Re: [QGIS-Developer] cannot import processing algorithm in 3.6
Hi all On Mon, Apr 1, 2019 at 1:16 PM Raymond Nijssen wrote: > > Last HF martin and I discussed the current geometry model and some of > the flaws and weird things. Especially the set() and get() are not very > logical function names to me. Just to add more thoughts to this... There is obviously a lot of confusion regarding geometry API in QGIS since the big refactoring. Things like QgsGeometry vs QgsAbstractGeometry ... or QgsPoint vs QgsPointXY. I would say some bits are fixable without too much effort (e.g. add some missing convenience constructors), but most bits will need to wait until QGIS 4.0 (e.g. getting rid of methods accepting/returning QgsPointXY within geometry API). One idea that I wanted to explore is whether we could avoid having QgsGeometry in the Python API at all, so it would be a mapped type like QVariant is in PyQt5. So for example, feat.geometry() would return directly QgsPoint or QgsLineString. This would avoid the need to extract the internal geometry object from QgsGeometry and vice versa (wrap internal geometry object into QgsGeometry). I have not tried it in practice yet though and it will definitely be an API break, but if it works, it should simplify things a lot :-) Cheers Martin ___ QGIS-Developer mailing list QGIS-Developer@lists.osgeo.org List info: https://lists.osgeo.org/mailman/listinfo/qgis-developer Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-developer
Re: [QGIS-Developer] cannot import processing algorithm in 3.6
Thank you Nyall!
Sorry for replying so late but I suddenly went on a busy 2 week trip abroad.
Last HF martin and I discussed the current geometry model and some of
the flaws and weird things. Especially the set() and get() are not very
logical function names to me.
To find out about the model I tested it using a script in the qgis
python console. I'm still using it often to figure how to create and
convert geometries. Hope it helps others as well. Would be nice for the
cookbook maybe.
Kind regards,
Raymond
#points
p1 = QgsGeometry().fromWkt('point(0 0)')
print(p1) #
print(p1.asPoint()) #
print(p1.centroid()) #
print(p1.buffer(1, 1)) # 0))>
print(p1.get()) #
p2 = QgsPoint(1,2)
print(p2) #
p2g = QgsGeometry(p2)
print(p2g) #
print(p2) #
print(p2.centroid()) #
print(QgsPointXY(p2.x(), p2.y())) #
#print(QgsGeometry(p2)) #!!! Converts
p2 in place ? !!!
g = QgsGeometry()
print(g)
g.set(p2)
print(g)
p3 = QgsPointXY(2, 0)
print(p3) #
print(QgsGeometry.fromPointXY(p3)) #
print(QgsPoint(p3.x(), p3.y())) #
# lines
l1 = QgsGeometry().fromWkt('linestring((0 0, 1 1, 1 2))')
print(l1) #
print(l1.buffer(1, 1).asPolygon())
print(l1.asPolyline()) # [, 1)>, ]
#print(QgsLineString(l1.asPolyline())) # TypeError: index 0 has type
'QgsPointXY' but 'QgsPoint' is expected
p1 = QgsPointXY(100,100)
print(p1)
p2 = QgsPoint(200,200)
l1 = QgsLineString()
print(l1)
l1.addVertex(QgsPoint(p1.x(), p1.y()))
l1.addVertex(p2)
print(l1)
pg1 = QgsGeometry().fromWkt('polygon((0 0, 0 1, 1 1, 1 0, 0 0))')
print(pg1) #
pg2 = pg1.get()
print(pg2) #
g = QgsGeometry()
g.set(pg2)
print(g) #
On 21-03-19 09:43, Nyall Dawson wrote:
On Thu, 21 Mar 2019 at 15:59, Raymond Nijssen wrote:
def toLines(geom):
return QgsGeometry(geom.get().boundary())
(Using
https://qgis.org/pyqgis/master/core/QgsAbstractGeometry.html#qgis.core.QgsAbstractGeometry.boundary
)
Nyall
Thanks Nyall, that works!
Great, thanks for the confirmation. And because I've got to do mapping
all day, I'm in a good mood, and you get a free PyQGIS lesson:
geom.get() : gives you the underlying fundamental geometry object
attached to the feature. QgsFeature.geometry() returns a QgsGeometry
object, which is more or less a "container" for geometries. It's got
some convenient methods which apply to ALL geometry types, but
sometimes you need to dig down to the actual geometry primitive. In
that case you use geometry.get(), and you get the fundamental
QgsPoint/QgsLineString/QgsPolygon/etc object. It's actually generally
preferable to call "geometry.constGet()", IF you are doing some
operation which doesn't alter the geometry in place (like you are
here). But that's a complex microoptimisation.
geom.get().boundary() gives you the topological boundary of the
primitive. For polygons this is their exterior + interior rings, for
lines it's their start and end point (unless it's a closed ring, in
which case you get a null geometry). Points have no boundary. Using
boundary() to convert polygons to lines is the most efficient method -
it's very heavily optimised, and works perfectly with curved geometry
types and maintains any Z or M values which may be present.
