AW: [mapserver-users] "Low-resolution" raster image problem when
usingOpenlayers
kensei3000
kensei3000 at yahoo.com
Thu Jun 30 22:19:04 EDT 2011
Hi Arnd,
I checked the source code for OpenLayers.Layer.MapServer and OpenLayers.Layer.WMS and confirmed the DEFAULT_PARAMS you indicated.
I tried calling MapServer using the DEFAULT_PARAMS for OpenLayers.Layers.MapServer in this url:
http://remotehost/cgi-bin/mapserv?map=/opt/maps/sandbox/mapserver_openlayers_if/sample.map&mode=map&map_imagetype=png
And indeed an 8-bit image was rendered.
I read from the documentation that MapServer can act like a WMS server, which is why OpenLayers.Layers.WMS works with MapServer also.
I believe you have succinctly explained the cause of the image rendering discrepancy.
Problem appears to be solved.
Thanks for all your help. :)
Ken
________________________________
From: Arnd Wippermann <arnd.wippermann at web.de>
To: 'kensei3000' <kensei3000 at yahoo.com>
Cc: mapserver-users at lists.osgeo.org
Sent: Friday, July 1, 2011 6:41 AM
Subject: AW: [mapserver-users] "Low-resolution" raster image problem when usingOpenlayers
You can request tiles from MapServer by a MapServer
cgi request or by a WMS request.
OpenLayers uses this
DEFAULT_PARAMS:
{
mode:
"map",
map_imagetype: "png" // a
8bit png if not otherwise declared in the mapfile
},
for OpenLayers.Layer.MapServer
DEFAULT_PARAMS: { service:
"WMS",
version:
"1.1.1",
request:
"GetMap",
styles:
"",
exceptions:
"application/vnd.ogc.se_inimage",
format:
"image/jpeg"
},
for OpenLayers.Layer.WMS
if you
not specify a imageformat, then the OpenLayers.Layer.MapServer requests a png
and the WMS requests a jpg (if not set
transparent=true).
Arnd
________________________________
Von: kensei3000 [mailto:kensei3000 at yahoo.com]
Gesendet: Donnerstag, 30. Juni 2011 04:58
An: Arnd
Wippermann
Cc: mapserver-users at lists.osgeo.org
Betreff: Re:
AW: [mapserver-users] "Low-resolution" raster image problem when
usingOpenlayers
Hi Arnd,
I see. I used the same 'mapserv' url in both OpenLayers.Layer.WMS and
.MapServer code. The requests were sent to the same remote server. So the
difference must be in the requests. Is it possible that OpenLayers.Layer.WMS
generated a different output url string from the one generated by
OpenLayers.Layer.MapServer?
Ken
________________________________
From: Arnd Wippermann
<arnd.wippermann at web.de>
To: 'kensei3000'
<kensei3000 at yahoo.com>
Cc: mapserver-users at lists.osgeo.org
Sent: Thursday, June 30, 2011 1:15
AM
Subject: AW:
[mapserver-users] "Low-resolution" raster image problem when
usingOpenlayers
Hi
Ken,
Quote :
"Interestingly, if I use the 'mapserv' executable directly in the browser
instead of using OpenLayers API, the image also renders correctly."
There could be no
difference (OpenLayers.Layer.WMS or .MapServer), because with OpenLayers you
only create an url for an image tag (<img src="url">). The response have
to be the same as from the browser directly.
The difference could only
be a result from different requests or the same request to different
servers.
Arnd
________________________________
Von: kensei3000
[mailto:kensei3000 at yahoo.com]
Gesendet: Mittwoch, 29. Juni 2011
09:56
An: Arnd Wippermann
Cc: users at openlayers.org
Betreff: Re: AW: [mapserver-users]
"Low-resolution" raster image problem when
usingOpenlayers
Hi
Arnd,
I
checked the images properties of the tile images using ImageMagick.
tile_topleft_remote.png
has image type "Palette" (8-bit)
tile_topleft_local.png
has image type "TrueColor" (32-bit)
The
results I got seem to correlate with your findings.
