up there with the International Feet insert units issue. Thank you for pointing it out!