Hello all, this is my first post on this list, first of all I want to congratulate anybody involved in this fantastic library !
<br><br>I have an issue that is fixed with a workaround but I want to avoid this workaround, here it is :
<br><br>I'm using gdalwarp to reproject imagery from EPSG:21781 (CH 1903) to Google Maps (mercator based) projection.
<br><br>Currently I have been using for -t_srs the suggestion from this blog entry <a href="http://www.sharpgis.net/post/2007/07/26/The-Microsoft-Live-Maps-and-Google-Maps-projection.aspx" target="_top" rel="nofollow">http://www.sharpgis.net/post/2007/07/26/The-Microsoft-Live-Maps-and-Google-Maps-projection.aspx</a><br>
<br>so
<br><br>+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0
<br>+y_0=0 +k=1.0 +units=m +nadgrids=@null +no_defs
<br><br>which defines a perfect sphere(not ellipsoid) but i am not happy with
<br>the results because :
<br>- if i am transforming the bounds of image from CH1903 to WGS84 and
<br>then to Google Maps pixel coordinate system, the result will be a
<br>parallelogram (it is normal, the image will be distorted from CH1903
<br>to Mercator) that can be included in a box with a pair of width/height in pixels
<br>- if i am using gdalwarp the result will be a distorted image (again
<br>it's normal) with another pair of width/height.
<br><br>The expected result after tis 2 operations would be 2 pairs of
width/height WITH SAME ration width/height. However, this issue can be
fixed by FORCING the gdalwarp "-ts width
<br>height" parameter and imagery it's just drawn fine.
<br><br>So my question is, in order not to do this workaround, can you tell me
<br>if you use another -t_srs value, and if yes, which one ?
<br><br>I suppose that should be different for each zoom level, as
GoogleMaps does use different radius for each zoom level. (on zoom
level 0 the imagery is drawn in a single tile 256x256 pixels, so the
radius will be circumference/(2*pi()) pixels , on zoom 1 :
circumference is 512 px, then radius is 2 times bigger than zoom level
0, etc)
<br><br>Thank you in advance,
<br>Vasile Cotovanu