On Tue, 2010-03-30 at 16:21 +1300, Stephen Irons wrote: > On Tue, 2010-03-30 at 12:09 +1300, Craig Falconer wrote: > > Roy Britten wrote, On 30/03/10 10:50: > > > Created with Image Magick from a number of TIFFs obtained from the > > > LINZ web site (where all the new 1:50,000 series maps are available > > > for download). I have to stitch together 6 maps to cover the tramp I'm > > > doing later this year. > >
snip Maybe it is time to update my browser-based map viewer. I inherited an original CD containing the 260- and 262-series of topographic maps of South Island. Unfortunately, the viewer was Windows-based, and I wanted something that would run under Linux. The maps themselves are JPEG image tiles which the viewer pieces together in much the same way as Google Maps. I looked at GSIV (the giant-ass image viewer). This is lets you divide a big image up into tiles, then provides a browser-based Javascript viewer to piece them together. It worked, and I even managed to get it to print the coordinates in pixel position (on the screen, and on the map as a whole), as well as position in NZMG coordinates, which is just a linear scaling of the pixel position on the map. However, it was getting very unwieldy, and I wanted to get lat/lon position; the calculations were very difficult in Javascript. By this time, the OpenLayers project had progressed and become very useful. This is a general purpose browser-based map viewer. It can read map images from a number of places (Google maps, Yahoo, Microsoft, Open Street Map, etc), as well as used tile-based maps. I created a map layer that works with the 260- and 262-series map tiles from the CD. There was a bit of work in getting it to transform the coordinates from pixel position to NZMG and vice versa, but they have a standard way of naming and implementing this type of transform. The conversion to and from NZMG is now part of that project, so anyone can use it. And once the transform was implemented, then any of the standard coordinate systems become available. Great. However, it uses the old 260- and 262-series maps. The images are copyright of the people who created the CD. I do not have a problem using them for myself, but did not feel comfortable sharing them with friends, etc. But now LINZ has released the Topo50 and Topo250 series TIFFs with a gratis licence, I can share them with friends. The licence says 'You are welcome to reproduce LINZ maps at no cost...the following acknowledgement should be shown on the product and associated media...'. Not a free licence, but at least I can give them to friends. So, the project becomes: * Download the 31 Topo250 maps and the 451 Topo50 maps. The two I have donwloaded are about 50 MB (lots of plain blue sea) and 90 MB (lots of contour lines). Assuming an average of 90 MB, this gives a total of about 40 GB. Have to do this over a period of time... * Remove the borders, legends, etc. * Divide into tiles of a suitable size. Can the tiles be compressed to conserve space? How can it fit onto one DVD? * Create an OpenLayers layer that knows how to find a given tile for a position in a suitable coordinate system. * Viola. A cross-platform map viewer for Topo50 and Topo250 maps. I guess the way to download the original maps is to put in place a script that downloads a map, removes the borders and splits it into separate tiles. Then whenever I need a map of a particular area, download the one or two original maps needed, and create the tiles from it. Stephen Irons
