Straighten Chart can help straighten bowed, curved or wavy grid lines e,g,, when a chart has been photographed from a book. It reshapes the underlying chart image so the printed grid better aligns with the Markup grid and can be stitched accurately.
This is an optional step after Confirm Size. Use it when the corners and grid size are correct but the printed lines still curve away from the overlay. Any saved changes here will update the original PDF file.
Before you begin: The grid corners and row and column counts must be correct before entering this step. If even one row or column is missing, straightening cannot produce an accurate result. Also, ensure to align the thick overlay lines with the chart's thick printed lines before placing any points; changing the spacing or offsets later resets the points.
This reminder appears before you begin. Make the offset adjustments using the toolbar icons at this point, before investing time in individual straightening points.
Straighten Chart at a Glance
The chart is shown with a red grid overlay and straightening points. The toolbar controls the grid spacing and offsets; Apply previews your correction, and Finish saves it.
The Basic Workflow |
1. Check your inputs!
Confirm that the outline follows the chart boundary and that you have the correct row and column counts for that page. Go back to Confirm Size to fix this first if anything is wrong. |
2. Align the thick grid lines
Use the left/down offset arrows in the toolbat to ensure the thick grid lines match the chart's thick printed lines. Do this before placing points. This makes it easier to align the points when zoomed in with the magnifier glass. |
3. Tap and move grid points to align with chart image
Tap the grid intersection points to open the magnifier and move each selected point onto the corresponding intersection on the underlying chart image. Use the arrows on the magnifier for precise placement. |
4. Apply and review
Tap Apply to straighten the image, then inspect the result. Use the Undo icon in the toolbar to go back to point slection after applying. Add more control points and re-apply to see the results. |
5. Finish
When the grid and chart image are aligned across the page, choose Finish. Markup saves the adjusted grid and, after confirmation, updates that page image in the project's source PDF. |
The Toolbar
Set Up and Review the Grid |
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- Undo and Redo: Step backwards or forwards through updated chart image after tapping the apply button.
- Point spacing: Switch between x10 and x5. Use x10 for broad corrections and x5 when a smaller grid area needs finer control to straighten up.
- X offset: Move the pattern of thick vertical overlay lines sideways until it matches the chart.
- Y offset: Move the pattern of thick horizontal overlay lines up or down until it matches the chart.
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Learn the Process
Detailed Guides |
- Point Selection Order : follow the suggested order to update/move the points on the chart. This will hopefully help to achieve consistent results.
- Precise Point Placement : drag and moves each pooint to first get is somewhere close to the underlying chart position, then use the magnifier to finely adjust.
- More Points for More Control : switching from x10 to x5 increases the number of points to align on the chart but give you more control around local distortions.
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Important to Know
- Initial correct setup matters more than the number of points. Wrong corners or counts cannot be fixed by adding more straightening points.
- Start broad, then refine. Align the main edges and centre lines before working on individual corners or local bends.
- Use x5 only where you need more control. The denser layout is useful around sharp bends, folds and difficult corners.
- Apply can be repeated. Review each result, add or adjust points, and apply again until the overlay follows the printed grid.
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