3

I have a polygon geometry and I have some points that are its vertices. QGIS 2.18 changes randomly the position of labels. When I choose 'outside of symbol' option, labels are showed outside of point symbol, but not outside of polygon.

enter image description here

I am doing many maps and I need labels to be showed like this.

enter image description here

How could I show labels of these points changing its position to be outside of the polygon automatically?

Is there any rule based solution or anything else?

6

I propose the following way

  1. Add field 'type' to your point table.
  2. Fill values of this field with the values 0 (above left point), 2 (above right point), 8 (below right point), 6 (below left point).
  3. In dialog layers properties select Labels and Rule-Based labeling. Labeling
  4. Press Add rule (down part of the dialog in form of a plus sign).
  5. Fill the field 'Label with' with the name of your table field (id in my case).
  6. Press the item Placement -> Quadrant -> Field type...-> Type Placement
  7. Set Distance (1 in millimeter)
  8. After applying those properties you get the following picture Labels

  9. In order to make placement of your labels automatically, you should add an action to the layer that contains polygons. That can be done by choosing Actions item of Layer properties.

Add action

  1. Press Plus button to evoke Edit action dialog. Edit action

  2. Fill the proposed elements as in the picture and place the following code in the action text box

import math

def label_placement(bear):
    place = 0
    if bear < 22.5 or bear > 337.5:
        place = 0
    elif bear >= 22.5 and bear < 67.5:
        place = 2
    elif bear >= 67.5 and bear < 112.5:
        place = 5
    elif bear >= 112.5 and bear < 157.5:
        place = 8
    elif bear >= 157.5 and bear < 202.5:
        place = 7
    elif bear >= 202.5 and bear < 247.5:
        place = 6
    elif bear >= 247.5 and bear < 292.5:
        place = 3
    elif bear >= 292.5 and bear <= 337.5:
        place = 0

    return place


def reverse_azimuth(az):
    if az < 180:
        az += 180
    else:
        az -= 180
    return az


def direct_geodetic_task(pnt, dist, bear):
    deg = bear * math.pi / 180
    dx = dist * math.sin(deg)
    dy = dist * math.cos(deg)
    x = pnt.x() + dx
    y = pnt.y() + dy
    return QgsPoint(x, y)


def point_in_poly(x, y, poly):
    n = len(poly)
    inside = False
    p1x = poly[0].x()
    p1y = poly[0].y()
    for i in range(n + 1):
        p2x = poly[i % n].x()
        p2y = poly[i % n].y()
        if y > min(p1y, p2y):
            if y <= max(p1y, p2y):
                if x <= max(p1x, p2x):
                    if p1y != p2y:
                        xints = (y - p1y) * (p2x - p1x) / (p2y - p1y) + p1x
                    if p1x == p2x or x <= xints:
                        inside = not inside
        p1x, p1y = p2x, p2y
    return inside


def clear_layer(layer):
    listOfIds = [feat.id() for feat in layer.getFeatures()]
    layer.dataProvider().deleteFeatures(listOfIds)


def bisextrix_bearing(H, A, T):
    x0 = (H.x() + T.x()) / 2
    y0 = (H.y() + T.y()) / 2

    azAH = A.azimuth(H)
    azAT = A.azimuth(T)
    return (azAH + azAT) / 2.0


print "Ok"
layer = None
rectLayer = None
layerList = QgsMapLayerRegistry.instance().mapLayersByName("as")
if len(layerList) > 0:
    layer = layerList[0]
else:
    print "Point table not found"

layerList = QgsMapLayerRegistry.instance().mapLayersByName("planilha")
if len(layerList) > 0:
    rectLayer = layerList[0]
else:
    print "Polygon table not found"

print layer.name()
print rectLayer.name()

# clear_layer(layer)

counter = 0
for feat in rectLayer.getFeatures():
    polys = feat.geometry().asPolygon()

    poly = polys[0]
    if len(poly) > 3:
        print counter, "Vertices=", len(poly)
        poly_len = len(poly)
        for i in range(0, poly_len - 1):
            first_ind = i - 1
            if first_ind < 0:
                first_ind = poly_len - 2
            cr0 = poly[first_ind]
            cr1 = poly[i]
            cr2 = poly[i + 1]

            counter += 1
            az = bisextrix_bearing(cr0, cr1, cr2)
            if az < 0:
                az = 360 + az

            pnt1 = direct_geodetic_task(cr1, 1, az)
            res = point_in_poly(pnt1.x(), pnt1.y(), poly)
            if res:
                az = reverse_azimuth(az)
            type = label_placement(az)

            tolerance = 10
            searchRect = QgsRectangle(pnt1.x() - tolerance,
                                      pnt1.y() - tolerance,
                                      pnt1.x() + tolerance,
                                      pnt1.y() + tolerance)
            request = QgsFeatureRequest()
            request.setFilterRect(searchRect)
            cnt = 0
            for ftr in layer.getFeatures(request):
                cnt += 1
                ftr.setAttribute("type", type)
                layer.updateFeature(ftr)

            # In case no features found in the vicinity of the vertex a point feature will be generated
            if cnt == 0:
                feat = QgsFeature(layer.pendingFields())
                feat.setAttribute("id", counter)
                feat.setAttribute("label", 'X-' + str(counter))
                feat.setAttribute("type", type)
                feat.setGeometry(QgsGeometry.fromPoint(QgsPoint(cr1.x(), cr1.y())))
                (res, outFeats) = layer.dataProvider().addFeatures([feat])

layer.triggerRepaint()
  1. In fact, the python code is included as part of the project that can be found by the GitHub link https://github.com/ulabnit07/12 You can find a Qgis project example.qgs and all the rest files.

    1. After opening example.qgs you can try to launch the action Generate points on the layer rectangle that performs the desired function. Result

Do not hesitate to ask if anything unclear from what I explained.

  • It is very helpful and a good solution for few geometries, but I have about 300 geometries to put these numbers at attribute table. Is there a not manually way to put them? An expression that defines their position related to polygon? Unfortunately I am not finding a solution. – Carolina Dec 26 '18 at 12:20
  • Actually, I can't see the possibility to build such an expression inside Edit rule dialog. But we can generate point features of some layer with a value of the mentioned field 'type' and then assign the qml style to this point layer. After that the proper position of the labels guaranteed. This way can be done with some specific python code. Are all of your rectangle geometries included in one layer? – Vadym Dec 26 '18 at 13:15
  • Yes, they are all included in one layer, but they are not all rectangles. Most of them have irregular shape. – Carolina Dec 27 '18 at 1:42
  • Your last edition worked exactly as I need. Thank you very much! I just have to understand your code to change the part that it clears all the attribute table of the point layer and it just leaves 'id' and 'type' data, because I already have a column with label and another with important data. Does it seem complicated to do? – Carolina Jan 1 at 16:30
  • 1
    I've changed the python code. The better way to use the modified code is to download files from the GitHub link github.com/ulabnit07/12 – Vadym Jan 2 at 11:07

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.