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List: mapserver-dev
Subject: [mapserver-dev] Fwd: mapresample algorithm
From: fred p <mapoubelle22 () gmail ! com>
Date: 2011-11-03 15:28:42
Message-ID: CADzX+2V8qwSW1SY4rJeBPczwsGViLSmFGb1OWABW8SFN+8sQ2g () mail ! gmail ! com
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[Attachment #2 (multipart/alternative)]
Hello,
Nobody has replied to the following message. I would be grateful if
somebody could take some minutes to express his feeling about the behavior
I described that seems strange to me.
Thanks.
---------- Message transféré ----------
De : fred p <mapoubelle22@gmail.com>
Date : 12 octobre 2011 13:47
Objet : mapresample algorithm
À : mapserver-dev@lists.osgeo.org
Hello,
I want to serve a source image via a WMS through mapserver but I sometimes
get a very low resolution due to the algorithm applied in the
msResampleGDALToMap method in mapresample.c. This occurs when I request a
much larger area and a much lower resolution than the ones of the source
image.
For example, here is an extract of the gdalinfo :
Size is 8192, 6144
Coordinate System is:
PROJCS["unnamed",
GEOGCS["unnamed ellipse",
DATUM["unknown",
SPHEROID["unnamed",6378160,298.2539162964669]],
PRIMEM["Greenwich",0],
UNIT["degree",0.0174532925199433]],
PROJECTION["Polar_Stereographic"],
PARAMETER["latitude_of_origin",60],
PARAMETER["central_meridian",0],
PARAMETER["scale_factor",1],
PARAMETER["false_easting",0],
PARAMETER["false_northing",0],
UNIT["metre",1,
AUTHORITY["EPSG","9001"]]]
Origin = (-4937982.331945824436843,-1228156.832371974131092)
Pixel Size = (1093.000000000000000,-1093.000000000000000)
Corner Coordinates:
Upper Left (-4937982.332,-1228156.832) ( 76d 1'58.80"W, 43d45'32.40"N)
Lower Left (-4937982.332,-7943548.832) ( 31d51'59.40"W, 13d34'43.86"N)
Upper Right ( 4015873.668,-1228156.832) ( 72d59'42.10"E, 51d11'57.65"N)
Lower Right ( 4015873.668,-7943548.832) ( 26d49'8.23"E, 16d20'22.12"N)
Here is an extract of the WMS request :
&width=885&height=443&bbox=-177,-88.6,177,88.6&
The algorithm transforms the requested bbox in the SRS of the origin image
and calculates the size in the source image (sOrigSrcExtent) of this bbox
before evaluating sDummyMap.cellsize from sOrigSrcExtent. As a result I get
a very low nLoadImgXSize an nLoadImgYSize (respectivly 8 and 6 !). Wouldn't
it be possible to improve this algorithm by calculating sDummyMap.cellsize
from the extent of the origin image instead of from the extent of the
transformed requested bbox ?
For now I have identified 2 alternatives (maybe there are others ?) that
are not really convenient :
1 - calculate while handling any request an adequate oversample_ratio
(doesn't simplify the code of my mapscript ;))
2 - use the processing option "load_whole_image" but the response time is
affected.
Thanks in advance for your response / help.
<http://int.ask.com/web?siteid=10000861&webqsrc=999&l=dis&q=mapresample>
<http://int.ask.com/web?siteid=10000861&webqsrc=999&l=dis&q=feedback>
[Attachment #5 (text/html)]
Hello,<br>Nobody has replied to the following message. I would be grateful if \
somebody could take some minutes to express his feeling about the behavior I \
described that seems strange to me.<br>Thanks.<br><br><div \
class="gmail_quote">
---------- Message transféré ----------<br>De : <b class="gmail_sendername">fred \
p</b> <span dir="ltr"><<a \
href="mailto:mapoubelle22@gmail.com">mapoubelle22@gmail.com</a>></span><br>Date : \
12 octobre 2011 13:47<br>Objet : mapresample algorithm<br> À : <a \
href="mailto:mapserver-dev@lists.osgeo.org">mapserver-dev@lists.osgeo.org</a><br><br><br>Hello,<br><br>I \
want to serve a source image via a WMS through mapserver but I sometimes get a very \
low resolution due to the algorithm applied in the msResampleGDALToMap method in \
mapresample.c. This occurs when I request a much larger area and a much lower \
resolution than the ones of the source image.<br>
<br>For example, here is an extract of the gdalinfo :<br><br>Size is 8192, \
6144<br>Coordinate System is:<br>PROJCS["unnamed",<br> \
GEOGCS["unnamed ellipse",<br> DATUM["unknown",<br> \
SPHEROID["unnamed",6378160,298.2539162964669]],<br> \
PRIMEM["Greenwich",0],<br> \
UNIT["degree",0.0174532925199433]],<br> \
PROJECTION["Polar_Stereographic"],<br> \
PARAMETER["latitude_of_origin",60],<br> \
PARAMETER["central_meridian",0],<br>
PARAMETER["scale_factor",1],<br> \
PARAMETER["false_easting",0],<br> \
PARAMETER["false_northing",0],<br> UNIT["metre",1,<br> \
AUTHORITY["EPSG","9001"]]]<br>
Origin = (-4937982.331945824436843,-1228156.832371974131092)<br>Pixel Size = \
(1093.000000000000000,-1093.000000000000000)<br>Corner Coordinates:<br>Upper Left \
(-4937982.332,-1228156.832) ( 76d 1'58.80"W, 43d45'32.40"N)<br>
Lower Left (-4937982.332,-7943548.832) ( 31d51'59.40"W, \
13d34'43.86"N)<br>Upper Right <a href="tel:%28%204015873.668" \
value="+14015873668" target="_blank">( 4015873.668</a>,-1228156.832) ( \
72d59'42.10"E, 51d11'57.65"N)<br> Lower Right <a \
href="tel:%28%204015873.668" value="+14015873668" target="_blank">( \
4015873.668</a>,-7943548.832) ( 26d49'8.23"E, 16d20'22.12"N)<br> \
<br>Here is an extract of the WMS request \
:<br><br>&width=885&height=443&bbox=-177,-88.6,177,88.6&<br><br>The \
algorithm transforms the requested bbox in the SRS of the origin image and calculates \
the size in the source image (sOrigSrcExtent) of this bbox before evaluating \
sDummyMap.cellsize from sOrigSrcExtent. As a result I get a very low nLoadImgXSize an \
nLoadImgYSize (respectivly 8 and 6 !). Wouldn't it be possible to improve this \
algorithm by calculating sDummyMap.cellsize from the extent of the origin image \
instead of from the extent of the transformed requested bbox ?<br>
<br>For now I have identified 2 alternatives (maybe there are others ?) that are not \
really convenient :<br>1 - calculate while handling any request an adequate \
oversample_ratio (doesn't simplify the code of my mapscript ;))<br>
2 - use the processing option "load_whole_image" but the response time is \
affected.<br><br>Thanks in advance for your response / help.<br><br> <img \
src="http://www.qtl.co.il/img/copy.png" title="Copy Selction"><a \
href="http://int.ask.com/web?siteid=10000861&webqsrc=999&l=dis&q=mapresample" \
title="Search With Ask" target="_blank"><img \
src="http://www.ask.com/favicon.ico"></a><img \
src="http://translate.google.com/favicon.ico" title="Translate With Google">
</div><br><style>
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position: absolute;
border: 1px solid #cccccc;
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<img src="http://www.qtl.co.il/img/copy.png" title="Copy Selction"><a \
href="http://int.ask.com/web?siteid=10000861&webqsrc=999&l=dis&q=feedback" \
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