Closure report

Discussion of MicroSurvey CAD related issues and questions.

Moderators: Brian Sloman, Jason Poitras, James Johnston

Closure report

Postby T.M. Moretz » Fri Nov 12, 2004 9:10 am

I'm using MSCAD 2002. After generating a closure report it reads that there are 12 instrument set ups and 5252.09' of traverse. I like to connect these traverse points with lines. After connecting these points the program tells me the total length of lines drawn. It indicated that I had just drawn 6812.32' of line. This 1560.2' +- difference is the distance of the back sight (same as the closing distance). Am I to understand that neither the BS nor closing distance is taken into consideration when calculating closure? I can see how it calculates angular error but how can it calculate the linear error without a closed polygon created by the distances? The MSCAD closure report indicates an error of 1':15,367' but if I include the missing distance I have an error of 1':21,000'+. This is significant. It seems to me that shorter BS distances would be better for closure!?
Ted
T.M. Moretz
 
Posts: 79
Joined: Fri Nov 08, 2002 1:31 pm
Location: North Carolina, USA

Closures

Postby Glen Cameron » Fri Nov 12, 2004 9:50 am

Here is a simple example that I hope will clarify for you what happens:

The closure distance is measured between the last setup and the original BS point, in this closed loop example.
The total traverse length does not include the original BS shot or the last forsight shot.

Starting Pt:194 Ending Pt:197 Type C

Starting BS bearing: N01°19'17"W Ending FS Bearing: S01°19'17"E
From Pt Angle Distance To Pt
194 91°19'17" 100.000 195
195 90°00'00" 100.000 196
196 90°00'00" 100.000 197
197 90°20'38" 99.682 198

Closure Report:
Current Closing Point vs True Closing Coordinates:
Current Closing North: 36.835
Current Closing East : 933.611
Actual Closing North : 36.494
Actual Closing East : 931.313
Distance Error : 2.324

Closure Ratio 1: 129
Total Traverse Length: 300.000
Closure Direction : S81°33'57"W
Angular Error : 1°39'54"
Error Per Angle : 0°24'59"
Last edited by Glen Cameron on Wed Jun 08, 2005 11:44 am, edited 1 time in total.
Glen W. Cameron, C.E.T.
City of North Bay, Ontario
Glen Cameron
 
Posts: 1395
Joined: Fri Nov 08, 2002 12:18 pm
Location: Corbeil, Ontario, Canada

Closure

Postby T.M. Moretz » Fri Nov 12, 2004 11:29 am

Yes Glen, your example seems to be similar to mine in that it uses one less distance than the number of sides of the traverse and I'm sure that the routine does this by design. THIS is what I don't understand. Why would MicroSurvey not use one of the distances of a polygon to calculate the precision of that polygon? I have always thought that the ratio of precision was calculated by adding the total length of the lines (traverse - polygon) and dividing this total by the distance between the BS point and the last setup point OR dividing by the total traverse distance by the distance between the first setup point and the closing point. This is the method that I prefer even if it means I will need to do it manally. As I mentioned in my first post, MicroSurvey's closure method lends itself to me having a short BS distance and I don't think this proper. I have spent my entire career avoiding short traverses, both backsight and foresight. I think that in my example I have shown what I think is a problem with Microsurvey's method. That's my two cents worth. Ted
T.M. Moretz
 
Posts: 79
Joined: Fri Nov 08, 2002 1:31 pm
Location: North Carolina, USA

Postby rwhatman » Sun Nov 14, 2004 9:47 pm

When I first looked at this Closer I thought that yes the traverse lenght was report wrong. Then I thought about it some and I now believe the program reported the traverse lenght correctly.

This closed loop started with a Backsite and ended with a Foresite.
Two side shots.

There should have been five setups for the traverse closer.

Here is a true closed loop and you will see that it reported the traverse lenght correctly.


Starting BS bearing: N00°00'00"E Ending FS Bearing: N70°30'00"E
From Pt Angle Distance To Pt
1030 340°30'00" 200.000 1031
1031 270°00'00" 300.000 1032
1032 270°00'08" 200.246 6
6 269°54'29" 300.041 5
5 0°00'00" 300.041 6

Closure Report:
Current Closing Point vs True Closing Coordinates:
Current Closing North: 10141.900
Current Closing East : 10357.390
Actual Closing North : 10142.590
Actual Closing East : 10357.197
Distance Error : 0.717

Closure Ratio 1: 1394
Total Traverse Length: 1000.287
Closure Direction : N15°39'27"W
Angular Error : -0°05'23"
Error Per Angle : -0°01'05"

Yes you just had to add one setup point.
The program adds the lenght between setups and not side shots for traverse lenght.

