The output looks correct in that if the resulting images are each viewed on a
device that has the corresponding DPI resolution, the map scale of 5000 would
be correct if physically measured with a ruler.
What exactly do you think is incorrect? The math behind it goes something like
this:
double metersPerUnit = map->GetMetersPerUnit();
double metersPerPixel = 0.0254 / dpi;
double mappingWidth = imageWidth * metersPerPixel * scale / metersPerUnit;
You can see that the width (and also height) of the visible region will vary
inversely with DPI, if everything else is constant.
Traian
-----Original Message-----
From: [EMAIL PROTECTED] on behalf of simon hope
Sent: Thu 9/6/2007 6:59 PM
To: [email protected]
Cc:
Subject: [mapguide-users] Overriding DPI
Hi,
I'm trying a number of methods for exporting images:
1. I used the MgRenderingService class to produce an image (had to use a
nasty hack to get the current extent as map.GetDataExtent(); doesn't
seem to
work?), but using this method does not give me any control over the
image
dpi.
2. I then sent a request over HTTP directly to the MapAgent CGI - this
gives
me the flexibilty to pass parameters over the URL, however when I set
different DPI values, I always get an image set at 72 dpi. Here is a
sample
of the request:
http://localhost/mapguide/mapagent/mapagent.fcgi?OPERATION=GETMAPIMAGE&VERSION=1.0.0&SESSION=6669fbe4-0000-1000-8000-0013d3c0f8fe_en_C0A801140AFC0AFB0AFA&MAPNAME=Sheboygan&LOCALE=en&FORMAT=PNG&SETVIEWCENTERX=-87.732492&SETVIEWCENTERY=43.743934&SETVIEWSCALE=5000&SETDISPLAYDPI=96&SETDISPLAYWIDTH=1024&SETDISPLAYHEIGHT=768
This URL uses 96 DPI - if i sent the same URL but increased the DPI,
this
has the effect of changing the extent of the actual image, despite
keeping
the other parameters static.
I read on a post that DPI can be overriden "if the session allows it"?
Does
this mean that I have to update the session somewhere?
I have attached three images using different DPI values (96, 300 and
600)
which illustrates the effect.
http://www.nabble.com/file/p12533054/http_request96.png
http_request96.png
http://www.nabble.com/file/p12533054/http_request300.png
http_request300.png
http://www.nabble.com/file/p12533054/http_request600.png
http_request600.png
I have also tried to increase the image width and height as I increase
the
dpi - this maintains the extent of the image, but does not alter the
dpi.
This method also results in some rather strange labelling - the number
of
labels increases per feature.
Cheers
Simon
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http://www.nabble.com/Overriding-DPI-tf4395160s16610.html#a12533054
Sent from the MapGuide Users mailing list archive at Nabble.com.
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