[GRASS-user] preferred grid size
b.wood at niwa.co.nz
Sun Feb 18 17:55:39 EST 2007
> temiz wrote:
>> is there any preferred grid size for creating topographic index map ?
>> ( elevation map is produced from 1: 25000 scaled topographic map )
> [more of a thought experiment than actual educated advice]
> PostScript points are 1/72", which equates to a thin line on a printed
> page, about as small a feature as is useful in a hardcopy.
I thought Postscript point/line widths vary, depending on the rendering
eg: 300x300, to 2400x2400 etc.... so you can get a 1/2400" line if you
really want it (not that anyone with normal vision could see it :-)
A typical screen resolution (pixel) is around 1/72", so for on screen
viewing these seem reasonable.
It's basically a compromise between scale/clarity & performance, so your
dataset native resolution and extent, intended use, screen only or hard
copy output required, and hardware specs all need to be considered to
devise a suitable grid size for your purpose.
No simple right or wrong answer :-)
> For a 1:25,000 scale, that equates to 347.2" or 8.8m.
> So a raster resolution of 5m would be ok, but it depends on how big that
> makes the data set. A 10000x10000 cell region is probably as big as
> you'd want to go, but a 4000x4000 is much easier to work with so perhaps
> 10m resolution would be a better compromise.
> >From the "How to start with GRASS" help page:
> "The default raster resolution (GRID RESOLUTION) has to be chosen
> according to your needs. Generally, it is advisable to work in steps of
> 0.25 (0.25, 0.5, 1.75, 2.00, 12.25 etc.)."
> I hope I understood and that answers your question,
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