I may be wrong, but this is how the traverse program seems to work.
rwhatman
 
Posts: 299
Joined: Sun Nov 10, 2002 6:41 am
Location: Peterborough, Ontario, Canada

Closure

Postby Ted Moretz » Mon Nov 15, 2004 5:55 am

Richard, even though the BS and foresight shots are sideshots, one of them is needed to complete the polygon. In my example, or any for that matter, what if I'm occuping the BS and getting ready to tie in to nail 1 and I turn a good angle but the distance I shoot is off because of whatever reason - the instrument shoots a window or reflective street sign in the background (stranger things have happened), would the closure routine catch this or would I need to find this manually? I don't doubt that the program is doing what it is designed to do, I just don't understand why it's doing it this way. All of the examples of a closed loop traverse in MicroSurvey show a closed polygon. If I calculate angular error I will need all legs of the polygon. If I calculate vertical error I will need all legs of the polygon. Why would linear error be any different - unless the report does not take into account linear error. I was taken aback by this because of all of the software packages I have used this was the first one that does not include the BS or tie in distance in the calculation of closure. :? Thanks for your input Richard and Glen.
Ted Moretz
 

Open Traverse

Postby Glen Cameron » Mon Nov 15, 2004 7:04 am

Maybe what you are looking for is not what we call a closed traverse. Maybe it is better defined as an open traverse. If I use the exact same traverse from above, and do the closure as if it were an open traverse, I get the following:

Starting Pt:194 Ending Pt:198 Type O

Starting BS bearing: N01°19'17"W Ending FS Bearing: S01°19'17"E
From Pt Angle Distance To Pt
194 91°19'17" 100.000 195
195 90°00'00" 100.000 196
196 90°00'00" 100.000 197
197 90°20'38" 99.682 198

Closure Report:
Current Closing Point vs True Closing Coordinates:
Current Closing North: -62.845
Current Closing East : 933.013
Actual Closing North : -63.165
Actual Closing East : 933.611
Distance Error : 0.678

Closure Ratio 1: 589
Total Traverse Length: 399.682
Closure Direction : S61°51'22"E

Our definition of a Closed Traverse is not the same as everyone elses so an Open Traverse may better match what you are looking for in a report and how it is generated.

Cheers,
Glen W. Cameron, C.E.T.
City of North Bay, Ontario
Glen Cameron
 
Posts: 1395
Joined: Fri Nov 08, 2002 12:18 pm
Location: Corbeil, Ontario, Canada

Postby Darcy Detlor » Sun Nov 21, 2004 11:29 am

I think that we are concerned about wording, when all we need to is provide a solution to the problem. Our definition of a "Closed Loop Traverse" is designed for a special case. Our "Open" traverse actually "closes" to a known point with an option of a closing foresight angle. This allows you to adjust angles. It is a still a "closed" traverse.

Our definition of "Closed Loop" traverse was originally created to simplify data entry. It is no different from our "Open" Traverse except there is no need to enter in some extra information because we know that the starting backsight point is the last point where you set up the instrument. It means no more than that. When you choose our "Closed Loop" traverse we define the starting backsight point and the original setup (POB) point as fixed and immovable points. You are actually closing on the BS point. Therefore the leg between the two is not part of the loop. The first angle from the backsight to the second setup is used for the angular calculations, and the last foresight shot angle (back to the POB) is used to compute the angular calculation, but the leg between the two is not part of the traverse, because the points are fixed relative to each other. The closure computation is the distance traversed from the first setup point to the point where the error is measured, which in this case is the distance between the last setup coordinate and the starting BS coordinate, divided by that distance error.

If you use the "Open" option, which is "open" only in the respect that you have to enter in a little bit more information, you will get the results you want, but the leg between the starting backsight point and the initial setup (POB) will be adjusted, and the starting backsight point will move.

I believe we could discuss the wording for quite a while, and it is possible that we would change the terms slightly, but in reality we offer several scenarios in our documentation which cover just about every possibility. As Glen stated, I think that you want to use the "Open" method to compute the results the way you want them.
Darcy Detlor,
President,
MicroSurvey Software Inc.
[email protected]
User avatar
Darcy Detlor
Site Admin
 
Posts: 205
Joined: Tue Oct 29, 2002 10:14 am
Location: West Kelowna, BC

traverse closure/type

Postby cadrum » Mon Nov 22, 2004 3:11 pm

I too had questions about this, but using FieldGenius. Thanks for the clarification.
cadrum
 
Posts: 21
Joined: Tue Sep 30, 2003 6:35 pm
Location: Florida, USA

Postby Dennis Trill » Tue Nov 23, 2004 12:19 pm

Darcy, I have found that by using the "Open" option to balance a "Closed" traverse, your program seems to throw an extra angle in the "Balance Angle" routine. In other words, I think most surveyors working outside of an integrated survey area would rather balance the traverse and then in a separate step, orient the traverse. Perhaps other users could voice an opinion on this.
Dennis Trill
 


Return to MicroSurvey CAD

Who is online

Users browsing this forum: Bing [Bot] and 1 guest

cron