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<DIV><SPAN class=807322014-04052005><FONT face=Arial
size=2>Greetings,</FONT></SPAN></DIV>
<DIV><SPAN class=807322014-04052005><FONT face=Arial
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=807322014-04052005><FONT face=Arial size=2>I am new to
GeoTIFF. I am a meteorologist, and would say I have a better than average
understanding of projections than many meteorologists, but still am unsure of a
lot of the cartographic terminology used in the GeoTIFF
specification. I am currently able to create georeferenced images of
gridded data sets using an application called IDL (Interactive Data Language, a
4DL used for data visualization and exploration). My gridded data sets are
generally either Lambert Conformal, Polar Stereographic, or Mercator
projections. For these data sets, I have routines that allow me to define
the grid based on 1 known point in the grid, defined by its (i,j) index and a
latitude and longitude, the "standard longitude" (the longitude line that is
parallel to the grids y-axis), the standard latitude(s) (the latitude(s) at
which the grid spacing is exact), the grid point spacing (in meters) at the
standard latitude, and the dimensions of the grid. From that definition, I
am able to compute the latitude/longitude of any I/J point and vice versa.
In my convention, the grid (i,j) values originate at the southwest corner of the
grid. </FONT></SPAN></DIV>
<DIV><SPAN class=807322014-04052005><FONT face=Arial
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=807322014-04052005><FONT face=Arial size=2>From this
definition, I am also able to define a an IDL "mapping" window from this
information, such that IDL has a georeferenced canvas upon which it can contour
the data, plot points, etc. Within IDL, I can determine the latitude and
longitude of any pixel location. IDL supports writing GeoTIFFs, but
currently the GeoTIFF tags have to be manually set. My problem is that I
am having trouble figuring out the appropriate values. I have looked at
the GeoTIFF spec and some of the Lambert conformal examples, but still cannot
seem to set things correctly. In particular, the whole concept of "false
northing/easting" has me stumped. I don't know the Pixel scale values,
etc. It would seem that if I can provide one or more "tie points" ,where a
tie point is a known pixel location ( [i,j] in raster units) and the
latitude/longitude, along with the projection parameters (type,
standard_parallels, standard longitude), that everything one needs to establish
a transformation is present, without having to know what the pixel spacing is,
etc. For example, I have a tangent Lambert conformal grid with a standard
longitude of -95.0 deg, standard latitude of 25.0, and a known "cone
factor." I also can provide the latitude/longitude of all 4 corner
points. Is that enough info to encode a geoTIFF, and if so, which
parameters should I be setting? Or, do I have to write some code to
compute things like "false origin", "false easting" etc.?
</FONT></SPAN></DIV>
<DIV><SPAN class=807322014-04052005><FONT face=Arial
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=807322014-04052005><FONT face=Arial size=2>Sorry for the novice
question, but after all my searching I am still not clear. Thanks in
advance for any help you can provide.</FONT></SPAN></DIV>
<DIV><SPAN class=807322014-04052005><FONT face=Arial
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=807322014-04052005><FONT face=Arial size=2>Best
regards,</FONT></SPAN></DIV>
<DIV><SPAN class=807322014-04052005><FONT face=Arial
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=807322014-04052005><FONT face=Arial size=2>Brent
Shaw</FONT></SPAN></DIV></BODY></HTML>