[GIS] Why are the features in the memory layer not displayed

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I am trying to create a memory layer, I followed the directions from the page below but no points appeared on my map. First I tried typing each line into the python console and I also create a plugin with the same code and still nothing appeared on the map. At some point while I was typing the code into the console, it asked for the projection, so I specified my typical projection (epsg 2272, a state plane coordinate system)

How to create a new empty vector layer programmatically?

I also reviewed
http://www.qgis.org/pyqgis-cookbook/vector.html#memory-provider

I am experimenting with memory layers because I want to include it into a plugin I am developing.

Best Answer

I needed to add the layer to the interface using:

QgsMapLayerRegistry.instance().addMapLayer(vl)

from PyQt4.QtCore import *

vl = QgsVectorLayer("Point", "temporary_points", "memory")
pr = vl.dataProvider()
vl.startEditing()
pr.addAttributes( [ QgsField("name", QVariant.String), QgsField("age",  QVariant.Int),    QgsField("size", QVariant.Double) ] )

fet = QgsFeature()
fet.setGeometry( QgsGeometry.fromPoint(QgsPoint(1260179,432083)) )
fet.setAttributeMap( { 0 : QVariant("Johny"), 1 : QVariant(20), 2 : QVariant(0.3) } )
pr.addFeatures( [ fet ] )
vl.commitChanges()
QgsMapLayerRegistry.instance().addMapLayer(vl)

Related Solutions

[GIS] How to programatically create and add features to a memory layer in QGIS 1.9

Thanks to gsherman above the PinPoint plugin example is perfect.

As I understand it the process is:

Create the layer with the attributes in the construction string
Add said layer to the map registry
Start editing on that layer
Add features and commit the changes

Here is an extract of my code which now works.

layer =  QgsVectorLayer(
          "Point?field=Rec_No:integer&field=Include:string(120)&field=Label:string(120)&field=X:double&field=Y:double&field=Z:double&field=Height:double&field=Project_Re:string(120)&field=NCA:string(120)&field=DayCrit:integer&field=EveCrit:integer&field=NightCrit:integer",
          item,
          "memory")
QgsMapLayerRegistry.instance().addMapLayer(layer)

# Receivers = as in the above example 'Receivers' is a list of results
for i in range(len(Receivers)):

  # add a feature
  feature = QgsFeature()

  X = Receivers[i][3]
  Y = Receivers[i][4]
  feature.setGeometry( QgsGeometry.fromPoint(QgsPoint(X,Y)) )

  # Details = as in the above example 'Details' is a list of results

  if Receivers[i][1] != 0:
    Include = 'Yes'
  else:
    Include = 'No'

  values = [ QVariant(Receivers[i][0]), QVariant(Include), QVariant(Receivers[i][2]),
                         QVariant(Receivers[i][3]), QVariant(Receivers[i][4]), QVariant(Receivers[i][5]), QVariant(Receivers[i][6]),
                         QVariant(Details[0]), QVariant(Details[1]), QVariant(Details[2]), QVariant(Details[3]), QVariant(Details[4]) ]

  feature.setAttributes(values)
  layer.startEditing()
  layer.addFeature(feature, True)
  layer.commitChanges()

PostGIS – Why Are Some Points in PostGIS Layer Not Displayed in QGIS

I believe the two sets of data have different coordinate reference systems. The coordinate values are very different, so you have data showing up in two different areas. You'll need to identify both coordinate reference systems first. After that, you could build two tables and convert one to the other's coordinate reference system, then merge them. Or convert the csv data before importing it to the table's coordinate reference system.

(including sample coordinate values in the question will let me or someone else improve this answer)

Best Answer

Related Solutions

[GIS] How to programatically create and add features to a memory layer in QGIS 1.9

PostGIS – Why Are Some Points in PostGIS Layer Not Displayed in QGIS

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