Re: Home Range Plugin - Projection and map units

[Damiano G. Preatoni]

In un messaggio del Friday 18 September 2009, Max Ringler ha scritto:

> Are there any known issues with projections and/or map units and the home
> range plugin?
>
> When running MCP and kernel analyses, the original point coordinates of my
> data seem to get rounded to the next lower meters (decimal digits are
> discarded). Accordingly the MCP shapes are "somewhat" correct in shape, but
> positioned way off the orignal points - same for kernels.
>
> My project has meters as map unit and the projects and shapefiles
> projection is +proj=utm +zone=22 +ellps=WGS84 +datum=WGS84 +units=m
> +no_defs.
>

AFAIK (Clement, any feedback?), since the home range plugin uses adehabitat as
backend, there should be no issues both with projection (adehabitat is
somewhat of "projection-agnostic") and "decimals".

Keep in mind that, since you're working with a metric CRS (i.e. UTM zone 22)
the figures are in meters, and the "decimals" you're losing are in fact
_centimeters_, and normally (either with VHF or GPS) a spatial resolution
level at the tenth of meters is normally accepted.
Such a precision (down to the centimeter) should be necessary if you're
working on small species (insects? shrews?), but normally one doesn't look at
decimals in a metric CRS...

About the "way off" effect... I smell datum shift problems. Are you
visualizing the results in some GIS that handles projection poorly or there is
some flaw in how you specify your CRS?


Hope this Helps


--
  Cum tacent, clamant. When they are silent, they shout. -Cicero
-----------------------------------------------------------
Damiano G. Preatoni, PhD

Unità di Analisi e Gestione delle Risorse Ambientali
Dipartimento Ambiente-Salute-Sicurezza
Università degli Studi dell'Insubria
Via J.H. Dunant, 3 - 21100 Varese (ITALY)

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