1 · The shapefile

Drop the set together — .shp with its .dbf, .prj, .shx (and .cpg) — or one .zip of them. Nothing leaves this browser.

Drop the shapefile files here

or

2 · From which coordinate system to which

Source (what the numbers are now)

Target (what you want)

Ordnance Survey model (position and height)

Used whenever British National Grid or a site grid is on either side: OSTN for the position, OSGM for Newlyn-datum heights. Both are our own implementation of the published OS method, checked against OS's test points to the millimetre.

Heights

From the shape's Z, from a numeric attribute column, or none (2D drawing).

Units in

Units out

3 · The site grid

A site grid here is British National Grid with the scale factor removed about an origin and a shift in E and N; heights stay as they are unless you add an offset. Type the parameters, or solve the shift from common points.

Origin E

Origin N

Scale factor to remove (k)

Site coordinates = origin + (grid − origin) ÷ k. Leave blank to keep grid scale.

Height for the height factor (m, Newlyn)

Rotation (degrees, anticlockwise)

Shift ΔE

Shift ΔN

Height offset ΔH

Solve the shift from common points

One point per line: grid E, grid N, site E, site N (commas or spaces). The shift is solved about the origin above; tick rotation or scale to solve those too.

rotation scale

4 · The drawing

Label points with

Layer from

Layer name (when not from a column)

Text height (drawing units)

Decimal places

Then open the DXF in AutoCAD and save as DWG, or run it through the free ODA File Converter.

Try one point first