Hi, Am 11.01.2018 um 10:54 schrieb Tom Hughes: > Looks like we are using 90dpi actually. The key code is here: > > https://github.com/openstreetmap/chef/blob/master/cookbooks/tile/templates/default/export.erb#L121 > > > We project the bounding box from EPSG:4326 lat/lon to spherical mercator > which gives us coordinates on a projected sheet measuring roughly > 40075016m on each edge (2 x PI x assumed earth radius). > > We then divide by the scale factor and then convert metres to pixels by > dividing by 0.00028 which comes from: > > 1 / 39.701 / 90 > > Where we divide by 39.701 to convert from metres to inches and then by a > further 90 to convert to pixels at 90 dpi.
Nik4 goes one step beyond and multiplies the scale by (1 / cos(lat)). lat is the latitude of the centre of the rendered image. That's a pretty good approximation. https://github.com/Zverik/Nik4/blob/master/nik4.py#L289 Best regards Michael -- Per E-Mail kommuniziere ich bevorzugt GPG-verschlüsselt. (Mailinglisten ausgenommen) I prefer GPG encryption of emails. (does not apply on mailing lists)
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