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Fri Aug 1 21:40:07 2014

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QGIS Planet

HTML map tips in QGIS

New fresh QGIS feature! So fresh in fact you can still smell the wet paint :)

QGIS (development build) can now display map tips using HTML (a subset anyway).

To enable the new map tips: Open the Layer Properties dialog for a layer and select the Display tab

Display tab to set HTML map tips

In action

Layer properties for HTML map tip

Notice how we can also use a QGIS expression. Anything inside [% %] will be evaluated and replaced with the value in real-time. We can even use a CASE statement. Pretty cool!

And the result when hovering over a feature

HTML in QGIS map tip? Yes! WOOT!

Hold on. Pause the track! We can even use some CSS to make it more fancy.


<style>
h1 {color:red;}
p.question {color:blue;}
</style>
<h1> [% "NAME" %] </h1>
<br>
<img src="[% "image" %]" />
<br>
<p class="question">Is this place a country?</p>
<br>
[% CASE WHEN "TYPE" = 'Country' THEN 'Yes' ELSE 'No. It is a ' || "TYPE" END %]

CSS in a html map tip

Happy Mapping :)


Filed under: Open Source, qgis Tagged: FOSSGIS, gis, mapping, Open Source, qgis, styling, tips

Generating chainage (distance) nodes in QGIS

Something that I need to do now and then is generate points along a line at supplied distance.  I had never really looked into doing it in QGIS until this question poped up on gis.stackexchange.com.  This is a quick blog post because I thought it was a pretty handy little thing to do.

In the development version there is a new method on QgsGeometry called interpolate. This method takes a distance and returns a point along a line at that distance. Perfect! We can then just wrap this in a loop and generate a point increasing the distance as we move along

from qgis.core import (QgsFeature, QgsGeometry,
                       QgsVectorLayer, QgsMapLayerRegistry,
                       QgsField)
from PyQt4.QtCore import QVariant
from qgis.utils import iface

def createPointsAt(distance, geom):
    length = geom.length()
    currentdistance = distance
    feats = []

    while currentdistance < length:
        # Get a point along the line at the current distance
        point = geom.interpolate(currentdistance)
        # Create a new QgsFeature and assign it the new geometry
        fet = QgsFeature()
        fet.setAttributeMap( { 0 : currentdistance } )
        fet.setGeometry(point)
        feats.append(fet)
        # Increase the distance
        currentdistance = currentdistance + distance

    return feats

def pointsAlongLine(distance):
    # Create a new memory layer and add a distance attribute
    vl = QgsVectorLayer("Point", "distance nodes", "memory")
    pr = vl.dataProvider()
    pr.addAttributes( [ QgsField("distance", QVariant.Int) ] )
    layer = iface.mapCanvas().currentLayer()
    # Loop though all the selected features
    for feature in layer.selectedFeatures():
        geom = feature.geometry()
        features = createPointsAt(distance, geom)
        pr.addFeatures(features)
        vl.updateExtents()

    QgsMapLayerRegistry.instance().addMapLayer(vl)

The above code might look a bit scary at first if you have never done any Python/pyqgis but hopefully the comments will ease the pain a little. The main bit is the createPointsAt function.

Cool! If we want to use this we can just stick it in a file in the .qgis/python folder (lets call it pointtools.py) and then run import pointtools in the python console.

So lets have a go. First select some objects then run the following in the Python Console

import pointtools
pointtools.pointsAlongLine(40)

That will generate a point every 40 meters along then selected lines

Distance nodes along line in qgis-dev

To generate nodes along different lines, select the new features, then call pointtools.pointsAlongLine(40) in the Python console.

Simple as that!

(Who knows, someone (maybe me) might even add this as a core object function in QGIS in the future)


Filed under: Open Source, qgis Tagged: language python, Open Source, osgeo, pyqgis, python, qgis, qgis-tips, Quantum GIS, tips

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