Digitising overview#

Digitising is the stage where GraphX turns calibrated positions on the source image into a usable dataset. Calibration defines how an image location maps to graph X and Y values; digitising records the locations you choose and calculates their coordinates from that mapping. A valid calibration is therefore required before GraphX can add calibrated points.

Every point belongs to a dataset. The active dataset is the destination for manual points and accepted traces, and is the dataset shown in Data points. A graph containing several plotted series is normally easier to manage when each series has its own dataset, colour, point order, and export choice. See Datasets for the organisation controls.

A practical digitising workflow#

1. Select or create the destination dataset.
2. Choose Add/edit points for manual placement, or Trace curve for a visually distinguishable line.
3. Collect points and inspect their values in Data points.
4. Correct, select, sort, or delete points as needed.
5. Choose dataset Precision for the way values should be displayed and exported.
6. Optionally continue to a trendline, then export results or save the project.

The source-image position remains useful after placement: if calibration is adjusted later, GraphX can recalculate a point’s graph coordinates from that location. This makes it worth checking both the point marker and the resulting values before moving on.

Manual point placement#

Use Add/edit points for sparse data, selected samples, and any situation where you want direct control over each source position. It is also the way to correct points created manually or by tracing. The lower-left coordinate overlay shows the current source-image and graph coordinates while you work. Adding and editing points covers placement, direct coordinate entry, selection, deletion, and history in detail.

Curve tracing#

Use Trace curve when a plotted line is visually distinguishable from the grid, background, and nearby series. You click a seed on the intended curve, inspect a preview, choose the required output count, then accept it into the active dataset. Curve tracing is colour-guided image analysis rather than semantic graph recognition, so it should be reviewed before acceptance. See Curve tracing.

Working accurately#

Axis lock fixes one calibrated coordinate while you choose the other. It is useful for values sampled at prescribed X positions, repeated Y levels, or a sequence taken from another dataset. It follows the calibrated graph geometry even when the image is rotated, sheared, or photographed. See Axis lock.

The Precision magnifier is a visual placement aid in the toolbar’s Display menu. It enlarges the original image around the cursor. Dataset Precision is different: it controls the numerical formatting used in Data points and supported exports, without reducing stored coordinate accuracy. See Precision.

Review and recover#

Points outside the calibrated X or Y range are marked as extrapolated because GraphX can calculate them, but the result depends on extending the calibration beyond its references. Data points provides selection, cleanup, sorting, and Undo/Redo controls. Undo and Redo cover the normal point-changing actions, so it is safe to correct a point or accept a trace and then review the result.