<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">
<HTML>
<HEAD>
<META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=us-ascii">
<META NAME="Generator" CONTENT="MS Exchange Server version 6.5.7652.24">
<TITLE>Help Understanding Building Geo Transformation from scratch.</TITLE>
</HEAD>
<BODY>
<!-- Converted from text/rtf format -->
<P DIR=LTR><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT FACE="OCR A Extended">Hi all,</FONT></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"><FONT FACE="OCR A Extended">I am looking for some advice.</FONT></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"><FONT FACE="OCR A Extended">I have a</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"> <FONT FACE="OCR A Extended">netcdf</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT FACE="OCR A Extended"></FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"> <FONT FACE="OCR A Extended">file that contains meteorology information. I know the number of rows and columns of the data as well as the corner points. The data is cylindrical-equidista</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT FACE="OCR A Extended">nt and un-projected.</FONT></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"><FONT FACE="OCR A Extended">I need to be able to extract data from the grid based on lat-lon information.</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT FACE="OCR A Extended"> Since the data is un-projected</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"> <FONT FACE="OCR A Extended">it would be easy to built a simple ratio based on lat and lon differences between corner points and then using simple ratio math navigate into the grid</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT FACE="OCR A Extended">…</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT FACE="OCR A Extended">However, I was hoping there was a way for GDAL to do this for me</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT FACE="OCR A Extended">.</FONT></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"><FONT FACE="OCR A Extended">Since the</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"> <FONT FACE="OCR A Extended">netcdf</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT FACE="OCR A Extended"></FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"> <FONT FACE="OCR A Extended">cannot</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT FACE="OCR A Extended"> be natively understood by GDAL my assumptions are that I will need to build my own projection</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"> <FONT FACE="OCR A Extended">and create a projection transformer.</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT FACE="OCR A Extended"> </FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"> <FONT FACE="OCR A Extended">Since I am not using GDAL to read the data source it</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"> <FONT FACE="OCR A Extended">would</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT FACE="OCR A Extended"> seem that I can set the hSrcDS dataset to NULL.</FONT></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT FACE="OCR A Extended">GDALDatasetH hSrcDS, hDstDS;</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT FACE="OCR A Extended">char *pszDstWKT = NULL</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT FACE="OCR A Extended">;</FONT></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT FACE="OCR A Extended">const char *pszSrcWKT = NULL;</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT FACE="OCR A Extended">hSrcDS =</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"> <FONT FACE="OCR A Extended">hDstDS = NULL;</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT FACE="OCR A Extended">OGRSpatialReferenceH hDEST;</FONT></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"><FONT FACE="OCR A Extended">hDEST = OSRNewSpatialReference(NULL);</FONT></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"><FONT FACE="OCR A Extended">OSRSetWellKnownGeogCS(hDEST, "WGS84");</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"><FONT FACE="OCR A Extended">OSRExportToWkt(hDEST, &pszDstWKT);</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT FACE="OCR A Extended">OSRExportToWkt(hDEST, &psz</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT FACE="OCR A Extended">Src</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT FACE="OCR A Extended">WKT);</FONT></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"><FONT FACE="OCR A Extended">OSRDestroySpatialReference(hDEST);</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT FACE="OCR A Extended">void *my_transformer = GDALCreateGenImgProjTransformer(</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT FACE="OCR A Extended">NULL</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT FACE="OCR A Extended">,</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT FACE="OCR A Extended"> // Since GDAL is not reading the data-set</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"><FONT FACE="OCR A Extended"> </FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"> <FONT FACE="OCR A Extended">psz</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT FACE="OCR A Extended">Src</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT FACE="OCR A Extended">WKT</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT FACE="OCR A Extended">,</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT FACE="OCR A Extended"> // WGS84 is unprojected</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"><FONT FACE="OCR A Extended"> NULL,</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT FACE="OCR A Extended"> // There is no output</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"><FONT FACE="OCR A Extended"> pszDstWKT,</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT FACE="OCR A Extended"> // This is the big question? What should be here?</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"><FONT FACE="OCR A Extended"> FALSE, 0.0, 0);</FONT></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"><FONT FACE="OCR A Extended">// Test the corner point. The output should be 0, 0 since this is the origin of the grid</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"><FONT FACE="OCR A Extended">double x_coord = -127.0;</FONT></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"><FONT FACE="OCR A Extended">double y_coord = 51.0;</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"><FONT FACE="OCR A Extended">// Transform.</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT FACE="OCR A Extended">int my_result = GDALGenImgProjTransform(my_transformer, TRUE, 1, &x_coord, &y_coord,</FONT></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"><FONT FACE="OCR A Extended"> NULL, &projSuccess);</FONT></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"><FONT FACE="OCR A Extended">Not unexpectedly the results of x_coord, and y_coord are the original values. What I don</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT FACE="OCR A Extended">’</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT FACE="OCR A Extended">t understand</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT FACE="OCR A Extended"> is what parameters should be passed into</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"> <FONT FACE="OCR A Extended">GDALCreateGenImgProjTransformer</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT FACE="OCR A Extended"></FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"> <FONT FACE="OCR A Extended">when what I want as output is the</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"> <FONT FACE="OCR A Extended">Cartesian</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT FACE="OCR A Extended"> coordinates</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT FACE="OCR A Extended"> in I,J format that indicate how I am supposed to index into my 2 dimensional array of data.</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"><FONT FACE="OCR A Extended">Thanks in advance for the help,</FONT></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"><FONT FACE="OCR A Extended">Bill</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"></SPAN></P>
</BODY>
</HTML>