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Distance between two NGS marks in SurvCE
Posted by rfc on April 23, 2016 at 10:15 pmPreparing for some more astro; Decided to put the two NGS marks I’m using (setup on one, backsight to another), into SurvCE.
Took the coordinates from the data sheets. DC is set up using “USA/NAD83/VT”, and US Survey FeetWhen I do an inverse on the collector between the two, The AZ is OK (3552702), which is 0103.2 off (Convergence from the data sheet is 103.1), but I took the Horizontal distance from the DC (2764.9114′), and the Vertical Distance (3′)…calculated the Slope Distance to be 2764.91303′, which is 842.96 meters.
The Inverse3D output says it should be 842.8015 meters.
Shouldn’t these be the same?
bill93 replied 8 years, 3 months ago 7 Members · 13 Replies 
13 Replies

are your total station numbers Grid or ground? In Survce under equip, localization, ts, you can select auto scale to grid on the active system. Anyway, you can scale the ground distance down to the grid and check it.

Adam, post: 369054, member: 8900 wrote: are your total station numbers Grid or ground? In Survce under equip, localization, ts, you can select auto scale to grid on the active system. Anyway, you can scale the ground distance down to the grid and check it.
That screen (which I haven’t looked at in ages) says:
Scale=1.000000
The only options to check are “Curvature and Refraction”, and “Sea Level Correction”.
Is that what it should be? 
rfc, post: 369057, member: 8882 wrote: That screen (which I haven’t looked at in ages) says:
Scale=1.000000
The only options to check are “Curvature and Refraction”, and “Sea Level Correction”.
Is that what it should be?Scale equals one will use the distances from the gun with no scaling. So your total station measurements are ground. Average the Combined factors from your two NGS datasheets and apply to the distance.

Adam, post: 369067, member: 8900 wrote: Scale equals one will use the distances from the gun with no scaling. So your total station measurements are ground. Average the Combined factors from your two NGS datasheets and apply to the distance.
No gun in play yet.
I took the Mark to Mark Distance from the Inverse3D sheet: 842.8015 meters. I put the SP coordinates from the same sheets into the DC, and did an inverse: 842.96 meters. That’s .15 meters off. Applying the average combined scale factor for SPC (.999935345), gets me down to 842.9055, but that’s still a tenth of a meter off. Too big. Doing something wrong. 
rfc, post: 369072, member: 8882 wrote: No gun in play yet.
I took the Mark to Mark Distance from the Inverse3D sheet: 842.8015 meters. I put the SP coordinates from the same sheets into the DC, and did an inverse: 842.96 meters. That’s .15 meters off. Applying the average combined scale factor for SPC (.999935345), gets me down to 842.9055, but that’s still a tenth of a meter off. Too big. Doing something wrong.rfc,
Could post the NGS PID of the points?
Loyal

rfc, post: 369072, member: 8882 wrote: No gun in play yet.
I took the Mark to Mark Distance from the Inverse3D sheet: 842.8015 meters. I put the SP coordinates from the same sheets into the DC, and did an inverse: 842.96 meters. That’s .15 meters off. Applying the average combined scale factor for SPC (.999935345), gets me down to 842.9055, but that’s still a tenth of a meter off. Too big. Doing something wrong.The Invers3d program takes account of the 0.9m difference in elevation. SPCS coordinates are 2D. Use the NGS program Inverse (does NOT account for heights) if you want or just the square root of the difference in Northings^2 + difference in Eastings^2. You don’t even need a software package, a calculator will do.
HTH,
DMM

In his other thread the were identified as AA8188 snf AA8189.
. 
SPC coords inverse 842.741 m grid dist.
gulf stream to pom school. 
I computed the plane coordinate inverse and compared the results from the NGS INVERSE and INVERS3D tools.
My summary in meters follows:
INVERS3D output using geodetic coordinates (Lat, Lon and eht) = 842.7765 ellipsoid
INVERSE output also using the geodetic coordinates as above. = 842.7767 ellipsoid heightThe difference between the two measurements is the inclusion of ellipsoid heights in the 3D version.
INVERS3D output also provides a mark to mark distance which is 842.8015 which accounts for the height differences.
Computing a plane coordinate inverse on my iPad yields a grid distance of 842.747
Applying the mean combined factor ( 0.99993536 ) yields a ground distance of 842.802 which agrees with the mark to mark distance.Now I do not know the precision of this iPad app but given the short distances involved it should be fine.
The SPCS values, in VT meters, I used were from the NGS datasheets (AA8188 and AA8189). I used the published combined factors and applied the simple mean. Converting a grid distance to ground involves dividing the grid distance by the combined factor which consists of the scale and elevation factors.
Now I am still in Paris (France not Texas) and having my usual time zone adjustment issues. I did check my inputs and am confident of their correctness though I would prefer to have shown my work but cannot using this iPad.

rfc,
You stated above:
“When I do an inverse on the collector between the two, The AZ is OK (3552702), which is 0103.2 off (Convergence from the data sheet is 103.1), but I took the Horizontal distance from the DC (2764.9114′), and the Vertical Distance (3′)…calculated the Slope Distance to be 2764.91303′, which is 842.96 meters.”
Are you carrying that “842.96” value into your later post?
2764.91303 / 3.2808333333… = 842.747 meters (which agrees with the SPC [meters] inverse).
2764.91303 /842.96 = 3.280005018 and 2764.91303 x 3.28 = 842.961m
Are you sure you haven’t made a simple error, and are carrying forward?
Go through GeeOddMike’s post carefully, he pretty much spelled it out.
Just a thought,
Loyal 
Spot on. Was coming up with my own conversion (feet to inches to meters).
Add “SPC meter to survey feet /intl feet conversions” to my growing reading list. Thanks. 
Depending on which state you are in you need either tthat ratio or the one based on 2.54 cm per inch (international ft)
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