Philip Ryan via QGIS-User <qgis-user@lists.osgeo.org> writes: > Hello, > I am trying to digitise a series of old gold lease "portion plans" > produced in the 1880s in Australia by a mining surveyor using a > compass and chain. The data for each gold lease includes a table of 1) > compass bearings in degrees and 2) distance measurements in links (0.2 > m) for each vertex of the lease polygon (mostly a rectangle or > trapezoid but sometimes more complex).
>From a US perspective, a link being 0.2 m is interesting. Here we have a 66 foot chain with 100 links. That turns out to be 201mm, something I had never realized. I wonder if your data is in Gunter's chains, or in some metricified version where a link is really 0.2m. Sort of like how the kids in Europe drag race in "metric quarter miles" of 400m, or so we imagine in the US. https://en.wikipedia.org/wiki/Gunter%27s_chain What you are trying to do (abstracting "gold lease" to "survey plan without global coordinates) seems common, and I have not really understood the best way to proceed. I think there are two parts: Capturing the survey plan in a local coordinate system *for that plan* which is going to be in distances at ground level (vs reduced to the ellipsoid) and oriented to perceived local magnetic north as of the date of survey (or for more modern plans, adopting a basis of bearings of some previous regional plan). Transforming that local coordinate system to global coordinates. This is a scale factor, perhaps left at 1 if there's no real evidence otherwise, translation and orientation. For the second part, it would be great to have a tool that lets you match up both coordinates and stores them in a control file you can edit, and produces an object you can use with proj. The georeferencer almost does this, but apparently only for images, and it's a little unclear to me about storage and redoing. _______________________________________________ QGIS-User mailing list QGIS-User@lists.osgeo.org List info: https://lists.osgeo.org/mailman/listinfo/qgis-user Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user
