Re: Plant mapping

Michael Hasemann (jmh@ele.vtt.fi)
Fri, 8 Mar 1996 08:37:30 +0200 (EET)

Hi Rick,

just a few comments.

>
> I tried to make it clear that the circle locations would be "snapped" to
> a coarse grid. This means that if the location was 1023.25 km North of
> the equator, then we would actually display the latitude as 1020 km
> (snapped to a 10km grid) or 1000 km (snapped to a 100 km grid). This
> builds in an uncertainty in the area equal to the square of the
> grid spacing.

I think we should adapt a standard here and various levels of dilution/
grid coarseness could be employed if wanted as well. The grid I am
proposing is the UTM grid based on the WGS84 geoid/datum.

Coarseness can be realized by leaving the less significant digits of
the UTM datum blank. Formulas to convert from lat/lon to UTM/WGS84
back and forth are readily available.

>
> This means that the WEB maps do not show information centered on "exact
> longitude and latitude". We do not give away precise information no
> matter how small we make the circles.
>
> Practically, this will occur automatically. In a 3"x5" GIF bitmap
> of north america, any data is only accurate only to the resolution of a
> bitmap pixel. Simply by limiting the zoom factor on the map generator,
> it is easy to control how much information is displayed.

Sure, if you have/want such maps but what if you want to go really
beyond the resolution of the map. I think the better way is to seperate
location information (as precise as wanted) from the actual maps. A
simple drawing algorithm (if wanted) can be used to display location
information on the map.

>
> Practically speaking, most people would simply not want to wait for
> a world map, accurate to 100 meters, to download.
>

But perhaps location data as precise as 100m.

>
> If experience shows that the information is not being mis-used, then we
> certainly have the option of releasing the full accuracy textual database
> later on. The limited resolution display is simply a compromise so that
> we can go ahead without risking the plant populations. We will be able
> to reassess this policy at any time.
>

Again keeping location information seperate from the maps makes above
much easier.

> Best regards,
> --
> Rick Walker
>

..Michael

-- 
  Michael Hasemann | Technical Research Centre of Finland - Automation
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