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Given a GPS Log with floating lines within ~5m at a time, is there any process that will automatically clean these and smooth these out?

enter image description here

I have tried Smooth, Simplify, Saga Line Smoothing and Cartographic Line Generalization with various options.

None of these get rid of this level of issues unless settings like the following are used

processing.run("native:smoothgeometry", {'INPUT':'Z:/My Drive/Mangoesmapping/Spatial Projects/2019/020_Adhoc_CAFNECRide/Working/2019_Route_Edit_Master/2019_CAFNEC_MGA94z55.shp|layername=2019_CAFNEC_MGA94z55','ITERATIONS':1,'OFFSET':0.5,'MAX_ANGLE':90,'OUTPUT':'TEMPORARY_OUTPUT'})

But this gets rid of the corners as well and makes the line to smooth.

Ideally I just want all the nodes between the measure tool start/end to be removed automatically and the remaining nodes to be about where the measure line starts/stops.

UPDATE 1

Based on suggestion from @babel I tried Multipart to Singlepart -- > $length --> Select < 0.5 and this does a good job of showing the problem areas.

enter image description here

If I now delete these I get gaps in the data and also some slightly longer slivers left

enter image description here

Dissolving them retains the gaps -is there a way to remove the gaps programmatically.

I've uploaded a dataset to test with at https://drive.google.com/drive/folders/1eaXpIZvUfMhzEtnGmHe9AMgH2ClQBfiX?usp=sharing

  • 1
    I've always fixed those issues by manually removing vertices with the vertex tool. I look forward to finding out a better way. – csk Sep 13 at 17:08
  • 2
    so using the extpression smooth($geometry) did not help? Than maybe have a look here - it's not the same problem, but maybe the approach could be similar: create a buffer around your track and than extract the medial axis: gis.stackexchange.com/questions/319412/… – babel Sep 13 at 20:11
  • This helps me find the issue areas but when you dissolve the lines back there are gaps created where the short lines were deleted. Is there a way to join these programmatically? Will update the question shortly. – GeorgeC Sep 13 at 20:26
  • Try the Join multiple lines plugin. The description says it fills line gaps, although plugins don't always work as described. – csk Sep 16 at 17:34
1

Interesting problem! I have written a python script which I am hoping will do what you are after. The script simplifies line features based on segment length rather than distance between vertices. I have coded a basic ui which allows for selecting the input layer and segment length (which is in the units of the input layer). When you click run, a new temporary layer called 'Simplified line' will be created with the same CRS as the input layer. For each feature in your input layer, all segments longer than the inputted value will be retained, and any gaps will be filled based on the vertices of the retained line segments. If no segments are longer than the inputted value, you will just get new, straight lines from the start and end points of the input features. All fields and attributes are copied from your input layer. I have only tested this on fairly simple data, so it would be great if you would like to try it on your dataset and let me know how it goes. Just paste into an editor in the python console and click run. If it works well, I will likely port it to a processing script.

Example:

(Input layer)

enter image description here

Tool ui:

enter image description here

Result:

enter image description here

class SimplifyLinesDlg(QDialog):
    def __init__(self):
        QDialog.__init__(self)
        self.set_up_ui()

    def set_up_ui(self):
        self.setGeometry(150, 150, 450, 250)
        self.setWindowTitle('Simplify lines by segment length')
        self.cb_label = QLabel('Select input layer:', self)
        self.cb_label.move(25, 30)
        self.layer_cb = QgsMapLayerComboBox(self)
        self.layer_cb.move(125, 25)
        self.layer_cb.resize(300, 20)
        self.layer_cb.setFilters(QgsMapLayerProxyModel.LineLayer)
        self.layer_cb.setShowCrs(True)
        self.label_le = QLabel('Enter segment length (layer units):', self)
        self.label_le.move(25, 105)
        self.length_le = QLineEdit(self)
        self.length_le.move(250, 100)
        self.btn_run = QPushButton('Run', self)
        self.btn_run.move(350, 200)
        self.btn_run.clicked.connect(self.run)
        self.show()

