super accuracy positioning, precise levelling

[carlorom]

To measure top of a circular concrete pier 2m wide (inner diameter about 13m) about 1.5m up from datum point within 0.2mm on a grid of 150mm spacing (this will mean around 3000 points)

To test same for flatness deviation all round not to be more than +-0.5mm

To establish whether this "ring" is within 0.1 degree of horizontal.

This is then also connected to establish position to a nearby tower to within 0.5mm (distance around 30m further but much higher (I guess around 30m up)

Any suggestions as to methodology, precautions to be taken, and suggested instrumentation will be welcome. A bit of brainstorming on this would be welcome.

I propose to use a precise electronic level to get the levels to 0.2mm. What worries me is the positioning of the points on the pier (3000 of them) in plan (Y-X) to this same degree of accuracy or even 0.5mm. To this effect I envisage two single second total stations on a baseline within 1mm accuracy (EDM specs are 1mm plus 2ppm). The simultaneous intersection using such instruments (duly calibrated) should yield accuracies of this order as long as the baseline is around twice the diameter of ring.

I believe the site is also quite windy sometimes!

Any advice is welcome!

 

[allanhosking]

Hi,

I am a Kiwi surveyor with 11 years experience currently working in Singapore.

I suggest you contact Otago University in New Zealand who have in the past had to resolve such precise survey problems in their industrial engineering department which specialises in such high accuracy projects.

For a simple low cost solution your approach seems OK.

I have recently started using a 3D laser scanner from a company in france called mensi at

http://www.mensi.com.

They have 3D laser scanners that can measure to within 0.5 of a millimeter 100 points per second with their short range version. Although each measurement is slightly out of spec because you measure thousands of points in minutes the surface 3D model generated to far more accurate. No good for setting out but ideal for high accuracy as-built. We have one in singapore at

http://www.hydronav.com.

Good luck

Allan Hosking
allanhosking@hotmail.com