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Two Coordinate Systems in One Project. Advice Needed.

Question asked by Marshall Cant on Aug 10, 2020
Latest reply on Aug 20, 2020 by Marshall Cant

Greetings: If this is not the place to ask this question then please redirect.

We are about to start a small 'run-of-river' hydroelectric project. I received the first drawings yesterday and noted immediately that the project is designed in two coordinate systems: UTM and a local made up system.

The UTM covers the ROW clearing, earthworks along the penstock, site roads etc. The Intake structures and the Powerhouse are designed in the local system. The total length is approximately 2km overland between the Intake, along the penstock, and down to the powerhouse.

It appears that the two systems only overlap at the limits of each section. The control I was provided with by the engineer is clustered in two groups, one at each end: a cluster at the Intake end, and a cluster at the Powerhouse end. Nothing along the penstock alignment.

Transformation parameters have been provided between UTM and Local but tests I have done converting one to the other and back are showing small residuals (+/- 5mm).

My plan is to calibrate the site as if it was two "projects". One would be the Site UTM and the other the Site Local. I would create and maintain the Intake and Powerhouse in TBC as one project, and the Penstock as another. This would keep quantities, grade control, and layout files separate and not require the field surveyor to bounce between the two systems. I would transform only coordinates that are in the "overlap" zone between each part (ie Intake To Penstock, and Penstock to Powerhouse).


My Question: does this make sense to do it this way? I want things to be as foolproof as possible. Is there any issue with control being clustered at each end?


Any other ideas would be greatly appreciated.

Many thanks in advance.