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Compute Inverse

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BurnorMJ
(@burnormj)
10+ posts Member

Hello community,

Question of the day: 

Why does my tsc3 control when I go to cogo and compute and inverse between two points I get X?

When I import into Carlson 2019 and compute inverse between the same two points I get Y?

Example: (#1000 to #1001) COGO in tsc3= 202.891 H. dist; Carlson= 203.50 

Both the drawing and the tsc3 set to state plane coor. system, only difference i can see in the set up is the DC is US survey feet and Carlson is just US feet. Any insight to this would be most helpful.

 

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Topic starter Posted : November 1, 2019 11:43 am
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MathTeacher
(@mathteacher)
1,000+ posts Member

Perhaps the systems have different scale factors. 

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Posted : November 1, 2019 12:06 pm
John Hamilton
(@john-hamilton)
1,000+ posts Member

I would say that one is ground, one is grid or geodetic, but over that short distance you would have to be at 63,000 foot elevation (minus whatever the grid scale factor is). So not that. So my other thought would be one is a slope distance. Or you did a calibration and got some totally whacked out scale factor.  

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Posted : November 1, 2019 12:12 pm

Loyal
(@loyal)
1,000+ posts Member

Agree with John...

Pretty much has to be a "slope distance" or a totally whacked "calibration."

Of course to err is human, to TOTALLY screw things up requires a computer.

GIGO

Loyal

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Posted : November 1, 2019 12:19 pm
sjc1989, FL/GA, oldpacer and 2 people liked
Williwaw
(@williwaw)
1,000+ posts Member

Maybe your data is being scaled once in the DC and again in Carlson? If this is GPS data, maybe post process the vectors for an independent check on the solutions?

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Posted : November 1, 2019 12:31 pm
Bill93 liked
BStrand
(@bstrand)
1,000+ posts Member

Yeah, I'd guess slope distance on one of them.

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Posted : November 1, 2019 12:36 pm

Norman Oklahoma
(@norman-oklahoma)
5,000+ posts Member

I'm with the slope distance v. horiz. distance crowd.

BTW - it isn't really enough to say that you are using a TSC3. That is just a device. It's the software the device is running that is really key.   

 

 

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Posted : November 1, 2019 1:09 pm
MightyMoe
(@mightymoe)
5,000+ posts Supporter

So here's an old timer's question.

What is the correct answer?

Sounds like you have two coordinate pairs, it's simple to calculate by hand. 

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Posted : November 1, 2019 2:00 pm
Trimbleman
(@trimbleman)
10+ posts Member

Try changing your cogo to grid or ground. 

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Posted : November 1, 2019 4:34 pm

GeeOddMike
(@geeoddmike)
1,000+ posts Member
Loyal
(@loyal)
1,000+ posts Member

Another possibility is that "you" (the two different computers) are mixing zones.

Data collector in one zone, desktop/laptop in another.

Just say'n

Loyal

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Posted : November 1, 2019 6:46 pm
David Baalman
(@david-baalman)
100+ posts Member
Posted by: @mightymoe

So here's an old timer's question.

What is the correct answer?

Sounds like you have two coordinate pairs, it's simple to calculate by hand. 

My thoughts exactly, and I'll take it a step further. Take a look at the coordinates in each device to see of they are the same or not. If they are the same, then one or both of them is doing something odd with the inverse. Compute it by hand to see which is screwing things up. If they are different, then one of them is making some sort of a translation, which would merit further investigation.

I for one really hate that much of our software is designed to "fix" things for us like changing coordinates from us feet to international feet based on some obscure Metadata setting, without telling us that it has made the change. It takes 5 clicks to delete a file, but we can move things without trying. Rant off, preaching to the choir anyway. 😉  

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Posted : November 1, 2019 6:47 pm

MathTeacher
(@mathteacher)
1,000+ posts Member

@david-baalman

There's no substitute for eyeballing the data. Just to add to the scale factor consideration, one does not have to be ground and the other grid, the two systems just have to be using different scale factors.

Consider this. Suppose the desired scale factor is 1.0015 and one of the two systems uses the reciprocal of the scale factor instead of dividing to get ground from grid. Both have 1.0015 as the scale factor, but one system uses 1/1.0015 = 0.9985022 for its calculations. 

The ratio of the two results will be 1.0015/0.9985022 = 1.0030023, which is very close to the OP's result. The scale factor that hits OP's numbers exactly under this scenario is 1.001499681.

Anything's possible,right?

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Posted : November 2, 2019 3:39 am
Skeeter1996
(@skeeter1996)
1,000+ posts Member

I ran into the same situation about three years ago. Ran it by the Community, but never got an answer.

My situation was Survey Controller on a TSC2. Compared the inverses between the TSC2, AutoCad LDD, and an HP41 calculator. I got three different solutions using the same coordinates. The TSC2 solution had the biggest difference so I quit trusting it's solutions. Haven't checked out my current TSC3 to see where it stands.

 

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Posted : November 2, 2019 9:51 am
Loyal
(@loyal)
1,000+ posts Member

Is this a GNSS or "Total Station" project (observations).

IF were are talking about a GPS/GNSS situation, then the SIMPLE solution, is to export the Latitude, Longitude, Ellipsoid (or orthometric) height for these (or ALL) points out of the TSC3 (which SHOULD be a piece of cake).

Compute the (your zone) State Plane Coordinates of the points in question (I would use the NGS software to do this), and follow the yellow brick road from there.

The NGS "tool kit" has EVERYTHING you could possibly need to sort this out.

Loyal

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Posted : November 2, 2019 10:02 am

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