[mapserver-users] Draw roads WITHOUT anti-aliasing

[Lime, Steve D (MNIT)]

AGG is all about high quality and high performance so aliased output is antithetical. I doubt the author ever thought (or cared) about that as a use case.
Maybe Cairo supports this? I suppose one could write a special rendering backend that only draws aliased lines and bails on most everything else. The algorithm for drawing a line is well known.

________________________________
From: Erik H <erik.h11.01 at gmail.com>
Sent: Monday, October 16, 2017 2:23:33 PM
To: Lime, Steve D (MNIT)
Cc: mapserver-users at lists.osgeo.org
Subject: Re: [mapserver-users] Draw roads WITHOUT anti-aliasing

I don't think we have much use for lines that are one pixel wide.

I'm surprised at how difficult this is; isn't there some driver other than AGG/PNG I could use?



On Mon, Oct 16, 2017 at 2:50 PM, Lime, Steve D (MNIT) <steve.lime at state.mn.us<mailto:steve.lime at state.mn.us>> wrote:
So you really do need 24-bit output. I was looking back through the mailing list archives and it was mentioned back in 2012 that aliased output could be implemented for simple (1 pixel-wide) lines and polygons – so there is hope but I don’t believe (looking through the source) that Thomas ever fully implemented it. In mapagg.cpp there are ifdef’s for a symbol named AGG_ALIASED_ENABLED which makes me wonder if work was started. I tried setting that in mapagg.cpp but ran into compile errors and didn’t try and track those down.

Of course you’d have to live with 1 pixel wide lines…

Steve

From: Erik H [mailto:erik.h11.01 at gmail.com<mailto:erik.h11.01 at gmail.com>]
Sent: Monday, October 16, 2017 1:15 PM
To: Lime, Steve D (MNIT) <steve.lime at state.mn.us<mailto:steve.lime at state.mn.us>>
Cc: mapserver-users at lists.osgeo.org<mailto:mapserver-users at lists.osgeo.org>
Subject: Re: [mapserver-users] Draw roads WITHOUT anti-aliasing

Thanks for your reply, but I should have mentioned that I have a LOT of different colors to be displayed, almost a million...

I should also have mentioned that I've already tried to filter out the anti-aliased pixels by setting all alpha bytes to 255 and then assuming that all pixels that don't have alpha=255 in the PNG can be removed, but that assumption seems to be wrong.

On Mon, Oct 16, 2017 at 2:00 PM, Lime, Steve D (MNIT) <steve.lime at state.mn.us<mailto:steve.lime at state.mn.us>> wrote:
Hmmm… I wonder if you just could use a pre-computed palette to control quantizing to 8 bits. You can supply a palette file (RGB or RGBA) and the MapServer will map 24/32-bit values to those in the palette. Format options are:

     FORMATOPTION "PALETTE_FORCE=TRUE"
    FORMATOPTION "PALETTE=palette.txt"

This will definitely limit the colors in your output image to those you specify. The question is whether or not the anti-aliased colors will map to the right color and that will depend on your palette. I did write a simple test with a 5 color palette (black, white, red, green and blue) and it seems to work ok but that’s a very simple palette… Based on your application it might work though.

-          http://maps1.dnr.state.mn.us/cgi-bin/mapserv70?map=/usr/local/mapserver/apps/test/palette/test.map&mode=map (24-bit)
-          http://maps1.dnr.state.mn.us/cgi-bin/mapserv70?map=/usr/local/mapserver/apps/test/palette/test.map&mode=map&map.imagetype=png8 (8-bit w/5 colors)

Steve

From: mapserver-users [mailto:mapserver-users-bounces at lists.osgeo.org<mailto:mapserver-users-bounces at lists.osgeo.org>] On Behalf Of Erik H
Sent: Monday, October 16, 2017 10:58 AM
To: mapserver-users at lists.osgeo.org<mailto:mapserver-users at lists.osgeo.org>
Subject: [mapserver-users] Draw roads WITHOUT anti-aliasing

I'm running a tiling server that uses MapServer 7.0.4 to generate PNGs.

My colleagues came up with an ingenious idea to animate traffic conditions that would require them to identify road segments based on their color. They asked me to generate tiles with a predetermined RGBA value per road segment.

I configured a layer of type LINE, with a STYLE section containing 'COLOR [palette]' (palette being a field in the database query). Initially, I thought I was creating the images my colleagues needed, but it seems that the anti-aliasing causes some pixels to have colors other than the one I specified; this prevents us from identifying the road segments.

We can live without anti-aliasing, but I was unable to turn it off; I tried both the AGG/PNG and GD/PNG drivers and messed with various FORMATOPTION identifiers, but nothing seemed to make any difference.

Any suggestions?

Thanks.