topic Re: Buffer zone according to the surface in ArcGIS Spatial Analyst Questions

Buffer zone according to the surface

RobertoFilloramo — Wed, 04 Apr 2018 17:56:30 GMT

Using ArcGIS (10.3.1), is it possible to create a buffer zone according to the surface with a variable radius (i.e. 5-10-15 Km)? Which means that the buffer zone is not "flat", yet it has a shape that followed the surface.

Thanks

Re: Buffer zone according to the surface

DanPatterson_Retired — Wed, 04 Apr 2018 18:41:05 GMT

Check xander_bakker‌'s solution for surface buffers

Re: Buffer zone according to the surface

RobertoFilloramo — Thu, 05 Apr 2018 10:23:49 GMT

Thank you for replying me.... So I used the Xander's code in my python, it gave me the buffer zones (max dist. 3000) yet it showed an error:

"Runtime error Traceback (most recent call last): File "<string>", line 72, in <module> File "c:\program files (x86)\arcgis\desktop10.3\arcpy\arcpy\management.py", line 3246, in AddField raise e ExecuteError: ERROR 000464: Cannot get exclusive schema lock. Either being edited or in use by another application. Failed to execute (AddField)."

Some suggestions?

Re: Buffer zone according to the surface

DanPatterson_Retired — Thu, 05 Apr 2018 10:27:29 GMT

well that one is pretty well raised when the condition is true. Sometimes, a save, shut down and reboot fixes things to ensure that locks are removed. Don't browse with other applications either

Re: Buffer zone according to the surface

RobertoFilloramo — Thu, 05 Apr 2018 10:32:41 GMT

Ok, I will try to save and reboot the program. Anyway, the obtained raster is not like in the Xander's picture, it is "flat" as I had done it with the buffer wizard

Re: Buffer zone according to the surface

DanPatterson_Retired — Thu, 05 Apr 2018 10:50:43 GMT

everything is in a projected coordinate system I assume and there is a sufficient elevation difference that you will actually 'see' the affect that xander_bakker‌

's script produce? If you have a small elevation difference relative to the buffer, not much is going to be visible unless you compare the result with an intersection with a conventional buffer

Re: Buffer zone according to the surface

RobertoFilloramo — Thu, 05 Apr 2018 11:28:17 GMT

well, my dtm values are High : 927,206, Low : -17,8801. I assume that with these values it should appear different (which means like Xander's pic). I tried another time using some points placed in a more hilly area, yet the circle buffer zones are stil "flat" without any surface adapting.

Re: Buffer zone according to the surface

XanderBakker — Thu, 05 Apr 2018 11:38:43 GMT

Is it possible to share the actual data? Or at least a screenshot (perhaps a hillshade with the starting point and the resulting buffer?) That would really help to see what you have.

Re: Buffer zone according to the surface

RobertoFilloramo — Thu, 05 Apr 2018 11:54:50 GMT

I attached some screenshots: DTM, points, slope, resulting buffer

Re: Buffer zone according to the surface

XanderBakker — Thu, 05 Apr 2018 12:08:52 GMT

Can you share an area of the DEM around a point just big enough for the buffer to fit and the settings (pixsize and steps) you used for the scrip and the resolution of the DEMt? I would like to validate the intermediate results to see what is going on.

Re: Buffer zone according to the surface

RobertoFilloramo — Thu, 05 Apr 2018 12:40:46 GMT

here I can't upload the data, because they exceed the uploading limit... So, the DTM resolution is 8mt, actually I copied your code changing the folder locations and max distance (because all the rest seems correct, at least)

Re: Buffer zone according to the surface

XanderBakker — Thu, 05 Apr 2018 13:57:34 GMT

If you have a resolution of 8mt, you will want to change the setting on line to 8 instead of 30. This will be better, but does not explain why you don't see any influence of the slopes on the resulting buffer. What is your maximum distance? I assume your coordinate system is projected (no geographic).

If you extract a small rectangle around a point I'm sure it will be below 50MB (when stored in a fgdb) and you will be able to attach it to the thread. It is hard to detect what might be wrong without access to (a sample of) the data.

Re: Buffer zone according to the surface

RobertoFilloramo — Thu, 05 Apr 2018 14:51:07 GMT

Yes, my coordinate system is projected and max distance is 3000mt. I attached the sample files (on top)

Re: Buffer zone according to the surface

XanderBakker — Thu, 05 Apr 2018 20:46:21 GMT

Just ran the script with some minor modifications and it does generate a result:

There are some differences in the normal buffer (black line) and the surface buffer (blue line). Will try and check later if the result is really correct.

Re: Buffer zone according to the surface

DanPatterson_Retired — Thu, 05 Apr 2018 20:52:21 GMT

As suspected... visual expectation is not the same as reality.

Re: Buffer zone according to the surface

RobertoFilloramo — Fri, 06 Apr 2018 08:31:37 GMT

So, this discrepancy between the visual expectation and the reality to what is due?

Re: Buffer zone according to the surface

RobertoFilloramo — Fri, 06 Apr 2018 08:38:57 GMT

Thanks.... I tried too, changing the pix size in 8. The code worked without any problems, yet the result is still the same which means that it didn't show any changing as in yours. Moreover, the previous result overlapped the new one perfectly.

I attached two pics: the red line is the new datum, while the black line the old one.

Re: Buffer zone according to the surface

XanderBakker — Fri, 06 Apr 2018 12:12:51 GMT

Are there any buf_3D featureclasses created? This is the actual result of the tool and not the pnt_buf featureclasses. If these are not created the process is not running completely and some error is occurring in the process.

If I select a single line that passes through some relatively steep slopes (line Line_D 357):

... and I extract the slope values, the mean slope is 25.7%:

This would mean that the buffer should pass at 2905 meters from the center point. It passes at 2920. The reason for this difference is that the slope direction is taken into account. If you traverse a steep slope maintaining the same altitude, you will traverse at a slope of 0%. A slope map returns the maximum slope in any direction..

Re: Buffer zone according to the surface

DanPatterson_Retired — Fri, 06 Apr 2018 13:58:03 GMT

As shown in Xander's figures, if there is not significant elevation change, and more importantly perhaps, undulating change, the difference between a buffer that is simply 2D planar versus 3D is going to be insignificant the larger the buffer radius.

If you want to see dramatic results, pick a hill in your terrain whose 2D radius is small (maybe a couple of 100 m), then buffer that. A buffer radius over many hundreds of meters or kilometers is not going to show any significant difference.

The controlling factors

the cumulative affect of the elevation differences from the centre to a point on the buffer radius
the size of the buffer

the greater the first, and the smaller the second is what will produce the most pronounced result

Re: Buffer zone according to the surface

RobertoFilloramo — Sat, 07 Apr 2018 10:49:28 GMT

Well, I checked and I have not a buf_3D, so I guess I will have to try again the code; moreover, if I switch one all the layers created by the code I obtain that just only a buffer has specific info in its attribute table (as you can see in the pics; 1-general, 2-detail, 3-detail with attribute table). Therefore, I could consider it a mistake too.