Lastly, you need to wrap the result back up into a QgsGeometry object
- hence QgsGeometry(boundary() ). This is because most of QGIS API
works with QgsGeometry objects (remember, they are like "containers"
holding a geometry), and NOT the fundamental geometry objects.
Done! A super-efficient, rock solid approach which will work with all
input geometry types. Win!
(for reference - this is what the polygons to lines algorithm actually
does in the background too)
Nyall
I will try tomorrow.
One last question, it seems to me like the old code is working again in
3.7. Can you confirm that?
Shouldn't be -- maybe you have a leftover .py file here?
Indeed. I did a clean install and it is not working in my 3.7 anymore.
Regards,
Raymond
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Re: [QGIS-Developer] cannot import processing algorithm in 3.6
On Thu, 21 Mar 2019 at 15:59, Raymond Nijssen wrote: > > > > def toLines(geom): > > return QgsGeometry(geom.get().boundary()) > > > > (Using > > https://qgis.org/pyqgis/master/core/QgsAbstractGeometry.html#qgis.core.QgsAbstractGeometry.boundary > > ) > > > > Nyall > > Thanks Nyall, that works! Great, thanks for the confirmation. And because I've got to do mapping all day, I'm in a good mood, and you get a free PyQGIS lesson: geom.get() : gives you the underlying fundamental geometry object attached to the feature. QgsFeature.geometry() returns a QgsGeometry object, which is more or less a "container" for geometries. It's got some convenient methods which apply to ALL geometry types, but sometimes you need to dig down to the actual geometry primitive. In that case you use geometry.get(), and you get the fundamental QgsPoint/QgsLineString/QgsPolygon/etc object. It's actually generally preferable to call "geometry.constGet()", IF you are doing some operation which doesn't alter the geometry in place (like you are here). But that's a complex microoptimisation. geom.get().boundary() gives you the topological boundary of the primitive. For polygons this is their exterior + interior rings, for lines it's their start and end point (unless it's a closed ring, in which case you get a null geometry). Points have no boundary. Using boundary() to convert polygons to lines is the most efficient method - it's very heavily optimised, and works perfectly with curved geometry types and maintains any Z or M values which may be present. Lastly, you need to wrap the result back up into a QgsGeometry object - hence QgsGeometry(boundary() ). This is because most of QGIS API works with QgsGeometry objects (remember, they are like "containers" holding a geometry), and NOT the fundamental geometry objects. Done! A super-efficient, rock solid approach which will work with all input geometry types. Win! (for reference - this is what the polygons to lines algorithm actually does in the background too) Nyall > > > > > > >> > >> I will try tomorrow. > >> > >> One last question, it seems to me like the old code is working again in > >> 3.7. Can you confirm that? > > > > Shouldn't be -- maybe you have a leftover .py file here? > > Indeed. I did a clean install and it is not working in my 3.7 anymore. > > > Regards, > Raymond ___ QGIS-Developer mailing list QGIS-Developer@lists.osgeo.org List info: https://lists.osgeo.org/mailman/listinfo/qgis-developer Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-developer
Re: [QGIS-Developer] cannot import processing algorithm in 3.6
def toLines(geom): return QgsGeometry(geom.get().boundary()) (Using https://qgis.org/pyqgis/master/core/QgsAbstractGeometry.html#qgis.core.QgsAbstractGeometry.boundary ) Nyall Thanks Nyall, that works! I will try tomorrow. One last question, it seems to me like the old code is working again in 3.7. Can you confirm that? Shouldn't be -- maybe you have a leftover .py file here? Indeed. I did a clean install and it is not working in my 3.7 anymore. Regards, Raymond ___ QGIS-Developer mailing list QGIS-Developer@lists.osgeo.org List info: https://lists.osgeo.org/mailman/listinfo/qgis-developer Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-developer
Re: [QGIS-Developer] cannot import processing algorithm in 3.6
