iPhone · Local projects

LineLatch support

Calibrate an image from a known reference length, keep its settings, and export a tiled PDF for printing.

Make your first print project

Import your own JPG, PNG, or HEIC image from Photos or Files, or open the included Practice template.
Place point A and point B on the ends of a reference line. Enter the line’s actual length in millimeters or inches. Use zoom, the loupe, and point controls to refine the selection.
Choose A4 or US Letter, orientation, margins, and overlap. The entire image, including any white border, is the output area.
Export the calibration sheet first. Print at 100% / Actual Size, turn off Fit to Page, and measure the ruler before cutting your material.
Preview and export the tiled PDF. Use the page labels and assembly guides to arrange the sheets.

Check the source and the printer

Use a flat, undistorted image and a reference length you trust. LineLatch calculates PDF dimensions from your selected points. It does not correct camera perspective or control your printer. A correct PDF can still print at the wrong size if the print dialog rescales it.

Measure the calibration sheet on paper before relying on a print. Digital checks do not replace that measurement.

Keep an editable backup

Your saved project keeps the image received from the system picker, reference points, length, unit, and paper settings locally. A PDF is printable output; it is not an editable project backup.

Use the project’s backup action to export a .scaletrace file to a location you trust. Restore that file to create a new project. A supported restore does not replace your current library. If a backup cannot be read, keep your existing projects and choose another backup.

A backup includes the imported image and any metadata retained in it. Review where you save or share it. Back up important work before deleting the app, changing phones, or deleting a project; LineLatch has no developer cloud account or automatic cross-device sync.

Files and limits

One single-image JPG, PNG, or HEIC/HEIF file: at most 10 MiB (10,485,760 bytes) and 24,000,000 pixels.
Full-image output: at most 1000 mm on either side. Layouts beyond the 64-page safety limit are refused; other size limits can produce a lower maximum.
Margins: 5–25 mm. Page overlap: 0–20 mm.
Editable backup input: at most 12 MiB, using the supported LineLatch backup format.

Source PDF/SVG import, image cropping, perspective correction, and direct printer control are outside this version. Use images you created or have permission to use.

Delete a project and manage copies

Deleting a library project removes its saved project, source image, and temporary export copies managed by LineLatch. Files already saved or shared to another location remain there. Delete those separate copies in Files, cloud storage, or the destination app if needed.

If saving or exporting fails, keep the project, check available device storage, and retry. Do not delete the app to troubleshoot without first saving an editable backup.

Purchases

LineLatch uses a one-time App Store download price. This version has no in-app purchases, subscription, or separate feature unlock. Apple handles download purchases and refunds through your Apple Account. Re-downloading the app does not restore a local project library; keep editable backups.

Contact

Email wzq12200609@gmail.com for LineLatch support.

Include the app version, iPhone/iOS version, selected paper, margins and overlap, and what happened. Avoid attaching private images or backups unless you deliberately choose to share them for troubleshooting. The app does not automatically send diagnostics or attachments.

Publisher: Jason Wu · App Store seller: 志强武.