Latest Contributions by GarrettBradford

Hi Dan, this is not a data issue and it is not because of cell size difference. I believe it is due to a problem with the geodesic method as programed in the slope tool. To confirm this you can create a constant raster (which should by definition has a slope of 0 everywhere). The code below produces two example using both SRID 4269 ("NAD83") and 26915 ("UTM"). In both cases the error is apparent when slope is calculated using the geodesic method. import arcpyimport arcpy.sa as SA #NAD83 example nad83=arcpy.SpatialReference(4269) arcpy.env.outputCoordinateSystem = nad83 const_ras = SA.CreateConstantRaster(1.0,"FLOAT",0.0001,"-90.1 29.9 -89.9 30.1") slope_ras = SA.Slope(const_ras,"DEGREE",'',"GEODESIC","METER") #UTM example utm15n = arcpy.SpatialReference(26915) arcpy.env.outputCoordinateSystem = utm15n const_ras = SA.CreateConstantRaster(1.0,"FLOAT",10,"779470 3311230 799367 3333922") slope_ras = SA.Slope(const_ras,"DEGREE",'',"GEODESIC","METER") slope_ras2 = SA.Slope(const_ras,"DEGREE",'',"PLANAR","METER") #This shows what the slope should look like‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍ ... View more

Hi Dan, thanks for the reply! Spatial Reference for 1/3 arc-second data: NAD83: EPSG Projection -- Spatial Reference . Sorry if that wasn't clear. Defining Z-units on the input is not required (see the documentation you linked - you can select them when running the slope tool), however, I did try that as a possible fix and I get the same result. I have read the tool documentation in some detail and have not found any answers there. As I said, the output appears reasonable everywhere besides the 90th west meridian. Can you think of any reason the slope of the fitted topographic surface relative to the ellipsoid would generate the types of values I have shown in the attachment? ... View more