[example1] add python implementation

appl/example1/example1.py

+import frackit.geometry as geometry
+
+# we use the unit cube as domain
+box = geometry.Box(0.0, 0.0, 0.0, 1.0, 1.0, 1.0)
+
+# we sample points uniformly within the domain
+from frackit.sampling import makeUniformPointSampler
+pointSampler = makeUniformPointSampler(box)
+
+# returns a sampler from a gaussian distribution with mean and std deviation
+def gaussianSampler(mean, stdDev):
+    import random
+    def sample():
+        return random.gauss(mean, stdDev)
+    return sample
+
+# we sample quadrialeterals within the box with gaussian distributions for the parameters
+from frackit.common import toRadians
+from frackit.sampling import QuadrilateralSampler as QuadSampler
+quadSampler1 = QuadSampler(pointSampler,
+                           gaussianSampler(toRadians(45.0), toRadians(5.0)), # strike angle
+                           gaussianSampler(toRadians(90.0), toRadians(5.0)), # dip angle
+                           gaussianSampler(0.5, 0.1),                        # edge length
+                           0.05)                                             # threshold for minimum edge length
+
+# sampler for quadrilaterals of the secondary orientation
+quadSampler2 = QuadSampler(pointSampler,
+                           gaussianSampler(toRadians(0.0), toRadians(5.0)), # strike angle
+                           gaussianSampler(toRadians(0.0), toRadians(5.0)), # dip angle
+                           gaussianSampler(0.5, 0.1),                       # edge length
+                           0.05)                                            # threshold for minimum edge length
+
+# We want to enforce some constraints on the set of quadrilaterals.
+# In particular, for entities of the same set we want a minimum spacing
+# distance of 5cm, and the quadrilaterals must not intersect in angles
+# less than 30°. Moreover, if they intersect, we don't want intersection
+# edges whose length is smaller than 5cm, and, the intersection should not
+# be too close to the boundary of one of two intersecting quadrilaterals. Here: 5cm.
+from frackit.entitynetwork import EntityNetworkConstraints
+constraintsOnSelf = EntityNetworkConstraints()
+constraintsOnSelf.setMinDistance(0.05)
+constraintsOnSelf.setMinIntersectingAngle(toRadians(30.0))
+constraintsOnSelf.setMinIntersectionMagnitude(0.05)
+constraintsOnSelf.setMinIntersectionDistance(0.05)
+
+# with respect to entities of the other set, we want to have larger intersection angles
+constraintsOnOther = EntityNetworkConstraints()
+constraintsOnOther.setMinDistance(0.05)
+constraintsOnOther.setMinIntersectingAngle(toRadians(40.0));
+constraintsOnOther.setMinIntersectionMagnitude(0.05)
+constraintsOnOther.setMinIntersectionDistance(0.05)
+
+# we use unique identifiers for the entities of the two orientations
+from frackit.common import Id
+idSet1 = Id(1)
+idSet2 = Id(2)
+
+# use the status class to define when to stop sampling
+from frackit.sampling import SamplingStatus
+status = SamplingStatus()
+status.setTargetCount(idSet1, 15) # we want 15 entities in each set
+status.setTargetCount(idSet2, 15) # we want 15 entities in each set
+
+# start sampling into set 1 and keep alternating
+sampleIntoSet1 = True
+
+# lists to store the sampled entities
+entities1 = []
+entities2 = []
+
+print("\n --- Start entity sampling ---\n")
+while not status.finished():
+    # sample a quadrilateral, alternating between sampler 1 and sampler 2
+    quad = quadSampler1.sample() if sampleIntoSet1 else quadSampler2.sample()
+    entitySet = entities1 if sampleIntoSet1 else entities2
+    otherEntitySet = entities2 if sampleIntoSet1 else entities1
+
+    # skip the rest if constraints are violated
+    if not constraintsOnSelf.evaluate(entitySet, quad):
+        status.increaseRejectedCounter()
+        continue
+
+    # skip the rest if constraints are violated
+    if not constraintsOnOther.evaluate(otherEntitySet, quad):
+        status.increaseRejectedCounter()
+        continue
+
+    # the entity is admissible
+    entitySet.append(quad)
+    id = idSet1 if sampleIntoSet1 else idSet2
+    status.increaseCounter(id)
+    status.print()
+
+    # sample into other set the next time
+    sampleIntoSet1 = not sampleIntoSet1
+
+print("\n --- Finished entity sampling ---\n")
+
+# We can now create an entity network from the two sets
+from frackit.entitynetwork import EntityNetworkBuilder
+builder = EntityNetworkBuilder()
+builder.addEntities(entities1);
+builder.addEntities(entities2);
+
+# let the builder construct the network and write it to gmsh file format
+print("\n --- Constructing entity network from the raw entities ---\n")
+network = builder.build();
+
+print("\n --- Writing .geo file ---\n")
+from frackit.io import GmshWriter
+writer = GmshWriter(network);
+writer.write("network", # filename of the .geo files (will add extension .geo automatically)
+             0.1);      # element size to be used
+print("\n --- Finished writing .geo file ---\n")