# Part 2: Reduction to the mapping plane

In class we also reviewed the concept of reducing a geodetic or ellipsoid distance to the mapping plane.

## Step 1: Implement the reduction

I would like you to create a C++ function or Google Spreadsheet that implements this correction for the distances measured in the first part of this lab. In other words, I want you to compute and apply the appropriate grid scale factors. Use the latitude and longitude of each point provided here.

Point

You are required to use the process outlined in this paper by Charles Karney ».

I’d encourage you to make much simple(r) work of this by looking at the code for the same thing found here ». Treat that code as guidance from which you can develop your own solution.

Use the parameters of the GRS80 ellipsoid for your calculations.

## Step 2: Check your implementation

Although you don’t need to hand anything in for this step, I would encourage you to check your implementation for at least one point using the online calculator found at the second link above.

## Step 3: Reduce the measured distances

Use your implementation to reduce the three measured distances that were provided in the first part of this lab. You may need to calculate a scale factor for the line(s). Provide:

1. The scale factor you applied in each case

2. The reduced distance

## Step 4: Prepare and submit a suitable summary of your input and output

If you used Google Sheets this might just mean the link to your spreadsheet. Be sure to share it so that it’s accessible to us as in previous labs.

In C++ this would mean submitting your input and output files.

## Step 5: Draw some conclusions

I’d like you to comment in your submission on the magnitude of the reductions being made here. How big are they? On what do they seem to depend? When would you recommend doing them?

## Step 6: Submit your work

When you’ve finished Parts 1 and 2 of the lab you need to submit them using the report template. There’s less to this lab than in previous labs, but be sure to use sensible headings and be sure to cover off what’s listed in the marking rubric. Also be sure to make it easy for us to find your Spreadsheet or input / output files. This was a straightforward lab about implementing some reductions. No need to overanalyze. Just show us what you did. Think about the report you write as helping us give you a good mark on the rubric.

If you don’t do Part 3 then you can submit your work and report individually.

If you decide to do Part 3 then you can come together as a team and submit a single report in the next section.

Welcome (back)!