Latest Contributions by PeterWilson

I'm trying to get my head around the new Mosaic Dataset. I have downloaded all the SRTM 90m DEM tiles for Africa. I would like to create a Mosaic Dataset of all the tiles and use it as input to modeling in ArcHydro. The problem that I have is that one needs to build overviews in order to view ones Mosaic Dataset when zoomed to full extent. The Overviews add Footprints to the Footprint Feature Class which is part of the Mosaic Dataset. The purpose of my Mosaic Dataset is to make available all the SRTM 90m tiles to the user, who will select the tiles that cover their study area and generate a newly mosaiced DEM and project it to a local projection based on the study area. My concern is that the Overview Footprints will confuse the end user as to which tiles cover their study area as large Overview Footprints are generated and added to the Footprints that represent the source tiles. The reason for having to select the individual tiles that cover a defined study area is that the tiles are stored in a Geographic Coordinate System and would have to be exported as a newly mosaiced DEM and projected to a local projection based on the study area. Any assistance in understanding how to manage overviews and pyramids for Mosaic Datasets will be appreciated. Regards ... View more

ArcGIS Macintosh Version. ... View more

Hi I need some assistance from the community. I have been creating AutoCAD dwg files using "Export to CAD" for quiet a while with very few problems. I've created 4 AutoCAD drawings and saved them as AutoCAD dwg (2010). The engineers are complaining the the CAD drawings generated are being read in when Xreferenced as inches and not meters. The CAD drawings are projected to TM30 WGS84 and the units are in meters. I've attached one of the drawings that I have created. When I bring the CAD drawings into ArcGIS the units are meters. Is it ArcGIS 10 at wrong or is it AutoCAD 2010. Any assistance will be appreciated. Regards ... View more

Is there any way of converting a Raster Layer into a Raster Catalog (unmanaged)? We regularly create Raster Layers for a specific study area and there after have to generate a single image that is resampled down to be used within AutoCAD and HEC-RAS. I'm looking for a simple and automated approach to convert the Raster Layer into a Raster Catalog (unmanaged). I then could convert the Raster Catalog into a single image. I cant seem to understand why this is not available as a tool within ArcGIS by right clicking on a Raster Layer and selecting export to i.e. Raster Dataset; Mosaic Dataset or Raster Catalog. ESRI, may need to add this into the next release of ArcGIS, it seems logical. Regards ... View more

I've received an Excel Worksheet from the surveyors that surveyed xsections of a channel that we are looking to upgrade. I've attached a print screen of the Excel Worksheet (Excel_XYZ) received to depict the format of the xsections received. The following fields are found within the Excel Worksheet: ID; Desc; X; Y; Z. The problem that I have is firstly there is a XYZ for the Top Left Bank; Center of Bottom Channel and Top Right Bank. The xsection is missing XYZ for the Left of Bottom Channel and Right of Bottom Channel to generate an accurate representation (XSection_Profile) of the channel. I created additional XYZ to depict the same height for the Left and Right of Bottom Channel based on the width of the Bottom of the Channel. The problem is that the XYZ are grouped into individual xsections by the ID field, but unfortunately the XYZ are in no particular order and by adding additional XYZ for the bottom of the channel any order is further removed. I have come up with a solution, but looking for a more automated approach to apply it, or a better approach that someone else might have thought of. I have made use of the X Coordinate to order the generation of xsection 3D polylines. The only problem is where the rotation of the xsection (XCoord) has two XYZ with identical X coordinates or the order is reversed due to an XYZ being slightly off from the other XYZ. Where the xsections angle are close to being parallel to longitude I alter and use the Y Coordinate. My approach is currently manual by selecting the points that make up the xsection and populating an order field with either the X coordinate or y coordinate alternatively. I'm making using of ET Geowizards "Points to Polyline Z(M) where an order field is used. Any advise or alternative method to my approach would be appreciated. Regards ... View more

I have generated a terrain dataset for South Africa from 20m contours and SPOT shots. In order to eliminate errors in the terrain where there isn't enough data especially low lying areas. I would like to make use of river centerlines to enforce the drainage within the terrain dataset. My proposed methodology is to intersect the river centerlines with the contours and extract the Z values of the contours into the river centerlines. I would then use the polyline Z river centerlines as hard break lines within the terrain dataset. The problem that I have is that I need to ensure that the flow direction of the existing river centerlines that I wish to use is correct and secondly need to assign a stream order (Strahler) to the river centerline segments. I've attached a screen shot of the river centerlines to help explain the problem that I have with the currently available river centerline dataset. There are numerous segments that should be tributaries but do not extended enough to link up with the main river. I'm looking for advice in how I can make use of the available river centerlines to embed into my terrain. Do I eliminate the segments that are not connected to the main river centerlines. What is the most efficient methodology to rectify the river centerlines to a point that they won't add additional error to my terrain dataset, which I then would like to use to generate a river centerline network to build up an hydro data model. Any assistance will be appreciated. ... View more

My previous post regarding running Arc Hydro 1.4 - Batch Terrain Processing identified that ArcHydro does not generate the vector folder where the rasters are to be stored or the file geodatabase where the vector data is to be stored. I received confirmation from ESRI - Arc Hydro Team this morning. I would like to find out from anyone if there is a possible work around that I could use to generate the necessary default locations for the rasters and vector datasets from ArcCatalog. I'm trying to automate the Batch Processing Tool from ArcCatalog as I have a large amount of watersheds to process. Any help will be appreicated. Regards ... View more

I've created a summary statistics dbf table and would like to use the value from MAX_Value as input to the Arc Hydro - Stream Definition Model. The Stream Definition Model requires a value to determine stream which is stored as a Double Variable. I'm looking for a way that when the model runs the value is taken automatically from the following field and placed within the follwing variable to be used by the Stream Definition Model. I have tried to create a new double variable, change it to a list and select the first field and use the context menu to define the value to be inserted by a specified table. After select the table and appropriate field the value is visible within the field. I have tried to link this double variable as input to the Stream Definition Model for the Threshold, but although the model accepts the linked variable, the model is still greyed out. I've also tried inline substitution with no luck. The second problem with this approach is that the value stored within the variable is static, as it does not update unless you use the context menu to select the table and appropriate field. Any advice in how to resolve this and make use of a value within a field or a better approach in taking 0.5% of the maximum value of a Flow Accumulation grid the be used as the Threshold value, would really be appreciated.... I'm currently using ArcGIS 9.3 SP1 and Windows XP SP3 Regards ... View more

I'm tyring to use the stats calculated on my DEM to determine the Stream Threshold for the Arc Hydro tool - Stream Definition. The defualt value is 5000 cells. The prefered value for Stream Definition - Threshold is 0.5% of the Maximum cells. I have created a model that builds raster attributes, sumarises statistics and based on the maximum value calculate 0.5%. The value is currently stored in a table within a file geodatabase. I have created a double variable and selected it as a list which allows me to select the input value to be taken from a table, once I've chosen the stats table it asks what field, where I select the Threshold. The value that I'm trying to use is visible, yet when I try to use inline-variable substitution the input double variable found in Arc Hydro - Stream Definition won't accept inline variable substitution. If anyone can assist in how to solve this or a better aproach in calculating the threshold as being 0.5% of the maximum values of Flow Accumulation Grid. I'm tyring to automate Terrain Preprocessing to batch process an entire continent. Regards ... View more