    def run(self):
        layer = self.layer_cb.currentLayer()
        src_crs = layer.crs().authid()
        if self.length_le.text()is not '':
            length_val = float(self.length_le.text())
        else:
            length_val = None
            self.msg = QMessageBox()
            self.msg.setText('Please enter a length value')
            self.msg.show()
        if length_val:
            temp_layer = QgsVectorLayer('LineString?crs={}'.format(src_crs.lower()), 'Simplified_Line', 'memory')
            temp_layer.startEditing()
            flds = [f for f in layer.fields()]
            pr = temp_layer.dataProvider()
            pr.addAttributes(flds)
            temp_layer.updateFields()
            feats = [f for f in layer.getFeatures()]
            for feat in feats:
                atts = feat.attributes()
                geom = feat.geometry()
                verts = [v for v in geom.vertices()]
                idx_1 = range(len(verts)-1)
                segment_lengths = {}
                vert_list = []
                vert_list.append(verts[0])
                for i in idx_1:
                    dist = verts[i].distance(verts[i+1])
                    if dist > length_val:
                        vert_list.append(verts[i])
                        vert_list.append(verts[i+1])
                vert_list.append(verts[-1])
                new_geom = QgsGeometry().fromPolyline(vert_list)
                new_geom.removeDuplicateNodes()
                temp_layer.startEditing()
                temp_feat = QgsFeature()
                temp_feat.setGeometry(new_geom)
                temp_feat.setAttributes(atts)
                pr.addFeature(temp_feat)
            temp_layer.commitChanges()
            QgsProject().instance().addMapLayer(temp_layer)

W = SimplifyLinesDlg()
  • Thanks for this...unfortunately in my case it's not about straightening or smoothing the line but dealing with GPS drift and also when a track has been traversed more than once so there's multiple lines on the same track that are within about a 10m range of each other. I tried with ranges from 1m to 100m and at lower values it doesn't fix the traverse issue, at 100m it's to wide. The logic needs to include a test for how close lines are to each other and take an average when they are within a distance of each other. I am experimenting using a buffer and then median line as per a comment. – GeorgeC Sep 17 at 1:20
  • 1
    No worries. I didn't fully understand your problem. Since the question title was about line automated line smoothing, I will leave my answer here as it may help someone else in the future. Good luck. – Ben W Sep 17 at 1:35
  • Sorry for not being clear in the question title, I've updated it now. – GeorgeC Sep 17 at 1:41
  • No problem. It was an interesting exercise nonetheless. – Ben W Sep 17 at 1:55
1

This is too large for a comment so I'll put it here, but it's just two ideas you might look at. First, I just used this on some GPS tracks: Dissolve, buffer 10m with dissolve option, add field and give it a simple value like 1, rasterize (GDAL) using that value and outputting a byte raster, thin the raster (GRASS v.thin), vectorize the thin (GRASS r.to.vect) and then smooth the results using SAGA line smoothing. A simpler alternative method would be to run a clean with a large enough tolerance to snap the lines together without undue shape changes (that's always possible). I used the Integrate tool in ArcGIS because I can never get GRASS v.clean to work properly but I expect others can.

0

The process I ended up using was based on a few answers

1 - Skeletonize (multipart to singlepart / explode), Delete small features and Buffer based on Simplifying multiple lines to create central axis?

Tried -but very very slow 2 - Use the HCMGIS based on Is it possible to convert Polygon to centerline linestring? and Finding centrelines from polygons in QGIS? https://community.wolfram.com/groups/-/m/t/1533248

Instead

3 - created QGIS model that

  • a - explode to vertex
  • b - voronoi Poly
  • c - clip by buffer
  • d - poly to line
  • e - explode to vertex
  • f - select all vertices that intersect the lines from step 1
  • g - invert selection
  • h - line to point

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