Hi,
I'd like to hear what people think about the idea of adding a new
custom EPSG code, EPSG:0, to GeoServer, to be used when no EPSG code can be
guessed from the data source (or when it's just plain missing).
EPSG:0 would map to DefaultEngineeringCRS.GENERIC_2D, which is designed to be
a lenient wildcard CRS, from the javadoc:
----------------
A two-dimensional wildcard coordinate system with x, y axis in metres.
At the difference of CARTESIAN_2D, this coordinate system is treated
specially by the
default coordinate operation factory with loose transformation rules:
if no transformation
path were found (for example through a derived CRS), then the
transformation from this
CRS to any CRS with a compatible number of dimensions is assumed to be the
identity transform. This CRS is usefull as a kind of wildcard when no
CRS were explicitly specified.
-----------------
The reasoning behind this idea is that way too often people do not
have, or do not know,
the CRS of their data, and are forced to guess with a valid EPSG code.
Maybe the data has no CRS to start with (think abusing GS/OL
to make an high resolution picture browser), maybe it's a building blueprint, or
a town level map made with CAD tools.
Or maybe it's GIS data but you just cannot find anything about the CRS
and you don't
care about reprojection to start with.
So far the common behavior by lots of people has been using EPSG:4326.
However that comes today with too many strings attached to be used as a default
for that case:
- it's geographic, thus it suffers from the axis flipping issue
- it can be wrapped, but the map wrapping heuristics will fail if the
data is not really
within the limits of EPSG:4326 sane values
I guess the drawback for such a code is that it might confuse clients
that try to interpret
the codes (which are normally GIS aware ones).
Another possible for such data might be to pretend it's in a CRS that
is projected,
has a very large (possibly infinite?) ordinate validity range and
includes 0 as valid
value.. something like EPSG:3785 would indeed fit the bill.
The drawback of this one is that it would enable the usage of the reprojection
machinery while it makes no sense to use one.
Opinions?
Cheers
Andrea
--
Ing. Andrea Aime
Technical Lead
GeoSolutions S.A.S.
Via Poggio alle Viti 1187
55054 Massarosa (LU)
Italy
phone: +39 0584962313
fax: +39 0584962313
http://www.geo-solutions.it
http://geo-solutions.blogspot.com/
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