[GRASSLIST:5079] Re: ps.map and PNG driver comparison

[Miha Staut]

 --- Hamish <hamish_nospam at yahoo.com> wrote: 
> > Why do raster layers printed with ps.map look more
> > coarse (lower resolution) than ones printed with
> PNG
> > driver?
> 
> 
> The number of raster cells used in a ps.map map is
> exactly the same as
> the number defined by rows and columns in the
> g.region settings.
> Make sure you have the resolution correct before
> creating the map.

I did that.

> The number of cells used by the PNG driver will be
> resampled to fit in
> the monitor height and width, after the region
> resolution resampling.

I set the environment variables GRASS_WIDTH and
GRASS_HEIGHT to match the g.region -p output, so the
PNG file should have exactly the same number of rows
and columns as ps.map output. But even printed to
paper (same size) the maps in detail look different.
The postscript file looks more "edgy" while the png
file looks smoother. I tried to print some
topographical maps with generaly rasterized line data.

Thanks for the reply, Miha Staut


> So theoretically the ps.map output should generally
> be higher resolution
> than the PNG output.. usually you can lower the
> region's resolution
> before running ps.map and still get high quality
> output from a much
> smaller file. Otherwise you get 40mb postscript
> files...
> 
> But a printed page will have finer detail than your
> monitor. Standard
> PostScript/PDF is 72 dpi but a fine raster might
> print at 300 dpi.
> Your monitor (PNG driver output) will generally by
> only ca. 800 pixels
> wide, ie the same as a 2.7 inch printed version.
> Expand that to a full
> printed page and you apparenlty lower resolution ??
> 
> Hamish


	
	
		
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