15 Jun 09 12:56
For a large project, such as a hydroelectric development, the construction drawing will contain a project layout and control drawings, in which dimensions will be provided in true lengths, rather than in a UTM coordinates, such as NAD 83 coordinate system.
Since the topo maps are established from a UTM coordinates, a scale factor will be used so that the survey measurements (in true length) can be represented correctly in the field.
The scale factor can be calculated, based on two items: (1) location, and (2) elevation.
The location will determine the horizontal scale factor, and the elevation will give an elevation scale factor. Both will be combined to come up with a combined scale factor.
For simplicity, it would be nice to pick up a scale factor (usually to the fifth decimal, such as 0.99922) for the whole project site. This would be a combined scale factor utilizing the location and elevation.
My question is as follows:
Assuming a project site about 2-3 square miles. We can assume that the coordinates within this area will generate a single horizontal scale factor, relatively unchanged to the fifth decimal.
How do you deal with the elevation? Should you use an average elevation, pick up max and min and average them, or by other means? This is assuming that elevation within the project site will not allow to pick up a single elevation scale factor to the nearest fifth decimal.
Just for (1) and (2), is the common guidelines just to pick up an agreed combined scale factor?
I would like to have a discussion or comments please