Latest Contributions by PeterWilson

I'm currently busy with a hydrology study where I'm determining the location and structure requirements (culverts & bridges) for a proposed Railway Alignment. My initial assessment is based on the STRM 90m DEM and the size of my DEM is 34 651 X 24 934 cells = 863 988 034 cells. I can't afford to split my DEM or to increase the cells size as its already a coarse cell size. I've used the Flow Accumulation tool within Arc Hydro, the Flow Accumulation tool within the Spatial Analyst Extension; Hydrology Toolbox as well as tried running it from Python hoping for better processing time. The Flow Accumulation algorithm that is being used seems to be hard coded in that it doesn't use any more than 2 GB memory when processing the Flow Direction GRID to generate the Flow Accumulation GRID. Is there a way to use Python; Map Algebra and Numpy to improve my processing time in generating the Flow Accumulation GRID for large DEM's. The current Flow Accumulation GRID runs for almost 72 hrs. Regards ... View more

I'm currently busy with a hydrology study where I'm determining the location and structure requirements (culverts & bridges) for a proposed Railway Alignment. My initial assessment is based on the STRM 90m DEM and the size of my DEM is 34 651 X 24 934 cells = 863 988 034 cells. I can't afford to split my DEM or to increase the cells size as its already a coarse cell size. I've used the Flow Accumulation tool within Arc Hydro, the Flow Accumulation tool within the Spatial Analyst Extension; Hydrology Toolbox as well as tried running it from Python hoping for better processing time. The Flow Accumulation algorithm that is being used seems to be hard coded in that it doesn't use any more than 2 GB memory when processing the Flow Direction GRID to generate the Flow Accumulation GRID. Is there a way to use Python; Map Algebra and Numpy to improve my processing time in generating the Flow Accumulation GRID for large DEM's. The current Flow Accumulation GRID runs for almost 72 hrs. Regards ... View more

I'm currently busy with a hydrology study where I'm determining the location and structure requirements (culverts & bridges) for a proposed Railway Alignment. My initial assessment is based on the STRM 90m DEM and the size of my DEM is 34 651 X 24 934 cells = 863 988 034 cells. I can't afford to split my DEM or to increase the cells size as its already a coarse cell size. I've used the Flow Accumulation tool within Arc Hydro, the Flow Accumulation tool within the Spatial Analyst Extension; Hydrology Toolbox as well as tried running it from Python hoping for better processing time. The Flow Accumulation algorithm that is being used seems to be hard coded in that it doesn't use any more than 2 GB memory when processing the Flow Direction GRID to generate the Flow Accumulation GRID. Is there a way to use Python; Map Algebra and Numpy to improve my processing time in generating the Flow Accumulation GRID for large DEM's. The current Flow Accumulation GRID runs for almost 72 hrs. Regards ... View more

I'm busy setting up a new Arc Hydro model to assess a new Railway Alignment Design. My study area is within Nigeria, but the basins extend considerably far into North Africa. My Study area ranges from 24°N to 4°N and -12.5°W to 16.5°E Using the Albers 1/6 rule strictly: My Standard Parallels are: Standard Parallel1 = 20.5°N Standard Parallel2 = 7.5°N My Central Meridian is: Central Meridian = 3°E Any assistance in either identifying what parameters I need to use for Albers Equal Area Conic or to use a different projection will be appreciated. Regards ... View more

I'm looking for advice in how to construct a conditional statement using Map Algebra in Python that I can include in my script. I want to use a Mosaic Dataset as an input and generate a polygon (simplified i.e. through the centre of the cell) the following statement: OutRas = Con(InRas >= 0 and InRas <= 5, InRas) Any help will be appreciated. Regards ... View more

