Loop Closures

[Peter Smart]

Hi,


 Can someone give me alink to somewhere that survey loop closures as in Survex are carried out anddocumented? 



Im OK with the general principle but don’t really understandthe stats and listing in Survex. I understand that the loop is broken down to anout and back lines defined by nodes which link to other points in the survey.BUT:


1)  Is it moved a horizontal or sloping distance iedoes it take account of both plan and elevation loop closure? How much of theerror is then vertical versus horizontal?
2)  There are 3 numbers listed after the originallength distance moved etc line in the output. The first is on a line alone with no designation the other two arelisted as H: nnn and V: nnn. Is this information about the vertical and planmissclosureverall?  is the loop closure routine progressivestarting from small and working up to large loops or is it an errorminimisatiion optimisation type scheme?
4)     Some of the legs involved in a loop end up withzero movement despite the tie line moving substantially. This gives zero errorson the out part of the loop and significant ones on the return section. Is thissimply a matter of geometry eg the error may be in easting only so legs thathave only a northing component aren’t corrected?
Survex is capable of including different standard deviationsfor individual survey lines or legs. Does the loop closure routine take thisinto account eg by forcing more movement on a BCA grade 3 line compared to BCRAGrade 5? Issue is if you have a reliable survey how do you force this to havemore say in the final positions after loop closure compared to the lower gradesurvey without simply fixing a point at the end of the ‘good’ survey?
Thanks for that Pete S

 

Peter Smart
nzoia1 at aol.com