winddirection

AnitaBuschgens — Mon, 04 Apr 2022 10:11:24 GMT

Does anyone have a suggestion how to create a buffer around a polygon based on windspeed and winddirection? The normal geoprocessing tool 'buffer' is mainly based on distances and thereby creating circles. A want to use these bufferpolygons as riskzones for example atmospheric deposition or as a riskzone during a major fire. I am using arcgis desktop 10.8.1

Re: winddirection

JohannesLindner — Mon, 04 Apr 2022 13:59:10 GMT

Hmmm... My first instinct would be to create an elliptical buffer, with the feature being in the ellipsis focal point that is pointed into the wind.

def elliptic_buffer(in_features, id_field, major, minor, azimuth, out_features): """Creates an alliptic buffer around the input features. in_features: input feature class / layer id_field: name of a unique id field in the in_features major: buffer distance in the major elliptical axis (meters) minor: buffer distance in the minor elliptical axis (meters) azimuth: geographic angle of the buffer (degrees, North = 0°, East = 90°) out_features: output feature class """ arcpy.env.addOutputsToMap = False # read shapes and id shapes = [row for row in arcpy.da.SearchCursor(in_features, ["SHAPE@", id_field])] sr = shapes[0][0].spatialReference # create ellipsis parameters ellipsis_table = arcpy.management.CreateTable("memory", "ellipsis_table") fields = ["X", "Y", "MAJOR", "MINOR", "AZIMUTH", "ID"] for f in fields: arcpy.management.AddField(ellipsis_table, f, "DOUBLE") with arcpy.da.InsertCursor(ellipsis_table, fields) as cursor: for shape, id in shapes: densified_shape = shape.densify("DISTANCE", 10, 10) for part in densified_shape: for point in part: cursor.insertRow([point.X, point.Y, major, minor, azimuth, id]) # create ellipsis for each point of each densified feature (polyline) ellipsis_fc = arcpy.management.TableToEllipse(ellipsis_table, "memory/ellipsis_fc", "X", "Y", "MAJOR", "MINOR", "METERS", "AZIMUTH", "DEGREES", "ID", sr) # translate features, so that each determining point is in the focal point pointed into the wind dist = (major**2 - minor**2)**(0.5) dx = dist * math.sin(azimuth * math.pi / 180) / 2 dy = dist * math.cos(azimuth * math.pi / 180) / 2 with arcpy.da.UpdateCursor(ellipsis_fc, ["SHAPE@XY"]) as cursor: for row in cursor: cursor.updateRow([[row[0][0] - dx, row[0][1] - dy]]) # create output fc arcpy.env.addOutputsToMap = True # add out_features to map out_fc = arcpy.management.CreateFeatureclass(os.path.dirname(out_features), os.path.basename(out_features), "POLYGON", spatial_reference=sr) id_type = [f.type for f in arcpy.ListFields(in_features) if f.name == id_field][0] if id_type == "OID": id_field = "FID" id_type = "LONG" arcpy.management.AddField(out_fc, id_field, id_type) # convert ellipses to polygon (FeatureToPolygon doesn't keep the id_field...) ellipses = [row for row in arcpy.da.SearchCursor(ellipsis_fc, ["ID", "SHAPE@"])] ids = {e[0] for e in ellipses} with arcpy.da.InsertCursor(out_fc, ["SHAPE@", id_field]) as i_cursor: for id in ids: polylines = [e[1] for e in ellipses if e[0] == id] polygon = polylines[0].convexHull() for polyline in polylines: polygon = polygon.union(polyline.convexHull()) i_cursor.insertRow([polygon, id]) elliptic_buffer("TestPolygons", "OBJECTID", 1000, 500, 45, "memory/test")

These are example buffers for a wind from the north east (azimuth = 45°):

Using appropriate major and minor distances according to wind speed would then be a problem of experience or calibration. Generally speaking:

low wind speed: major and minor distance are similar and relatively small
high wind speed: major distance is much greater that minor distance

Edit: For ArcMap, you have to replace all "memory" instances with "in_memory".

topic Re: winddirection in ArcGIS Pro Questions

winddirection

Re: winddirection