I've generated a File Geodatabase with an Index (Polygon) ; Spot Heights (Points) per index ; and Contours (Polylines) per index. I'm trying to generate a python script that will firstly generate a Feature Layer per index. The name of the Feature Layer needs to be based on the value within the field called TAG per index. The Feature Layer per index needs to be used as the Boundary within Topo To Raster. The associated Spot Height Point Feature Class based on the index name needs to be used as PointElevation within Topo To Raster ; and the Contour Polyline Feature Class per index needs to be used as Contour within Topo To Raster. The output DEM needs to be named after the Index name found within the TAG field. I've attached print screens of the File Geodatabase, the Index Feature Class and Attribute Table within ArcMap to better understand what I'm trying to achieve. The code that I've generated so far is below, either my sql expression is incorrect because it fails as soon as I try to use it within Make Feature Layer. I've not yet worked out how to get the TAG field value out in order for it to be used as the Feature Layer Name >>> import arcpy >>> arcpy.env.workspace = r'E:\Projects\H109009\Terrain.gdb' >>> index = "Index10kSelected_5m_WGS84" >>> with arcpy.da.SearchCursor(index,["TAG"]) as sCur: ...     for row in sCur: ...         sqlExp = """ {0} = '{1}' """.format(arcpy.AddFieldDelimiters(index,"TAG"),row.getValue("TAG") ...         arcpy.MakeFeatureLayer_management(index, To be replaced with "TAG" value,sqlExp) Any assistance would be appreciated, please be warned, I've just started learning to code. Regards ... View more

I'm currently using ArcGIS 10 and 10.1 and I'm running into problems with my File Geodatabases. If I create a File Geodatabase in ArcGIS 10.0 and open it in ArcGIS 10.1 it does recognize it as a ArcGIS 10.0 File Godatabase as the upgrade status is greyed out. Is this a bug or is there no difference between 10 and 10.1? Regards ... View more

Does anyone know of a way to extract a single contour from a Terrain Dataset. I've generated a Terrain Dataset for our country and need to extract the contour interval for i.e. 0.5m; 1m; 1.5m - 5m. I'm busy with a Sea Level Rise Risk Assessment and need to automatically extract the following intervals which I then can use to generate an inundated area and perform a risk assessment on population and infrastructure. Any help would be appreciated. Regards ... View more

I'm currently busy with a climate change project and I need to generate a buffer from the coastline based on a defined vertical height (i.e. 0.5m; 2m and 5m). The buffer needs to include the area from the coastline inwards towards inland based on a defined vertical height. Please can someone point me towards a tool or set of tools within 3D analyst to accomplish the following. The defined buffer will be used to indentify population at risk; infrastructure at risk and associated value of infrastructure. Regards ... View more

I have multiple feature class that I performed analysis on and for each field that starts with a "t*" and is type "Double". I need to use a UpdateCursor to update the values within each of the following fields. I don't know how to use a list of fields within my UpdateCursor as the field that needs to be updated. In a previous python script that I used to carry out summary statistics I used a python list to summarise the fields that started with a "t*" and were of type "Double". I'm not sure how to combine the two to get the Update Cursor to replace the first field for each update. Any help would really be appreciated. >>>import arcpy ... fc = r'E:\Projects\H109009\Calcs.gdb\Int_NLC_Quats_CommAgricMD' ... cursor = arcpy.da.UpdateCursor(fc,["t75c2","Shape_Area","MD_NLC_Area"]) ... for row in cursor: ...     row[0] = (row[0]*(row[1]/row[2]*100))/100 ...     cursor.updateRow(row) Regards ... View more

I've generated a model in ModelBuilder to automate the terrain preprocessing steps within ArcHydro. I've taken it a step further and generated a python condition script based on an argument supplied by the user to determine if Batch Watershed and Batch Subwatershed analysis is required. I then want to use "Merge Branch" to run the remaining processes as they are the same for Watersheds or Subwatershed. The problem that I have is either Batch Watershed or Batch Subwatershed will run due to the python condition statement and when I add both output to Merge Branch it won't run as its expecting both and not one or the other. I've attached my Python Script and as well as my ArcHydro Model. Python Script: # Import system modules import arcpy #Set the parameters basinType = arcpy.GetParameterAsText(0) try:     if basinType == "Subwatershed":         arcpy.SetParameterAsText(1,"True")         arcpy.SetParameterAsText(2,"False")     elif basinType == "Watershed":         arcpy.SetParameterAsText(1,"False")         arcpy.SetParameterAsText(2,"True") except Exception as e:         AddPrintMessage (e[0],2) ... View more