Using 2 or more points for backsight

Moderator: Carlson Support

Using 2 or more points for backsight

Postby tony45power » Fri Sep 11, 2009 1:34 am

I am working on a big foundation job and everyday day they keep moving mounds of dirt on me always in my view!

I resection new points to work with everyday and i am using prisms mounted on the surrounding buildings in the area. Well everything is good but when its gets really hot the prisms shift on me and also its hard to take a good line onto a prism depending on the angle.


My problem is when i setup onto a knowing point and i need to stake out a line i can only take a back sight onto 1 prism (back sight) If that prism shifts say a 1/4" my angle is off a 1/4" for all my shots. I would like to before staking out a line take a back sight to 2 or 3 known back sights (or prisms) and adjust the error between all 3. Is this possible?
If i resection a point then my back sight is already adjusted for!! I dont want to resection new points though everyday i would like to work consistent with the same occupy point and adjust my back sights.
tony45power
 
Posts: 13
Joined: Sun May 24, 2009 7:23 pm
Location: nyc

Postby ColC » Tue Sep 15, 2009 11:21 am

I think your problem is one which may be beyond the expectation of technology but within the scope of good surveying judgment. I know that feeling of having the greatest plans of mice and men ruined by a lump of fill or pile of material on the line of your targets.

Your idea of taking a mean of the readings sounds found. I would be reticent to undertake a resection on a known or fixed point when the conditions to your control are not ideal. Remember if your backsight is sufficiently distant from your area of operation then the 1/4" is reduced in proportion to the distance of the backsight and the distance to your setout point. Whereas, if you do a resection and create a new point, the difference is directly transferred to your setout points.

If you are happy with your control and the precision of each of is uniform then a resection is a good option. If however, you wish to weight some points as being more stable and tighter then you might have to just make a set of comparisons of your measurements on the day against the control measurements and make the adjustments with some weighting based on your judgement.

Good luck with it all
ColC
 
Posts: 204
Joined: Mon Oct 29, 2007 9:35 am
Location: Toronto,NSW Australia

Postby ColC » Sun Sep 27, 2009 12:14 pm

I just viewed the recent webinar on the 2010 release. There is a nice new option for multiple backsights which is mentioned as being available in the 2.5 release. This may help give you yet another aid to solve those difficult field situations.
ColC
 
Posts: 204
Joined: Mon Oct 29, 2007 9:35 am
Location: Toronto,NSW Australia


Return to SurvCE General

Who is online

Users browsing this forum: No registered users