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<P><SPAN LANG="en-ca"><FONT SIZE=2 FACE="Arial">Hi,</FONT></SPAN>
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<P><SPAN LANG="en-ca"><FONT SIZE=2 FACE="Arial">I am trying to specify an oblique Mercator projection using proj.4 in GRASS.</FONT></SPAN>
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<P><SPAN LANG="en-ca"><FONT SIZE=2 FACE="Arial">I am looking for some advice about the valid range of the parameters lat_1, lat_2, etc.</FONT></SPAN>
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<P><SPAN LANG="en-ca"><FONT SIZE=2 FACE="Arial">I am trying to specify an "omerc" as follows:</FONT></SPAN>
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<P><SPAN LANG="en-ca"><FONT SIZE=2 FACE="Arial">></FONT></SPAN><SPAN LANG="en-us"><FONT SIZE=2 FACE="Courier New">+proj=omerc +lat_0=45.1875000000 +lat_1=-20.0000000000</FONT></SPAN>
<BR><SPAN LANG="en-us"><FONT SIZE=2 FACE="Courier New">> +lat_2=20.0000000000 +lon_0=0.0000000000 +lon_1=-120.0000000000 </FONT></SPAN>
<BR><SPAN LANG="en-us"><FONT SIZE=2 FACE="Courier New">> +lon_2=-60.0000000000 +k_0=1.0000000000 +no_uoff +rot_conv +a=6378137</FONT></SPAN>
<BR><SPAN LANG="en-us"><FONT SIZE=2 FACE="Courier New">> +rf=298.257223563 +no_defs +towgs84=0.000,0.000,0.000</FONT></SPAN>
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<P><SPAN LANG="en-us"><FONT SIZE=2 FACE="Courier New">GRASS support said that absolute value of lat_0 must be less than 36. Sure enough when I put lat_0 equal 35, proj worked. BUT then I wanted to change the other parameter lat_1, Lat_2, etc. to achieve the required rotation. I would like:</FONT></SPAN></P>
<P><SPAN LANG="en-us"><FONT SIZE=2 FACE="Courier New">Lat_1 = -20</FONT></SPAN>
<BR><SPAN LANG="en-us"><FONT SIZE=2 FACE="Courier New">Lat_2 = 23</FONT></SPAN><SPAN LANG="en-ca"></SPAN>
<BR><SPAN LANG="en-us"><FONT SIZE=2 FACE="Courier New">Lon_1 = -120</FONT></SPAN>
<BR><SPAN LANG="en-us"><FONT SIZE=2 FACE="Courier New">Lon_2 = 45</FONT></SPAN>
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<P><SPAN LANG="en-us"><FONT SIZE=2 FACE="Courier New">(I estimated these parameters by doing a reprojection of my dataset in Global Mapper)</FONT></SPAN>
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<P><SPAN LANG="en-us"><FONT SIZE=2 FACE="Courier New">But proj fails.</FONT></SPAN>
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<P><SPAN LANG="en-us"><FONT SIZE=2 FACE="Courier New">On a related note, what is the accepted range of the +alpha parameter in the alternative specification of omerc?</FONT></SPAN>
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<P><SPAN LANG="en-us"><FONT SIZE=2 FACE="Courier New">Any advice would be appreciated,</FONT></SPAN>
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<BR><SPAN LANG="en-us"><FONT SIZE=2 FACE="Courier New">Garret Duffy.</FONT></SPAN>
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