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<DIV>Hi all,</DIV>
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<DIV>I am trying to figure out the possible displacement by using a Lon/Lat pair mistakenly. Suppose we have a coordinate based on Clarke1866 (in ESRI's term it is GCS_Assumed_Geographic_1). This ellipsoid can be found in many US Census data. If someone uses this pair as if it is based on a Perfect Sphere (likely R=6370997.0m), what's the possible error in (X,Y) by Lambert Conformal Projection? That's what I am trying to figure out. So, I wrote a BAT file (I am using a PROJ.4 utilities on XP by compiling it with MinGW and datum shift tables) to compute it. Steps are following: I assume that the given value is based on Clarke1866. So I transformed it into a Lat/Lon on a Perfect Sphere. Then I performed LCC projection for both pairs.</DIV>
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<DIV>----------------------------------------------------------------------</DIV>
<DIV>@cs2cs +proj=longlat +ellps=clrk66 +datum=NAD27 +towgs84=-3,142,183,0,0,0,0 +to +proj=latlong +ellps=sphere +R=6370997 +towgs84=0,0,0 +no_def -f "%%f2" -w9 MonLonLat > MonLonLat.Clarke1866ToSphere<BR>@cs2cs +proj=longlat +ellps=clrk66 +datum=NAD27 +towgs84=-3,142,183,0,0,0,0 +to +proj=latlong +ellps=sphere +R=6370997 +towgs84=0,0,0 +no_def -f "%%f2" -w9 MonLonLat </DIV>
<DIV>@proj +proj=lcc +lat_1=60.0 +lat_2=30.0 +lat_0=40.0 +lon_0=-100.0 +x_0=0 +y_0=0 +ellps=sphere +R=6370997 -f "%%f2" -w9 MonLonLat</DIV>
<DIV>@proj +proj=lcc +lat_1=60.0 +lat_2=30.0 +lat_0=40.0 +lon_0=-100.0 +x_0=0 +y_0=0 +ellps=sphere +R=6370997 -f "%%f2" -w9 MonLonLat.Clarke1866ToSphere<BR>----------------------------------------------------------------------</DIV>
<DIV>I added a duplicate cs2cs line just because to print out the result of first line on screen as well as to store in a file.</DIV>
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<DIV>The file "MonLonLat" has this value</DIV>
<DIV>-84 33. 0</DIV>
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<DIV>Then I got these outputs. </DIV>
<DIV>-84.0000002 32.8244522 834.0192882 ==> it is also stored in MonLonLat.Clarke1866ToSphere<BR>1464716.5725192 -614514.0442942 0<BR>1468546.7535622 -633426.1117132 834.0192882 ==> by using MonLonLat.Clarke1866ToSphere</DIV>
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<DIV>The first line indicating that no serious shift in Lon value as we can expect. But the lat value comes out significantly different then the original value and it ended up about 20 km difference!</DIV>
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<DIV>Is anyone willing to confirm that PROJ4 gives the correct answer to my question? Thank you.</DIV></BODY></HTML>