QGIS – Selecting and Exporting Points Inside Specific Polygon Using QGIS

clipexportpoint-in-polygonqgisselect-by-location

I have a problem that is similar to Get Points in a selected polygon.

I have a polygon layer (with +200 features) that represents a road (subdivided by every 100m) and a point layer of a GPS survey driving through the road.

I want to clip all the points of a selected feature from the polygon layer. My problem is that I have +200 features and I need to do this to every feature.

Is there an easier way to do this than manually selecting 200 features individually and exporting the selection?

Best Answer

There is a direct and very easy way to do this. In the Clip tool, press the green cyclic arrows button next to the Overlay layer dropdown menu. That instructs to iterate the operation over the features of the layer.

You'll get seperate layers for each polygon.

For more details check the "Iterative execution of algorithms" article from the QGIS Training Manual.

Related Solutions

ArcPy – Selecting Points Within Polygon and Updating Attributes in ArcGIS

First of all, never use the regular cursors when you can use the data access (da) cursors introduced at 10.1. They are 10 times faster at least. Second, the Spatial Join can do the linking of polygon attributes to points faster than any series of multiple queries. A single Spatial Join and a da search cursor read into a dictionary and then transfer of the dictionary to the original points with a da update cursor will finish a quite large set of points and polygons in about 3 to 5 minutes or less. This assumes you do not want to replace your original points with a new point feature class directly created by the Spatial Join tool. It also assumes that the fsapoly field and fsapoint field are not the same field name. It they are the same name then "1" or "_1" will have to be appended to the fsapoly field name after the spatial join occurs.

This code could transfer many fields if you include the fields in the field lists that create a match between the source and the target. The more fields transferred using this code the more time it will save over other processes. For example: sourceFieldsList = ["TARGET_FID", fsapoly, "FSA_NAME"] updateFieldsList = ["OID@", fsapoint, "FSA_NAME"] will work to fill in the two fields with no other changes to the code.

The use of the da cursors and dictionary transfer data 10 times faster than an attribute join and the field calculator, even without any attribute index on either the source or the target. I have rewritten all of my scripts that used an attribute join and the field calculator to use similar code to what is written below and saved at least 2 hours of processing time so that these steps now process in about 20 to 30 minutes.

# Import arcpy module
import arcpy

# Allow overwrite 
arcpy.env.overwriteOutput = True

# Script user input parameters
polygonLayer = arcpy.GetParameter(0)
pointLayer = arcpy.GetParameter(1)
workspace = arcpy.GetParameter(2)
fsaPoly = arcpy.GetParameterAsText (3) #FSA in FSA_Boundaries
fsaPnt =  arcpy.GetParameterAsText (4) #FSA in Addresses 
sjpoints = arcpy.GetParameter(5) # output of Spatial Join

#Run the Spatial Join tool, using the defaults for the join operation and join type
arcpy.SpatialJoin_analysis(pointlayer, polygonlayer, sjpoints)

# define the field list from the spatial join
sourceFieldsList = ["TARGET_FID", fsapoly]    

# define the field list to the original points
updateFieldsList = ["OID@", fsapoint]

# populate the dictionary from the polygon
valueDict = {r[0]:(r[1:]) for r in arcpy.da.SearchCursor(sjpoints, sourceFieldsList)}    

with arcpy.da.UpdateCursor(updateFC, updateFieldsList) as updateRows:    
    for updateRow in updateRows:    
        keyValue = updateRow[0]    
        if keyValue in valueDict:    
            for n in range (1,len(sourceFieldsList)):      
                updateRow[n] = valueDict[keyValue][n-1]    
            updateRows.updateRow(updateRow)    

    del valueDict

[GIS] Clipping points by a polygon attribute in QGIS

One way for a batch approach would be to:

Use the Point Sampling Tool plugin to add an attribute from the polygon layer to the point layer. That could be the state name. So now your points has an attribute listing the state the point is in.
Use the menu Vector > Data Management Tool > Split vector layer, where the input vector layer is your point layer and Unique ID field is the state name.

Best Answer

Related Solutions

ArcPy – Selecting Points Within Polygon and Updating Attributes in ArcGIS

[GIS] Clipping points by a polygon attribute in QGIS

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