<html xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns:m="http://schemas.microsoft.com/office/2004/12/omml" xmlns="http://www.w3.org/TR/REC-html40">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<meta name="Title" content="">
<meta name="Keywords" content="">
<meta name="Generator" content="Microsoft Word 15 (filtered medium)">
<style><!--
/* Font Definitions */
@font-face
{font-family:"Cambria Math";
panose-1:2 4 5 3 5 4 6 3 2 4;}
@font-face
{font-family:Calibri;
panose-1:2 15 5 2 2 2 4 3 2 4;}
/* Style Definitions */
p.MsoNormal, li.MsoNormal, div.MsoNormal
{margin:0in;
margin-bottom:.0001pt;
font-size:12.0pt;
font-family:"Times New Roman";}
a:link, span.MsoHyperlink
{mso-style-priority:99;
color:#0563C1;
text-decoration:underline;}
a:visited, span.MsoHyperlinkFollowed
{mso-style-priority:99;
color:#954F72;
text-decoration:underline;}
p
{mso-style-priority:99;
mso-margin-top-alt:auto;
margin-right:0in;
mso-margin-bottom-alt:auto;
margin-left:0in;
font-size:12.0pt;
font-family:"Times New Roman";}
p.MsoListParagraph, li.MsoListParagraph, div.MsoListParagraph
{mso-style-priority:34;
margin-top:0in;
margin-right:0in;
margin-bottom:0in;
margin-left:.5in;
margin-bottom:.0001pt;
font-size:12.0pt;
font-family:"Times New Roman";}
span.EmailStyle18
{mso-style-type:personal-reply;
font-family:Calibri;
color:windowtext;}
span.msoIns
{mso-style-type:export-only;
mso-style-name:"";
text-decoration:underline;
color:teal;}
.MsoChpDefault
{mso-style-type:export-only;
font-size:10.0pt;}
@page WordSection1
{size:8.5in 11.0in;
margin:1.0in 1.0in 1.0in 1.0in;}
div.WordSection1
{page:WordSection1;}
/* List Definitions */
@list l0
{mso-list-id:1683896704;
mso-list-type:hybrid;
mso-list-template-ids:1817758924 67698705 67698713 67698715 67698703 67698713 67698715 67698703 67698713 67698715;}
@list l0:level1
{mso-level-text:"%1\)";
mso-level-tab-stop:none;
mso-level-number-position:left;
text-indent:-.25in;}
@list l0:level2
{mso-level-number-format:alpha-lower;
mso-level-tab-stop:none;
mso-level-number-position:left;
text-indent:-.25in;}
@list l0:level3
{mso-level-number-format:roman-lower;
mso-level-tab-stop:none;
mso-level-number-position:right;
text-indent:-9.0pt;}
@list l0:level4
{mso-level-tab-stop:none;
mso-level-number-position:left;
text-indent:-.25in;}
@list l0:level5
{mso-level-number-format:alpha-lower;
mso-level-tab-stop:none;
mso-level-number-position:left;
text-indent:-.25in;}
@list l0:level6
{mso-level-number-format:roman-lower;
mso-level-tab-stop:none;
mso-level-number-position:right;
text-indent:-9.0pt;}
@list l0:level7
{mso-level-tab-stop:none;
mso-level-number-position:left;
text-indent:-.25in;}
@list l0:level8
{mso-level-number-format:alpha-lower;
mso-level-tab-stop:none;
mso-level-number-position:left;
text-indent:-.25in;}
@list l0:level9
{mso-level-number-format:roman-lower;
mso-level-tab-stop:none;
mso-level-number-position:right;
text-indent:-9.0pt;}
ol
{margin-bottom:0in;}
ul
{margin-bottom:0in;}
--></style>
</head>
<body bgcolor="white" lang="EN-US" link="#0563C1" vlink="#954F72">
<div class="WordSection1">
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri">Hi Even,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri"> I think I have figured out how the GeoLocTransformer works. Dumped out the backmap and might have some changes.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri"><o:p> </o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l0 level1 lfo1"><![if !supportLists]><span style="font-size:11.0pt;font-family:Calibri"><span style="mso-list:Ignore">1)<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="font-size:11.0pt;font-family:Calibri">Rounding up to the nearest integer is definitely the issue here.