Indeed,
it appears that the image rendering between my local pc and the server are
different.
The map
files are exactly same since I sync them in both computers.
The
MapServer versions, however, are different. Here's what I got:
LOCAL:
MapServer version 6.0.0
OUTPUT=GIF OUTPUT=PNG OUTPUT=JPEG SUPPORTS=PROJ SUPPORTS=AGG SUPPORTS=CAIRO
SUPPORTS=FREETYPE SUPPORTS=ICONV SUPPORTS=FRIBIDI SUPPORTS=WMS_SERVER
SUPPORTS=WMS_CLIENT SUPPORTS=WFS_SERVER SUPPORTS=WFS_CLIENT SUPPORTS=WCS_SERVER
SUPPORTS=SOS_SERVER SUPPORTS=FASTCGI SUPPORTS=THREADS SUPPORTS=GEOS
INPUT=POSTGIS INPUT=OGR INPUT=GDAL INPUT=SHAPEFILE
REMOTE:
MapServer version 5.6.1
OUTPUT=GIF OUTPUT=PNG OUTPUT=JPEG OUTPUT=WBMP OUTPUT=SWF OUTPUT=SVG
SUPPORTS=PROJ SUPPORTS=AGG SUPPORTS=FREETYPE SUPPORTS=ICONV SUPPORTS=FRIBIDI
SUPPORTS=WMS_SERVER SUPPORTS=WMS_CLIENT SUPPORTS=WFS_SERVER SUPPORTS=WFS_CLIENT
SUPPORTS=WCS_SERVER SUPPORTS=FASTCGI SUPPORTS=THREADS SUPPORTS=GEOS INPUT=EPPL7
INPUT=POSTGIS INPUT=OGR INPUT=GDAL INPUT=SHAPEFILE
The MapServer executable
in the remote server is an older version (5.6.1) than the one in my pc (6.0.0).
I edited the map files and images in my local pc, then synced them to the
server, so there may be an incompatibility. I checked the Mapserver Migration
Guide (http://mapserver.org/de/MIGRATION_GUIDE.html) and my guess was that the
default OUTPUTFORMAT specifications of both versions could be
different. I did not specify an explicit OUTPUTFORMAT
in my map file.
I created another test.
This time I explicitly defined the OUTPUTFORMAT with the following lines added
to the map file in the remote server:
OUTPUTFORMAT
NAME jpeg
DRIVER "AGG/JPEG"
MIMETYPE "image/jpeg"
IMAGEMODE RGB
EXTENSION "jpg"
END
The result was that the output image
generated by the remote server rendered in TrueColor, similar to the output
image in my local pc. Problem appears to be fixed.
My guess
right now is that the IMAGEMODE parameter above was somehow set to PC256
(i.e. 8-bit color palette) by default.
Interestingly, if I use the 'mapserv'
executable directly in the browser instead of using OpenLayers API, the image
also renders correctly.
EXAMPLE:
http://remotehost/cgi-bin/mapserv?map=/opt/maps/sandbox/mapserver_openlayers_if/sample.map&mode=map
Above 'sample.map' did not
have the OUTPUTFORMAT object explicitly defined.
In another test I ran
using the original 'sample.map' (i.e. no OUTPUTFORMAT object), I edited the
OpenLayers code in the remote server:
//sample.html
FROM:
17
layer = new OpenLayers.Layer.MapServer("World
Map",
TO:
17
layer = new OpenLayers.Layer.WMS("World Map",
I used the generic 'WMS'
layer instead of the 'MapServer' layer. And the result was that the output image
rendered correctly. I am not yet sure why.
I might
need to run additional tests to confirm my findings.
Thanks
for your help in pointing out the discrepancies in the images and in MapServer.