On Thu, 21 Mar 2019 at 12:17, Raymond Nijssen wrote: > > Hi Nyall, thanks for your answer. > > Somewhere in the middle of a calculation process (not an algorithm) I'd > like to add a polygon feature to a line layer. I'm using the function to > turn the polygon into a line geometry. > > > > I'm using it like this and don't know I figured this out or decided on it: > > from processing.algs.qgis import PolygonsToLines > > toLines = PolygonsToLines.PolygonsToLines().convertToLines > > > then later on many places in my code: > > geom = toLines(geom) > > > > I remember it took me a while to figure out that second line, but having > my own short "alias" function toLines() is very convenient. But maybe I > can create it in another way, holding the processing.run code. I'd replace this with: def toLines(geom): return QgsGeometry(geom.get().boundary()) (Using https://qgis.org/pyqgis/master/core/QgsAbstractGeometry.html#qgis.core.QgsAbstractGeometry.boundary ) Nyall > > I will try tomorrow. > > One last question, it seems to me like the old code is working again in > 3.7. Can you confirm that? Shouldn't be -- maybe you have a leftover .py file here? > > Kind regards, > Raymond > > > > On 21-03-19 01:34, Nyall Dawson wrote: > > On Thu, 21 Mar 2019 at 02:40, Raymond Nijssen wrote: > >> > >> The folowing line works for me in 3.4.3 and 3.7 (built today) but not in > >> 3.6.0 > >> > >> from processing.algs.qgis import PolygonsToLines > > > > It was ported from Python -> c++, so is no longer importable like > > this. What's your use case for importing direct rather than running > > via processing.run? > > > > Nyall > > > > -- > Terglobo > Fahrenheitstraat 1 > 5223 BJ 's-Hertogenbosch > The Netherlands > +31 (0) 6 25 31 49 83 ___ QGIS-Developer mailing list QGIS-Developer@lists.osgeo.org List info: https://lists.osgeo.org/mailman/listinfo/qgis-developer Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-developer
Re: [QGIS-Developer] cannot import processing algorithm in 3.6
Hi Nyall, thanks for your answer. Somewhere in the middle of a calculation process (not an algorithm) I'd like to add a polygon feature to a line layer. I'm using the function to turn the polygon into a line geometry. I'm using it like this and don't know I figured this out or decided on it: from processing.algs.qgis import PolygonsToLines toLines = PolygonsToLines.PolygonsToLines().convertToLines then later on many places in my code: geom = toLines(geom) I remember it took me a while to figure out that second line, but having my own short "alias" function toLines() is very convenient. But maybe I can create it in another way, holding the processing.run code. I will try tomorrow. One last question, it seems to me like the old code is working again in 3.7. Can you confirm that? Kind regards, Raymond On 21-03-19 01:34, Nyall Dawson wrote: On Thu, 21 Mar 2019 at 02:40, Raymond Nijssen wrote: The folowing line works for me in 3.4.3 and 3.7 (built today) but not in 3.6.0 from processing.algs.qgis import PolygonsToLines It was ported from Python -> c++, so is no longer importable like this. What's your use case for importing direct rather than running via processing.run? Nyall -- Terglobo Fahrenheitstraat 1 5223 BJ 's-Hertogenbosch The Netherlands +31 (0) 6 25 31 49 83 ___ QGIS-Developer mailing list QGIS-Developer@lists.osgeo.org List info: https://lists.osgeo.org/mailman/listinfo/qgis-developer Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-developer
Re: [QGIS-Developer] cannot import processing algorithm in 3.6
On Thu, 21 Mar 2019 at 02:40, Raymond Nijssen wrote: > > The folowing line works for me in 3.4.3 and 3.7 (built today) but not in > 3.6.0 > > from processing.algs.qgis import PolygonsToLines It was ported from Python -> c++, so is no longer importable like this. What's your use case for importing direct rather than running via processing.run? Nyall ___ QGIS-Developer mailing list QGIS-Developer@lists.osgeo.org List info: https://lists.osgeo.org/mailman/listinfo/qgis-developer Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-developer
[QGIS-Developer] cannot import processing algorithm in 3.6
The folowing line works for me in 3.4.3 and 3.7 (built today) but not in 3.6.0 from processing.algs.qgis import PolygonsToLines Could anyone test in the python console and confirm? Thanks! Raymond -- Terglobo Fahrenheitstraat 1 5223 BJ 's-Hertogenbosch The Netherlands +31 (0) 6 25 31 49 83 ___ QGIS-Developer mailing list QGIS-Developer@lists.osgeo.org List info: https://lists.osgeo.org/mailman/listinfo/qgis-developer Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-developer