<o:p></o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l0 level1 lfo1"><![if !supportLists]><span style="font-size:11.0pt;font-family:Calibri"><span style="mso-list:Ignore">2)<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="font-size:11.0pt;font-family:Calibri">I’m going to try this first – maybe a weighted approach will be better. For now, if a pixel falls in the middle of square – I’m going to add it to all of the 4 vertices. Then
average all the data that went into a pixel of the backmap.<o:p></o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l0 level1 lfo1"><![if !supportLists]><span style="font-size:11.0pt;font-family:Calibri"><span style="mso-list:Ignore">3)<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="font-size:11.0pt;font-family:Calibri">For the regular grid tests, if this shows improvement (hopefully) – I can share the implementation and we can possibly discuss about adding a weighting scheme. I don’t want to
increase the runtime too much by adding complexity.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri">Piyush<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri"><o:p> </o:p></span></p>
<div style="border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in">
<p class="MsoNormal"><b><span style="font-family:Calibri;color:black">From: </span>
</b><span style="font-family:Calibri;color:black">Even Rouault <even.rouault@spatialys.com><br>
<b>Date: </b>Thursday, September 28, 2017 at 2:56 AM<br>
<b>To: </b>"gdal-dev@lists.osgeo.org" <gdal-dev@lists.osgeo.org><br>
<b>Cc: </b>"Agram, Piyush S (334D)" <Piyush.Agram@jpl.nasa.gov><br>
<b>Subject: </b>Re: [gdal-dev] Geolocation arrays - location interpretation<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
<p style="margin:0in;margin-bottom:.0001pt;-qt-block-indent:0;-qt-user-state:0">On jeudi 28 septembre 2017 02:14:53 CEST Agram, Piyush S (334D) wrote:<o:p></o:p></p>
<p style="margin:0in;margin-bottom:.0001pt;-qt-block-indent:0;-qt-user-state:0">> Hi,<o:p></o:p></p>
<p style="margin:0in;margin-bottom:.0001pt;-qt-block-indent:0;-qt-user-state:0">> I’m trying to track down systematic pixel shift effects observed with<o:p></o:p></p>
<p style="margin:0in;margin-bottom:.0001pt;-qt-block-indent:0;-qt-user-state:0">> warping data using geolocation arrays:<o:p></o:p></p>
<p style="margin:0in;margin-bottom:.0001pt;-qt-block-indent:0;-qt-user-state:0">> https://trac.osgeo.org/gdal/ticket/6959<o:p></o:p></p>
<p style="margin:0in;margin-bottom:.0001pt;-qt-block-indent:0;-qt-user-state:0">>
<o:p></o:p></p>
<p style="margin:0in;margin-bottom:.0001pt;-qt-block-indent:0;-qt-user-state:0">> Essentially, the same data (image and location) provided as geolocation<o:p></o:p></p>
<p style="margin:0in;margin-bottom:.0001pt;-qt-block-indent:0;-qt-user-state:0">> arrays is warped to a different output depending on how the arrays are laid<o:p></o:p></p>
<p style="margin:0in;margin-bottom:.0001pt;-qt-block-indent:0;-qt-user-state:0">> out – WESN, WENS, EWSN, EWNS.<o:p></o:p></p>
<p style="margin:0in;margin-bottom:.0001pt;-qt-block-indent:0;-qt-user-state:0">Gdalwarp produces least shift in warped data<o:p></o:p></p>
<p style="margin:0in;margin-bottom:.0001pt;-qt-block-indent:0;-qt-user-state:0">> when the input arrays themselves are oriented WENS.