:)
Ken
________________________________
From: Arnd Wippermann
<arnd.wippermann at web.de>
To: 'kensei3000'
<kensei3000 at yahoo.com>
Cc: users at openlayers.org
Sent: Wednesday, June 29, 2011 2:28
AM
Subject: AW:
[mapserver-users] "Low-resolution" raster image problem when
usingOpenlayers
use some image viewer to get information of your
images.
tile_topleft_remote.pngis a 8bit image (256 color image), where only 45
colors used.
tile_topleft_local.png is a 24bit image (16,7 Mill.
colors), where 13274 colors used.
The requests ask for map_imagetype=png. So it
seems, that your mapfiles are different, because the response of the servers
delivers a different image for the same imagetype. Or do you
use different MapServer versions?
The problem has to
be an issue with MapServer and not with
OpenLayers.
Arnd
________________________________
Von: kensei3000
[mailto:kensei3000 at yahoo.com]
Gesendet: Dienstag, 28. Juni 2011
04:32
An: Arnd Wippermann
Cc: users at openlayers.org
Betreff: Re: AW: [mapserver-users]
"Low-resolution" raster image problem when usingOpenlayers
Hi
Arnd,
Thanks
a lot for the tip. I copied the image url of the top-left most tile for both
local pc and remote server tests.
Here is
what I got:
Local:
http://localhost/cgi-bin/mapserv?map=%2Fopt%2Fmaps%2Fsandbox%2Fmapserver_openlayers_if%2Fsample.map&layers=sample_raster&mode=map&map_imagetype=png&mapext=-90+0+0+90&imgext=-90+0+0+90&map_size=256+256&imgx=128&imgy=128&imgxy=256+256
Remote:
http://remotehost/cgi-bin/mapserv?map=%2Fopt%2Fmaps%2Fsandbox%2Fmapserver_openlayers_if%2Fsample.map&layers=sample_raster&mode=map&map_imagetype=png&mapext=-180+-90+0+90&imgext=-180+-90+0+90&map_size=256+256&imgx=128&imgy=128&imgxy=256+256
The only significant
difference of the two urls appear to be the 'mapext' and 'imgext' parameters.
When I checked the resulting images after inputting the urls in the browser, I
noticed that the tile images had different sizes and positions. I believe this
was due to the said parameters. I tried changing the 'mapext' and 'imagext'
parameters of the server test url to match that of the local test url, and
indeed the size and position of the remote server tile image changed. However, I
am still unable to figure out what causes the color distortion or "downsampling"
of the image in the remote server.
For further reference,
I've attached the tile images I got using the above urls.
Here is the openlayers
code I used. It is the same for both local and remote server tests except for
the host in line 18.
//sample.html
1<html
xmlns="http://www.w3.org/1999/xhtml">
2 <head>
3 <style
type="text/css">
4 #map
{
5
width: 1024px;
6
height: 768px;
7
border: 1px solid black;
8 }
9 </style>
10 <script
src="http://openlayers.org/dev/lib/OpenLayers.js"></script>
11 <script
type="text/javascript">
12
<!--
13 var map,
layer;
14
15 function
init(){
16
map = new OpenLayers.Map( 'map' );
17
layer = new OpenLayers.Layer.MapServer("World Map",
18
"http://localhost/cgi-bin/mapserv",
19
{map:
'/opt/maps/sandbox/mapserver_openlayers_if/sample.map', layers:
'sample_raster'});
20
map.addLayer(layer);
21
map.zoomToMaxExtent();
22 }
23 //
-->
24 </script>
25 </head>
26 <body
onload="init()">
27 <div
id="map"></div>
28 </body>
29</html>
And below is the common
.map file I created with the help of the Quantum GIS Mapserver Export
tool.
The raster image has an
associated World file (.wld) for georeferencing.
