Digitizing points: series, snap, undo

6. Series and point acquisition

Creating a series

Open the Series tab and press New. Each series contains:

Series name
Parameter name
Parameter value
Parameter unit

Series name and parameter name are required. Parameter value and unit may be empty, but consistent values are strongly recommended for later scientific export.

6BX7-GT example

Series name: Vg_-20V
Parameter name: Vg
Parameter value: -20
Parameter unit: V

Active series

The table displays Series, Parameter, Value, Unit, Vis and Pts. Clicking a row makes that series active. New points are always added to the active series.

Add points mode

Select Add points and click along the curve. For each click the program:

1. records the manual click;
2. optionally applies local snap;
3. stores the effective pixel;
4. calculates X and Y when calibration is available;
5. adds the point to the active series.

Points are displayed as colored markers. The selected point is drawn slightly larger and thicker.

No interpolation

The program does not draw an interpolated line between samples and does not add automatic points. This keeps explicitly acquired data visually distinct from derived data.

Point density

For later nonlinear fitting, use more points where the characteristic changes rapidly and fewer in nearly linear regions, while avoiding manual smoothing. Digitization should represent information actually visible in the graph.

Progressive numbering

Show progressive point numbers displays 1, 2, 3… beside the markers. Numbering restarts for each series and affects display only.

Editing series metadata

Select a series and press Edit to change its name, parameter, value or unit. Existing points remain attached to the series.

Show and hide

Show / Hide controls only Canvas visibility. Hidden series retain their data and are still included in CSV export.

Deleting a series

Delete removes the selected series and all of its points after confirmation. The operation can be recovered with Undo while it remains in history.

Parameter consistency

CSV export uses one parameter column for all series. A project intended for one combined CSV should therefore use consistent parameter semantics and units across its series, for example all Vg values in volts. The application performs no automatic unit conversion.

7. Point correction, snap, undo and redo

Edit / move points

Select the appropriate series and enable Edit / move points. Click near a marker and drag it to a corrected position.

The selection routine searches for the nearest point within about 10 screen pixels, keeping point selection practical across different zoom levels.

Selected-point information

The side panel displays:

• Manual click coordinates;
• Stored pixel coordinates;
• calibrated X and Y, when available.

Deleting a point

Select a point in edit mode and press Delete, or use Edit → Delete selected point.

Optional local snap

Snap to darkest local pixel finds the darkest pixel inside a square centered on the manual click. The radius is expressed in source-image pixels and can be configured from 0 to 25 in the GUI.

If several pixels share the minimum grayscale value, the candidate nearest the manual click is selected.

Why snap requires caution

Datasheet grids can be as dark as, or darker than, the plotted curve. A large snap radius can therefore move a point onto a grid line instead of the desired characteristic. For this reason:

• snap can be disabled at any time;
• small radii are preferable;
• the original manual click is always preserved;
• snapped points should be visually reviewed.

Practical strategy

Start with snap disabled. If the curve is dark, continuous and well separated from the grid, try a radius of 1–3 image pixels. Disable snap if markers are attracted to grid lines, axes or text.

Undo and redo

Ctrl+Z  Undo
Ctrl+Y  Redo

The application keeps project-data snapshots, with the standard history trimmed to roughly 100 states. Point additions/removals, point moves, series edits, calibration changes, visibility and display/snap settings are among the operations that use this mechanism.

What undo does not restore

Canvas zoom and pan are view state, not project state, and are not restored by Undo/Redo.

Recalibration without redigitizing

If calibration points or axis limits are corrected later, all calibrated coordinates are recomputed from the stored pixel positions. The curves therefore do not need to be digitized again solely because calibration was improved.