Flow direction arcgis plus#

It should be of note that when I run the original filled DEM (non-inverted) through the flow direction tool with the exact same parameters, it spits out a raster that has the expected 8 discrete values. What have done wrong here and how do I fix it? In practice, however, I get a raster that has not 8 discrete cell values but 208 discrete values, from 1-208. In theory, this should give me a raster where the cells are defined as one of 8 discrete values, 1, 2, 4, 8, 16, 32, 64, & 128. I checked the box to make the edge cells flow outward, and I left it at D8, which is what I wanted.

Flow direction arcgis plus#

I specify the new inverted DEM as the input, and choose to save the output as the same name plus 'flow_dir' somewhere in the name. However, when I then move on to the flow direction tool, I get weird results. I threw the two DEMs (inverted and not inverted) into arcscene just to check my sanity and yes, the new inverted DEM showed valleys where previously there were ridges.

This made it so that my inverted and filled DEM had positive values. I modified the equation in the raster calculator to be: (('Rasterlayer' - Max_value) * -1) + Min_value What I found was that in the step where you invert your filled DEM, the resulting raster has all negative values for elevation. Firstly I went through every step exactly as it is shown on that page, and ended up with a shapefile that defined almost every cell in the raster as 'ridgeline.' I went back through in order to diagnose where I went wrong. I followed the directions at How To: Identify ridgelines from a DEM and am having some trouble. 'Extracting Topographic Structure from Digital Elevation Data for Geographic Information System Analysis.' Photogrammetric Engineering and Remote Sensing 54 (11): 1593РІР‚вЂњ1600.My main goal here is to end up with a shapefile that simply defines the ridgeline in a given area. 'Raster and Vector Processing for Scanned Linework.' Photogrammetric Engineering and Remote Sensing 53 (10): 1383РІР‚вЂњ1387. To obtain an accurate representation of flow direction across a surface, the sinks should be filled before using a flow direction raster. This method of deriving flow direction from a digital elevation model (DEM) is presented in Jenson and Domingue (1988).Р”В¬ells that are sinks can be identified using the Sink tool. If two cells flow to each other, they are sinks and have an undefined flow direction. To be considered a true one-cell sink, all neighbor information must be present. However, if a one-cell sink is next to the physical edge of the raster or has at least one NoData cell as a neighbor, it is not filled due to insufficient neighbor information. If all neighbors are higher than the processing cell, it will be considered noise, be filled to the lowest value of its neighbors, and have a flow direction toward this cell. When a direction of steepest descent is found, the output cell is coded with the value representing that direction. If the maximum descent to several cells is the same, the neighborhood is enlarged until the steepest descent is found. Therefore, if the cell size is 1, the distance between two orthogonal cells is 1, and the distance between two diagonal cells is 1.414 (the square root of 2). The distance is calculated between cell centers. This is calculated as follows: maximum_drop = change_in_z-value / distance * 100 The direction of flow is determined by the direction of steepest descent, or maximum drop, from each cell. The coding of the direction of flow Calculating the direction of flow This approach is commonly referred to as an eight-direction (D8) flow model and follows an approach presented in Jenson and Domingue (1988). There are eight valid output directions relating to the eight adjacent cells into which flow could travel. If the Force all edge cells to flow outward option is chosen, all cells at the edge of the surface raster will flow outward from the surface raster. If the Output drop raster option is chosen, an output raster is created showing a ratio of the maximum change in elevation from each cell along the direction of flow to the path length between centers of cells and is expressed in percentages. This tool takes a surface as input and outputs a raster showing the direction of flow out of each cell. This is done with the Flow Direction tool. One of the keys to deriving hydrologic characteristics of a surface is the ability to determine the direction of flow from every cell in the raster.