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Hi, I'm looking to calculate the slope of a raster in a specific direction. For example: if i am standing at a point and facing NE (45 degrees), what is the slope I would be looking up. The math is not to bad, there's a great illustration here: An introduction to the directional derivative and the gradient - Math Insight What I don't know how to do is calculate derivatives in arcgis. Any help would be greatly appreciated. Thanks, Dave
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02-20-2015
09:51 PM
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I wish I could upgrade, but it's not in the budget. And, thanks for the offer to process the data. I'll decline as I still need to determine the angles to be used for each point and incorporate a surface roughness factor to scale the length. Once I have all the pieces together I should be able to find a machine that I can use for a bit. As for the data extraction, I converted the bedrock data to a raster and then used the tabulate area tool to create a table that I can join back to the polygons. Thanks again for your help Xander. I will follow your link on learning python and one day return the favour back to the community!
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02-09-2015
12:43 PM
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Another quick question. Is it possible to have the point ID field recorded as an attribute in the resulting polygon? Thanks again!
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02-08-2015
11:09 PM
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Thank you both. You guys are awesome. Seriously. Xander, will Darren see this? not sure how to tag him. I think the variable sizes and angles will work perfectly. But.. and this is a big one... I am using Arcview 9.3.1, so as far as I can tell, I can't use arcpy. I will try to get access to a machine with a higher version. I'm not familiar with the commands for arcpy, although it appears it's time to learn. With the inputs referenced from the shapefile, you've bang on solved my problem. Don't even want to think about how many hours I could have saved with other problems. So.. I'm not sure if this should be under a new thread, but the next step is to determine the percentage of another layer within each of these polygons. Or, more accurately, the types and proportion of each bedrock unit within each polygon. I've just started researching this, but I thought I should ask you guys before I spend too many hours.. I wish I could thank you guys more for the help. It's much appreciated.
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02-08-2015
06:23 PM
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Hi Xander, Thanks for taking the time to help out. I'll try this tool out, but I need a different shape so it may not be the solution. I'll attach an image from the euclidean direction tool that will hopefully make this a bit clearer. Without getting into too much detail, I need to illustrate an area that may be a source for the point data. In the attached image, the transport direction ranges from 45-90 degrees, hence the cone shape (the transport vectors vary throughout the data set). My only issue is the truncation in the raster due to the close points. I.e, they need to overlap. Another idea is to somehow generate 2 lines at specified azimuths from the points and then use them to intersect with a buffer around the point. This would allow for the overlap that the raster does not accommodate. Pretty stumped right now, so I really appreciate your input and time. Dave
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02-08-2015
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Hi there, I am using arcview 9.3.1 and I need to create oriented buffers from points in a shapefile. The euclidean direction method almost works, but because it calculates to the nearest point, buffers associated with points within the maximum will be truncated. I need each point to have a complete buffer in a specific direction, regardless of overlap with other points. Any ideas would be greatly appreciated. Thanks, Dave
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02-07-2015
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