1# Map file created from QGIS project
file /var/maps/sandbox/mapserver_openlayers_if/sample.qgs
2# Edit this file to customize for your
map interface
3# (Created with PyQgis MapServer
Export plugin)
4MAP
5 NAME "QGIS-MAP"
6 # Map image size
7 SIZE 8180 4930
8 UNITS meters
9
10 EXTENT -86.515507 -50.290979
88.076495 48.225271
11 PROJECTION
12 'proj=longlat'
13 'ellps=WGS84'
14
'towgs84=0,0,0,0,0,0,0'
15 'no_defs'
16 END
17
18 # Background color for the map
canvas -- change as desired
19 IMAGECOLOR 255 255 255
20 IMAGEQUALITY 95
21 IMAGETYPE jpeg
22
23 # Legend
24 LEGEND
25 IMAGECOLOR 255 255
255
26 STATUS ON
27 KEYSIZE 18 12
28 LABEL
29 TYPE BITMAP
30 SIZE MEDIUM
31 COLOR 0 0 89
32 END
33 END
34
35 # Web interface definition. Only
the template parameter
36 # is required to display a map.
See MapServer documentation
37 WEB
38 # Set IMAGEPATH to the
path where MapServer should
39 # write its output.
40 IMAGEPATH '/tmp/'
41
42 # Set IMAGEURL to the url
that points to IMAGEPATH
43 # as defined in your web
server configuration
44 IMAGEURL '/tmp/'
45
46 #Scale range at which web
interface will operate
47 # Template and
header/footer settings
48 # Only the template
parameter is required to display a map. See MapServer documentation
49 TEMPLATE
'fooOnlyForWMSGetFeatureInfo'
50 END
51
52 LAYER
53 NAME
'sample_raster'
54 TYPE RASTER
55 DUMP true
56 TEMPLATE
fooOnlyForWMSGetFeatureInfo
57 EXTENT -86.515507 -50.290979
88.076495 48.225271
58 DATA
'sec_field.jpg'
59 STATUS DEFAULT
60 TRANSPARENCY 100
61 PROJECTION
62 'proj=longlat'
63 'ellps=WGS84'
64
'towgs84=0,0,0,0,0,0,0'
65 'no_defs'
66 END
67 END
68
69END
Hope you could provide
further assistance.
Ken
________________________________
From: Arnd Wippermann
<arnd.wippermann at web.de>
To: 'kensei3000'
<kensei3000 at yahoo.com>
Cc: users at openlayers.org
Sent: Tuesday, June 28, 2011 1:53
AM
Subject: AW:
[mapserver-users] "Low-resolution" raster image problem when
usingOpenlayers
hi,
if you do a right click on a tile to get the context menu, you
should be able to copy the url (if the tiles of your server is the most top of
the visible layers). Compare the different urls. If you load them in your
browser you should get a response for a single tile from your
server.
Perhaps that gives you an idea, what goes
wrong.
Arnd
________________________________
Von: mapserver-users-bounces at lists.osgeo.org
[mailto:mapserver-users-bounces at lists.osgeo.org] Im Auftrag von kensei3000
Gesendet: Montag, 27. Juni 2011 05:37
An: mapserver-users at lists.osgeo.org
Betreff: [mapserver-users]
"Low-resolution" raster image problem when usingOpenlayers
Hi!
I am trying to use MapServer as a WMS layer in Openlayers. I setup the
MapServer in our server machine, using my own PC as the test client. I created a
simple .map file in our server that contains one raster image. Using the
mapserver tool 'mapserv' in a URL string, I was able to load the output map with
full resolution correctly in a browser (Google Chrome). However, when I tried to
load the map using a simple Openlayers script (HMTL) which I created on our
server (accessible via browser), the map image appeared to have a much
lower-resolution (i.e. 256-colors only) and was pixelized. Also, I could see
white lines representing the tile edges of the map.
I did another test. This time, I installed MapServer in my own PC. I
created a .map file similar to the one I used in our server, with the same
raster image. I created a similar Openlayers script (HTML) in my own PC, but
this time it would call the MapServer from my own PC. I loaded the script using
a browser and the image displayed correctly with full resolution.
Does anyone have an idea what the problem could be?
I would appreciate any help in this matter.
Thanks in advance! :)
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