Tool 10 · PDF underlay

A PDF plan becomes
a drawing with real coordinates.

Import a cadastral plan or a CAD sheet as PDF, tie it to two or three points you know, and trace points, lines and polygons over it. The PDF is processed on the phone, with no upload.

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4 steps
3 fit methods
5 export formats
GeoKantar: a georeferenced PDF plan over satellite imagery with a traced polygon
Tool

What the tool does

Four steps along the top of the screen: Import, Georeference, Draw, Export.

InputA PDF up to 30 MB, any page. Vector PDFs from CAD and scanned drawings both work
CropSelect only the part of a large sheet (A1, A0) you need, so the drawing stays sharp
Transparent paperWhite becomes transparent, so satellite imagery shows under the lines
SnapThe crosshair locks onto vertices of a vector drawing, or onto corners detected on a scan
Fit methodsHelmert (2+ points), affine (3+ points), or one point plus the drawing scale
Quality checkRMS, a residual per point, pixel size on the ground, drawing scale and rotation from north
DrawingPoints, lines and polygons with live length, area, perimeter and segment azimuth
ExportDXF, CSV, GeoJSON, KML, or the georeferenced image with a world file
Procedure

How to use it

01

Import the sheet

Choose the coordinate system your control points are in, then the PDF and the page. Turn on cropping for a large sheet.

02

Add control points

Bring the crosshair to a point whose coordinates you know, add it and enter E and N. You can also take coordinates from saved points or pick a place on the map.

03

Check the fit

With three or more points every point gets a residual and the fit gets an RMS. The app warns when points are too close together or nearly on one line.

04

Draw and export

Trace over the drawing with snap, name the objects, then export them, or save a polygon as a parcel for the Area and Subdivision tools.

Details

Things worth knowing

Helmert, affine or scale

Helmert keeps the shape of the drawing: shift, rotation and one scale. Affine allows a different scale across and down, which suits scans on shrunken paper. Scale needs one point and the drawing scale, and assumes north is at the top of the sheet.

Accuracy comes from the control points

The drawing can never be more accurate than its control points. Use measured boundary or survey points; a place picked on satellite imagery is only good for rough positioning.

The image goes to CAD too

The ZIP export holds the georeferenced image with the ATTACH values and a DXF for AutoCAD, and a world file that Civil 3D and QGIS read on their own.

Drawings are kept

Every imported sheet stays in Saved drawings with its control points and objects, so you can reopen it and keep drawing.

Questions

Frequently asked questions

Does the PDF leave my phone?

No. The page is rendered and the snap points are found on the device. Only the satellite basemap in the Draw step needs a connection.

How many control points do I need?

Two for Helmert, three for affine, and one if you know the drawing scale. With three or more you also get a residual for each point and the overall RMS.

Does it work with scanned plans?

Yes. On a scan the app detects corners in the image and snaps to those. A vector PDF from CAD gives the most accurate snap because it uses the real vertices of the drawing.

What can I export?

Drawn objects go to DXF, CSV, GeoJSON or KML. The sheet itself can be exported as a georeferenced image in a ZIP, for AutoCAD, Civil 3D and QGIS.

Get GeoKantar

This tool ships inside the GeoKantar app. Available on the App Store and Google Play.

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