On Jan 6, 4:56 pm, Bill Chadwick <[email protected]> wrote: > Hi Bratliff. > > The UK OS Projection is like one wide UTM zone. Both UTM and UK OS are > Transverse Mercator though with slightly different parameter values. > There is no reason why the same techniques can not be used to reproject > similar scale UTM tiles onto Google tiles. You could no doubt re-project UTM > tiles from more than one 6 degree UTM zone on to one Google map, provided > you know which zone the source tile is on. Of course, the technique relies > on the source and transformed tiles being of similar scales (meters per > pixel).
TerraServer, which Microsoft has pretty much abandoned, provides a few tiles of overlap at zone boundaries but not much. Horizontal panning at a zone boundary is chaotic. The Eastern tiles in one zome are different than Western tiles in another zone for the same location. Fortunately, UTM is not very popular in the US except in the military. > As you say, the advantage of re-projecting tiles is that we can use the > Google API to draw markers, polys, routes, heat maps ... Of course any grid > lines on the reprojected tiles end up not being screen north aligned and > there is a degradation in text/symbol rendering quality with interpolation. I suspect you have to use pieces of four UTM tiles to build each Mercator tile. > This is what lead me to try a custom projection for the UK tiles. Sadly > though we can draw markers on a custom projection map we can't do anything > with polys (and so I assume routes). Google have not responded in any way > (PM or forum) about vector rendering being broke for non Google projections. > I have posted the issue as a bug - star it if you like. I saw it but I did not star it because I quit using TerraServer a long time ago. > I expect that the performance of per tile affine transformations (whether > source tile or target tile) will probably outperform any per pixel or small > pixel group translations. Its possible that CANVAS may be a better solution > than SVG for the non IE browsers - I've not played with it that much yet. If > someone wants to port what I have done in SVG to CANVAS for a performance > comparison then that is fine by me. Just another approach to consider. I suspect it could be used to transform EPSG 4326 to Google's Mercator projection because just the vertical component is involved. A CANVAS element can be moved quite quickly during dragging / panning / zooming. If the browser has to rescale tiles, performance is degraded. > Per pixel (or pixel group) will of course be the only way for tiles that > cover a large portion of the earth - try zooming my OS demos right out and > you will see that things eventually degrade. > > The solutions I have presented should be good for IE >= 6 , and the in use > versions of the other main stream browsers. I don't believe that CANVAS is > supported in IE until the new MSIE9. -- You received this message because you are subscribed to the Google Groups "Google Maps JavaScript API v3" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/google-maps-js-api-v3?hl=en.