<o:p></o:p></p>
<p style="margin:0in;margin-bottom:.0001pt;-qt-block-indent:0;-qt-user-state:0">> Is there a definitive definition for interpretation of lat,lon,value when<o:p></o:p></p>
<p style="margin:0in;margin-bottom:.0001pt;-qt-block-indent:0;-qt-user-state:0">> geolocation arrays – i.e, are the lat/lon representative of pixel center<o:p></o:p></p>
<p style="margin:0in;margin-bottom:.0001pt;-qt-block-indent:0;-qt-user-state:0">> (which I think should be the intent)?<o:p></o:p></p>
<p style="margin:0in;margin-bottom:.0001pt;-qt-paragraph-type:empty;-qt-block-indent:0">
<o:p></o:p></p>
<p style="margin:0in;margin-bottom:.0001pt;-qt-block-indent:0;-qt-user-state:0">That's a good question. I would assume that center of pixel would be what is expected in the gdalgeoloc code. I don't see anything explicitly said about that in<o:p></o:p></p>
<p style="margin:0in;margin-bottom:.0001pt;-qt-block-indent:0;-qt-user-state:0">https://trac.osgeo.org/gdal/wiki/rfc4_geolocate<o:p></o:p></p>
<p style="margin:0in;margin-bottom:.0001pt;-qt-paragraph-type:empty;-qt-block-indent:0">
<o:p></o:p></p>
<p style="margin:0in;margin-bottom:.0001pt;-qt-block-indent:0;-qt-user-state:0">During your examination of the code, could you find what was expected ?<o:p></o:p></p>
<p style="margin:0in;margin-bottom:.0001pt;-qt-paragraph-type:empty;-qt-block-indent:0">
<o:p></o:p></p>
<p style="margin:0in;margin-bottom:.0001pt;-qt-block-indent:0;-qt-user-state:0">I assume you are using geolocation transformer with one of the drivers that support reporting geolocation arrays ? One possibility would be an inconsistency in the convention this
driver (or the datasource itself) reports the lon,lat values with what the geolocation transformer expects.<o:p></o:p></p>
<p style="margin:0in;margin-bottom:.0001pt;-qt-paragraph-type:empty;-qt-block-indent:0">
<o:p></o:p></p>
<p style="margin:0in;margin-bottom:.0001pt;-qt-paragraph-type:empty;-qt-block-indent:0">
<o:p></o:p></p>
<p style="margin:0in;margin-bottom:.0001pt;-qt-block-indent:0;-qt-user-state:0">Does GDAL by default assume that the<o:p></o:p></p>
<p style="margin:0in;margin-bottom:.0001pt;-qt-block-indent:0;-qt-user-state:0">> geolocation value corresponds to the top/left of the pixel? Could this<o:p></o:p></p>
<p style="margin:0in;margin-bottom:.0001pt;-qt-block-indent:0;-qt-user-state:0">> confusion result in the observed systematic shift?
<o:p></o:p></p>
<p style="margin:0in;margin-bottom:.0001pt;-qt-block-indent:0;-qt-user-state:0">> Alternately, could the input arrays be reoriented to WENS using VRTs instead<o:p></o:p></p>
<p style="margin:0in;margin-bottom:.0001pt;-qt-block-indent:0;-qt-user-state:0">> of rewriting large raster files?<o:p></o:p></p>
<p style="margin:0in;margin-bottom:.0001pt;-qt-paragraph-type:empty;-qt-block-indent:0">
<o:p></o:p></p>
<p style="margin:0in;margin-bottom:.0001pt;-qt-block-indent:0;-qt-user-state:0">X_DATASET and Y_DATASET can point to any valid GDAL dataset, so a VRT should be possible (and you'll need a VRT to modify the values of X_DATASET and Y_DATASET ;-))<o:p></o:p></p>
<p style="margin:0in;margin-bottom:.0001pt;-qt-paragraph-type:empty;-qt-block-indent:0">
<o:p></o:p></p>
<p style="margin:0in;margin-bottom:.0001pt;-qt-block-indent:0;-qt-user-state:0">Even<o:p></o:p></p>
<p style="margin:0in;margin-bottom:.0001pt;-qt-paragraph-type:empty;-qt-block-indent:0">
<o:p></o:p></p>
<p style="margin:0in;margin-bottom:.0001pt;-qt-block-indent:0;-qt-user-state:0">--
<o:p></o:p></p>
<p style="margin:0in;margin-bottom:.0001pt;-qt-block-indent:0;-qt-user-state:0">Spatialys - Geospatial professional services<o:p></o:p></p>
<p style="margin:0in;margin-bottom:.0001pt;-qt-block-indent:0;-qt-user-state:0">http://www.spatialys.com<o:p></o:p></p>
</div>
</body>
</html>