Quiet Pleasures of Geo-Rectification
I finally gave the new OpenLayers Map Rectifier a serious crash test today, and a few hours later I was still in the same quiet groove, with rosy visions of what it might make possible for historical geography. The rectifier has enormous potential to give users an easy point-and-click interface for geo-referencing and then warping their own flat maps of places, for use as layers in a geographic database. What this means is that I now am within reach of a tool which will allow me to begin creating layers of the various maps of Bombay and loading them as layers in the Mumbai Free Map, as I can now easily warp any image by making a few markers based on common landmarks between the source map and reference map.
This screenshot shows the 1969 Bombay City Guide Map loaded into the rectifier, tagged with a few common markers between the source image on the left and the new layer on the right, now warped according to the surface of the earth. Chris Schmidt helped squash a small bug to get this rendering to work, and I’m hoping that the team can implement the projection system for Mumbai (WGS Datum 84 and UTM Zone 43N) so we can begin serving layers live to the Mumbai Free Map. In anticipation, I uploaded high-resolution maps of Bombay, Salsette, and parts of Thana and Colaba from 1926, 1930, 1933, and 1969. Go to to one of these maps and zoom in on a neighbourhood you know, and load up the satellite imagery in the reference map, and click away.
