Position each point in the recommended order below. Each adjustment helps straighten a larger section of the chart by moving entire grid lines, so fewer corrections should be needed later.

This guide continues from Straighten Chart. Before placing any points, make sure the corners and row and column counts are correct, then align the thick overlay lines with the chart's thick printed lines.

Work from broad corrections to local ones. Adjust the outer edges first, then the centre lines, and finish by checking each quadrant. This usually reduces the number of points you need to move.

1. Straighten the Outer Edges

Top and Bottom Edges

Move from left to right across the top edge, then repeat across the bottom edge.

Aligning points along the top and bottom helps straighten the chart's vertical grid lines across its full height.

Left and Right Edges

Move from top to bottom along the left edge, then repeat along the right edge.

Aligning points along the left and right helps straighten the chart's horizontal grid lines across its full width. Going from top to bottom helps keep the magnifier out of the way.

2. Correct the Centre Lines

Work Through the Middle

Work across the horizontal centre, then down the vertical centre.

These two passes correct distortion through the middle of the page and divide the remaining work into four smaller areas.

3. Refine Each Quadrant

Finish the Remaining Problem Areas

Check each quadrant, tap and align all points in that area.

Most of the points should already be pretty close and only minor adjustments required. Work through the four quadrant in any order,and just ensure the grid points nicely align with the underlying chart.

4. Fine-Tune with the Magnifier

Tap a blue point to select it. The selected point change colour and the magnifier shows the printed intersection in detail. 

A selected straightening point shown in the magnifier

Drag the point on chart, or drag you finger within the magnifier, to get close. Then use the four arrows inside the magnifier to finely adjust the point location. Single taps on an arrow nudges the point by one pixel; double-tap nudge moves it faster.

5. Use x5 for Difficult Bends

In x5 mode, the additional blue points sit halfway between the main x10 points. Use these only where the printed grid still bends away from the overlay after the broader corrections. This is for finer control over chart image adjustments. 

For a sharp local bend: Switch to the x5 layout for more control, then add points only around the affected area. Recheck the thick-line alignment before continuing because changing the spacing or offsets resets placed points.

The x5 layout showing additional straightening points between the main ten-square intervals

 

6. Apply and Review

Once all the points on the grid are aligned with the underlying chart, tap on Apply. Markup will use its magic and attempt to straighten the chart image using the pre-positioned points. Review the output by zooming in and check that the grid lines align nicely with the chart image. If not, you can repeat the process and add more points, or alternatively, click Undo in the toolbar and adjust the position of the original points. 

  1. Tap Apply to straighten the image using the points you placed.
  2. Inspect the entire grid, not only the area you adjusted, zoom in and pan around.
  3. If necessary, add or move a few points in the remaining problem areas and choose Apply again.
  4. Use Undo and Redo to compare applied versions before you finish.

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