[OpenLayers-Users] Saving with a Google Maps base layer

[Jan Martin]

Hi,

check out gpsdrive.
They have quite a lot on calculating and downloading tiles not just from
google.

http://apps.sourceforge.net/mediawiki/gpsdrive/index.php?title=Creating_maps
http://gtm.tel.uva.es/ztep/maps/dmap.htm

Jan


On Wed, Jun 10, 2009 at 11:18 PM, Tom B <seileef at gmail.com> wrote:

>
> Hi,
>
> It turns outs that stitching together Google Static Maps images is indeed
> in
> violation of the Google Maps ToS.  See 10.2 of:
> http://code.google.com/apis/maps/terms.html
>
> Does anyone happen to have any other ideas of how to achieve this goal
> without violating the ToS?  My guess is that it's not possible, but if
> anyone has any ideas about it, that'd be great.
>
> Thanks,
> Tom
>
>
> Tom B wrote:
> >
> > OK, this has been pretty straightforward (thanks for the tips, Gregor).
> > The one issue I'm having is calculating the latitude value of the tiles'
> > centers while accounting for the change in distance per latitude degree
> > while traveling north-south.  The code I'm using now calculates a
> > "latitude degrees per pixel" value, which is an alright approximation for
> > the whole map at very high zoom levels, but at lower zoom levels it isn't
> > accurate, and the resulting tile rows begin to drift apart.  I have very
> > little GIS experience, so I'm a bit lost on where to start with
> > calculating these centers accurately.
> >
> > Any ideas of how to approach this?  I'm guessing that trig-related
> > expressions will be involved.
> >
> > To show how this is currently set up, my code is:
> >
> > // $width and $height - the pixel dimensions of the map
> > // $bounds - the EPSG:4326 BBOX of the map
> > function add_gmaps_layer($image, $width, $height, $bounds, $zoom, $key,
> > $temp_dir){
> >       $base_url =
> > '
> http://maps.google.com/staticmap?key='.$key.'&sensor=false&size=640x640&zoom='.$zoom<http://maps.google.com/staticmap?key=%27.$key.%27&sensor=false&size=640x640&zoom=%27.$zoom>
> ;
> >       $num_cols = ceil($width/640);
> >       $num_rows = ceil($height/640);
> >       list($left, $bottom, $right, $top) = split(',', $bounds);
> >       $lon_per_px = abs($right-$left)/$width;
> >       $lat_per_px = abs($top-$bottom)/$height;
> >       for($i=0; $i<$num_cols; $i++){
> >               for($j=0; $j<$num_rows; $j++){
> >                       // Calculate the tile's center, relative to the
> bottom right corner of
> > the map
> >                       $center_x = 320 + ($i*640);
> >                       $center_y = 320 + ($j*640);
> >                       // Calculate the lon, lat of the tile
> >                       $center_lon = $right - ($center_x*$lon_per_px);
> >                       $center_lat = $bottom + ($center_y*$lat_per_px);
> >                       $url =
> $base_url.'&center='.$center_lat.','.$center_lon;
> >                       $x = $width - (($i+1)*640);
> >                       $y = $height - (($j+1)*640);
> >                       // Blit the tile onto the main image width a
> displacement of $x, $y
> >                       $image = blit_from_url($image, $url, $x, $y,
> $temp_dir);
> >               }
> >       }
> >       return $image;
> > }
> >
> >
> > Gregor at HostGIS wrote:
> >>
> >> Tom B wrote:
> >>> Has anyone had a chance to try this out?  Gregor, any luck with getting
> >>> R&D
> >>> funding, by any chance?  If not, I might go ahead and take a crack at
> >>> it,
> >>> since it is something our map will eventually need.
> >>
> >> The customer wasn't up for it when I presented it to him, so I have
> >> nothing to show on this. Sorry.
> >>
> >> The way I figure to render it, would be:
> >>
> >> Take image width, divide by 640 rounding up.
> >> Take image height, divide by 640 rounding up.
> >> foreach w in width:
> >>    foreach h in height:
> >>      figure up center latlng (320,320) based on bbox and pixel position
> >>      figure URL
> >>      fetch image
> >>      blit it onto the canvas
> >>
> >> I have existing code in the Wiki ("Printing" page) for doing this in
> >> PHP, using URLs that are provided by the client. That at least shows the
> >> blitting and alpha code.
> >>
> >> --
> >> HostGIS, Open Source solutions for the global GIS community
> >> Greg Allensworth - SysAdmin, Programmer, GIS Person, Security
> >> Network+   Server+   A+   Security+
> >> _______________________________________________
> >> Users mailing list
> >> Users at openlayers.org
> >> http://openlayers.org/mailman/listinfo/users
> >>
> >>
> >
> >
>
> --
> View this message in context:
> http://n2.nabble.com/Saving-with-a-Google-Maps-base-layer-tp2736685p3058442.html
> Sent from the OpenLayers Users mailing list archive at Nabble.com.
>
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