The Geoserver Explorer plugin for QGis ( 2): limitations

Continuing the following article: The Geoserver
Explorer plugin QGis (1) installation and configuration, we will discuss
the
limitations of the plugin.

Limitations of the plugin

Here is a list
of limitations and problems likely
to come up.

Limitations related to the SRC.
GeoServer
can
experience
problems when a custom SRC system
is
being used by QGIS. The SRC definition that works
correctly
when
rendering the QGIS layer, may not work when importing the layer
to
GeoServer
. Usually this results in a layer
that is published but that does not have a SRC set
and it is not activated. You can correct
it
manually
by
selecting
the layer in the Explorer tree
and
amending
its CRS.

Note that the layers are imported
by
using
the SRC defined in the original data source
(i.e.,
the file prj if you
use
a
shapefile).
Defining
a different SRC by using the option Set Layer CRS
in
the QGIS table of contents will not have any effect when
importing the layer to GeoServer , except
if
you
save
the layer with this SRC so that the SRC definition is stored
with the data layer.

Limitations related to the
layers names.
GeoServer
Explorer uses the GeoServer REST API to get the list of layers in the catalogue.
The REST API describes the layers without working space,
which means that if you have
two
layers with the same name and in different workspaces
(for example , ws1: macouche and ws2: macouche ),
they will be displayed just
as one ( macouche in this
case
).

When this is the case, the
situation is ambiguous and GeoServer
Explorer cannot differentiate the layers depicting the same name but
belonging
to different workspaces. The layer, as described by the
REST API, is added to the explorer tree,
but it represents only one of several layers that share the
same name. To denote this special situation, the layer is
displayed
with a warning icon, and a warning message appears
in
the layer description.

Style limitations

Another important
limitation is due to the different
versions of the SLD supported by QGIS and GeoServer .
The
GeoServer explorer
allows to edit the style of a
layer
GeoServer
directly
from the QGIS interface. It can
convert
a defined QGIS style into a downloaded from the GeoServer
catalogue and use GeoServer styles for the QGIS layers. This
two-way conversion is, however,
limited.
This is, mainly, due
to the different versions of SLD supported by QGIS and GeoServer , as well as
to
some
GeoServer and QGIS limitations. SLD is in use
as
a common format by GeoServer Explorer to describe the styles in the QGIS and
GeoServer layers, but some incompatibilities
exist. To increase the compatibility between them, specific
routines have been added
to the explorer GeoServer . However,
in some case, a defined style
in
QGIS may not be compatible with the elements supported
by GeoServer explorer , and the publication of a layer
will be executed with a modified style , or even
by
using
a default style.

This problem exists even
when
using the latest version of GeoServer, but older versions of GeoServer
can
present
more incompatibilities and do not validate
a
great
part
of the SLD produced by the GeoServer explorer.

As a general rule, the basic style
for vector layers should operate
without problems in both ways,
but a more complex symbology
will
be
partially
or
completely
inconsistent, leading to differences between, for example, the style you
set
in
QGIS and the style that the GeoServer layer will depict. Raster
layers have a more limited support.

Incidentally, I had to set a style for a QGis project and
load it into Geoserver with the plugin.
The style was correct for GeoServer (what
can be double checked with the option Layers Preview). But when
we tried to reload the layer into QGis, the style was not accepted
by QGis…

Here is a list
of acknowledged limitations for the LTC management:

Raster layers

The raster style is taken in
charge only from QGIS towards GeoServer . It
means
that
a raster style can be created
by
using
the
QGIS user interface and downloaded towards GeoServer,
but a raster style from GeoServer cannot be used
for a QGIS layer . When a GeoServer
layer
is added to an ongoing QGIS project with the assistance of GeoServer Explorer,
its symbology will be used only
 if it is
a
vector
layer, but will be ignored in the case of a
raster
layer and the default QGIS style will be used .
Only
pseudo colour Single Band Gray and
Singleband are used.
In
this
latter
case,
the correct colour interpolation is not supported, but the
modes Linear and Discrete are employed.

The use of the plugin is a
very interesting alternative in relation to the classic
loading process of a
 Geoserver style .

Vector layers

When converting a GeoServer style into
a
QGIS style, the style is always defined
as
a style based on rules. This means
that even if the style is created using a different
type, such as graduated when it is downloaded into
a GeoServer catalogue and re-modified from QGIS it
will
not appear as a Graduate style. This is due to the way QGIS includes
the LTC styles, by, always, interpreting always as
a
Rule-based
type symbology.
Basic
labelling is employed, but all
labels (labels) will not be exported QGIS to LTC and downloaded GeoServer.
In
particular,
the advanced labelling is dependent on the
data is not used.
Importing
a
points
layer with a QGIS SVG style towards Geoserver generates
a
WMS
layer that respects this SVG symbol.
The same is not supported for the time being if the layer is
reimported
as
a WFS layer .

In the next article we will discuss how to use the Geoserver
Explorer plugin .

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