Hello,
I am part of GeoTrellis project where we are creating a Scala wrapper around
JTS. One issue that we have is the treatment of SRID field.
I am hoping to hear from either the developers that made the original design
choice to include SRID field or people using the feature. I would really love
to know what is the design intent behind storing SRID with each geometry and if
it has born out over time.
It seems like SRID is somewhat semantically overloaded. They seem to exist in
either of two states:
1. There is no meaningful value for SRID, or perhaps all the geometries have
the same values. Regardless, all the operations are valid and one writes code
as if SRID field doesn't exist.
2. Geometries must be written somewhere where several SRIDs are possible, for
instance different PostGIS columns. Alternatively geometries are read from some
source with multiple SRID values and the one may want to match SRIDs to ensure
the result of operations on geometries are meaningful.
However in this case the value of SRIDs has to be an index into some undefined
table, possibly EPSG, possible something else. In this way they seem to carry
only some information needed to fully qualify the geometry coordinates.
An alternative design choice might be to construct a tuple with a Geometry and
a CRS object whenever serializing or deserializing geometries. The CRS would
contain all the information to qualify SRID, proj4 code, as well as a name.
This is much heavier than a single integer field but on other hand more
explicit in those cases where SRIDs matter.
Thank you,
--
Eugene Cheipesh
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