I have a set of points inside a polygon. My goal is to figure out how long it takes (in days) for each point to move outside the polygon, based on a daily movement which affects all the points the same way. Once each point leaves the polygon, it should stop moving. Each point has a starting date. I have a table containing dates and the X and Y values by which to shift points on each day (it varies daily). I'll be using this Shift function to move the points. Looking at the table, I'd expect the points to move in one general direction for a week or so before landing outside the polygon.
My process is something like this. FYI, each point has a Start Date (which won't change) and a Current Date, which will be used to look up the appropriate X and Y shift, and will ultimately be used to determine the days it takes for the point to move outside the polygon.
- Select points which are inside the border polygon.
- Iterate over the points, shifting each according to the Current Date and then incrementing its Current Date by 1 day.
- Return to #1.
I have part of a Python script written (below), but I'm still kind of a beginner to Python. My current stumbling block is figuring out how to look up the appropriate shift values in my table based on the Current Date in the point layer, and pass them on to the Shift function to get the points moved each day. Also, since I want to increment the day by 1 when I do that, it seems like I should be adding that step to the Shift function.
Here's what I have so far:
import arcpy import csv #My shift values table is a CSV, I also converted it to an FGDB table def shift_features(in_features, x_shift=None, y_shift=None): with arcpy.da.UpdateCursor(in_features, ['SHAPE@XY']) as cursor: for row in cursor: cursor.updateRow([[row + (x_shift or 0), row + (y_shift or 0)]]) return #Specify input files startPoints = r"C:\GIS\Data.gdb\Start_Points" shiftedPoints = r"C:\GIS\Data.gdb\End_Points" borderPolygon = r"C:\GIS\Data.gdb\BorderPolygon" shiftValuesTable = r"C:\GIS\Data.gdb\DailyShiftValues" #Create a copy of the source file so the output can be compared to the input if arcpy.Exists(shiftedPoints): arcpy.Delete_management(shiftedPoints) arcpy.Copy_management(startPoints,shiftedPoints) #Import the X and Y values to use for shifting from the source CSV and add them to a dictionary #I had tried making the CSV into a dict with the date as the key and a list of the X and Y shifts #as the value #Create Feature Layers from input features arcpy.MakeFeatureLayer_management(shiftedPoints, "pointLayer") arcpy.MakeFeatureLayer_management(borderPolygon, "polygonLayer") #Select points in the source data which are inside the area to be shifted. #These are points which have not yet exited the polygon. arcpy.SelectLayerByLocation_management("pointLayer", "WITHIN", "polygonLayer") #my current problem: shift_features("pointLayer",X Value from Table for the date,Y Value from Table for the date)
x_shift=None, y_shift=Noneinstead of just
codedoes, I mean it assigns no value to the variable but I don't know why that's necessary.