Latest Contributions by PeterWilson

I'm currently busy with my Masters Thesis where I'm looking into the uncertainty within DEM's generated from different source datasets for hydrological modelling. I came accross the following paper:http://www.hydrol-earth-syst-sci.net/14/1153/2010/hess-14-1153-2010.pdf by THengl 2010. The auther used point datasets to generate the DEM and to generate the variogram model. I've got very little experience in Geostatistics and need help\advice from the community if I can apply the following by converting my DEM to points for the variogram model. Two of the three DEMs will be generated from contours (generated from stereo images and 3D river centrelines), the third DEM is the hydroSHEDS STRM 90m DEM. The reason for choosing the following is based on the current research that I've done so far and determining the uncertainty within the location of the generated river network from two flow routing algorithms (SFD = Single Flow Direction and MFD = Multiple Flow Direction). ... View more

I've been using the STRM 90m DEM for determining hydrological characteristics for projects that we are working on in Africa. To date I've found very few anomalies within the DEM. The only drawback with the SRTM 90m DEM is that the the river reaches (flowpaths) are not always well defined which affects the hydrological characteristics. I've recently downloaded the HydroSHEDS updated version of the SRTM. I'm currently busy with a project and decided to use the HydroSHEDS DEM to derive the hydrological characteristics and found that the DEM has anomalies\artifacts (i.e. stripping) that run through the DEM that looks likes squares most probably introduced during the merging of tiles. Is there anyway of removing these systematic errors from the DEM without grossly altering the DEM? I've come across some users using Fast Fourier Transforms filter to remove systemtic errors from DEM. I'm not sure how to apply the following within ArcGIS. Any suggestions are welcome. I've attached an example image of the systematic errors. Regards ... View more

I'm currently building a python script that will iterate through Feature Datasets within a File Geodatabase. I then want to create a  new set of Feature Datasets based on the current Feature Datasets but with a different spatial reference. I want to select the Feature Classes within the original Feature Dataset and project and save them into the newly created Feature Datasets. I want to use arcpy.da.walk to firstly get a list of the Feature Datasets in order to create the new Feature Datasets, but for some unknown reason even if I set the datatype to "FeatureDataset" nothing is returned. Any assistance to resolve the following will truly be appreciated. Also if someone can guide me in how to only retrieve the Feature Classes in the Feature Dataset and not directly within the File Geodatabase and how then to save the the reprojected Feature Classes into the newly generated Feature Datasets. ''' Created on Aug 25, 2014 @author: PeterW ''' # Import system modules import arcpy import os # Set current workspace workspace = r'E:\Projects\Projects14\H103342\test2.gdb' arcpy.env.workspace = workspace # Set environment settings arcpy.env.overwriteOutput = True # Create list of Feature Classes in each Feature Dataset fcs = [] # Iterate through each Feature Dataset within the File Geodatabase for dirpath, dirnames, filenames in arcpy.da.Walk(workspace, datatype = "FeatureDataset"):     for filename in filenames:         print filename Regards ... View more

I've created the following python script that extracts the position along a polyline based on a user defined interval. The chainage is determined for each point (i.e. first point = 0 ; second point =50m ; 100m ; 150m ; .... last point = 452m) The problem that I have is that it works great for a single polyline but as soon as you have more than one polyline there is no way of knowing the ID (Cross Section ID) that the points were derived from. I'm using the ArcPy Data Access SearchCursor to find the positions along the line based on the user defined interval and then the list of points are used to create a point feature class with the chainage added as a new field. I was orignally helped by someone else with adding the chainge (distance) values to the pts list using the python zip function. I need assistance extracting the ID field from the polyline and adding the ID value to a new field within the points feature class that is being created. Any help would be appreciated. I've attached my python script as you can't paste within GeoNET . The old user forum was so much better. Regards Peter Wilson ... View more

I'm currently busy with my Masters Thesis "Analyse the Impact of DEM Uncertainty within Hydrological Modelling using Geostatistics". I'm developing a python geostatistics model  that runs a monte carlo simulation (conditional sequential guassian simulation) 1000 iterations where the DEM is altered simulating error and a stream network is derived. The 1000 simulated river networks are used to determine where the biggest uncertainty lies within the derived river network. The following requires that I run Flow Accumulation a 1000 times for my study area. I'm looking for advice from the community that have sucessfully multiprocessed grid processes such as Flow Accumulation or Flow Direction, where each cell is visited to determine the accumulation or direction. How can I subprocess th following with python to improve the performance of my model. Regards Peter Wilson ... View more

Help Please I'm looking for some advice in how to build a LCPA (Least Cost Path Analysis) model using ArcGIS and Spatial Analyst. I want to build a model that determines the Least Cost Path to service all the potential clients with effluent recycled water from the WWTW (Waste Water Treatment Works). I need the model to account for each user before defining the Least Cost Path. So far I've built a model using ModelBuilder using Weighted Overlay Tool to generate the Cost Raster; Cost Distance using the Bulk Pipeline Route; Cost Path to determine the cost path from the users (Land Parcels) to the Bulk Pipeline and convert the cost path from raster to polyline. I've attached jpegs of: Preliminary route Bulk Pipeline (Red) and Feeder Pipeline (Blue) with the identified Users (Land Parcels) titled CapeFlatsNetwork. Location of the WWTW. Feeder Route to Users LCPA Model (ModelBuilder) Any advice in how to build a LCPA for Pipeline Networks, will truly be appreciated. Regards Peter Wilson ... View more

I've found numerous articles that speak about "Burning Streams" and "Building Walls" as part of reconditioning a DTM, epsecially within an Urban Environment. What I've not found is a best practices document that explains how to implement the follwowing within an Urban Environment. My study area has gentle slopes and has man made structures (Bridges and Culverts) within it. I've attached a print screen of a section of my study area that I'm working within. The section displays a road section that has multiple culverts along the road section to ensure the overland flows doesn't go over the road. I've burned streams (culverts) along the roads where the culverts are located to get Arc Hydro to generate the drainage lines at the following locations, but the drainage lines are still crossing the road surface. I'm not familiar in using the "Burn Stream" in combination with "Build Walls" to ensure the flow goes through the culverts and not over the road section. If anyone that is familiar with the following workflow especially within an Urban Environment, I'd greatly appreciate your advice and assistance. I'm looking for a workflow in being able to generate a hydrologically correct DTM from my LiDAR Terrain for use within Arc Hydro. Regards ... View more