topic Re: ArcMAP 10.4 - Multiple ring Buffer (0.5 m)- Arcpy in Python Snippets Questions

ArcMAP 10.4 - Multiple ring Buffer (0.5 m)- Arcpy

AmilaThilanka — Mon, 02 Jan 2017 04:15:48 GMT

Hello,

I want to create multiple ring buffer starting with 0.5 m, 1 m, 1.5 m, 2 m,..... up to 500 m around point object. I try to do it by Arcpy - 'MultipleRingBuffer_analysis', unfortunately, it takes very long time and end up with displaying an error.

(But I try it 10 m buffer interval 10 m, 20 m, 30 m, .....500 m, it nicely works)

Does anyone have experience of creating a large number of buffers around single point object....?

Since I'm working with Python (Arcpy), It could be the great help for me to have suggestions in python platform.

Thank you very much for kind attention.

Re: ArcMAP 10.4 - Multiple ring Buffer (0.5 m)- Arcpy

DanPatterson_Retired — Mon, 02 Jan 2017 05:33:54 GMT

That many buffers will take an inordinate amount of time because of the construction of the needed geometry. Perhaps if you could elaborate on why you need that fine a buffer size, some alternate solution could be provided.

Re: ArcMAP 10.4 - Multiple ring Buffer (0.5 m)- Arcpy

AmilaThilanka — Mon, 02 Jan 2017 06:12:14 GMT

Sir,

I want to create a grid (Circular-sector grid with 0.5 m in the radial direction and 2.5 milliradians in cross-radial direction). So, I need similar operation like multiple buffers to obtain with 0.5 m in the radial direction. This grid helps me to extract slope information from TIN by every 0.5 m distance pixel.

Re: ArcMAP 10.4 - Multiple ring Buffer (0.5 m)- Arcpy

DanPatterson_Retired — Mon, 02 Jan 2017 07:02:58 GMT

what is your TIN point spacing? Is it in the order of magnitude of 0.5 m? If not, then you can get away with a coarser resolution. You intent still needs to be elaborated on. Obtaining slope on such a fine scale is generally only done when the study area is exceptionally small. Also, what was the resolution of the data used to derive the slope? sampling it at a scale smaller than what it was derived at doesn't mean that the data are reflective of the actual conditions on the ground. You may be trying to obtain data that are not really representative of actual conditions, in which case, you would need to ground truth them... or confirm the results against slope derived from lidar data which I presume you must be using.

Re: ArcMAP 10.4 - Multiple ring Buffer (0.5 m)- Arcpy

AmilaThilanka — Mon, 02 Jan 2017 08:09:16 GMT

Sir,

I'm using LIDAR dataset so I can get minimum 0.3 m spacing and my study area is less than 1 square kilometres. Are there any other tool than MultipleRingBuffer_analysis or to achieve this task...? Since I need a buffer in vector (polygon) format, hope numpy/pythan approach could be applicable.

Re: ArcMAP 10.4 - Multiple ring Buffer (0.5 m)- Arcpy

TieshengWu — Mon, 02 Jan 2017 09:18:45 GMT

Hi Amila,may be you can try python like below:

def circle_poly(x,y,c1,c2,r): #center, start angle, end angel, diameter
ptc=arcpy.Array()
pnt=arcpy.Point()

n=100         # 100 points every arc, or other value
for i in range(0,n+1):        # n is the number of points of the arc
  ang = (c1+(c2-c1)*i/n) * deg2rad
  pnt.X=x + r * math.cos(ang)
  pnt.Y=y + r * math.sin(ang)
  ptc.add(pnt)                 #
return ptc

Then :

pie=arcpy.Polygon(circle_poly(x0,y0,0,359,dia),sr )

By this way, I believe circles can be constructed with no error cause you can control the numbers of points of every arcs.

By the way, It makes me remember my old post of "How many points are need to construct a smooth circle" , I still wonder how the ArcMap platform decide the numbers of a circle.

Re: ArcMAP 10.4 - Multiple ring Buffer (0.5 m)- Arcpy

DanPatterson_Retired — Mon, 02 Jan 2017 13:43:20 GMT

Do be aware that if you are trying to buffer a point at some distance using circle code... say 200 meters... at an increment of 0.5 meters, you are going to have to vary the number of points that represent the circle in an increasing fashion as you move away from the point location. Circles are represented as an n-gon and not a true circle. Even with 360 points per circle, each pair of points will represent a circle sector and the two points at distance from the circle centre form the terminus points of the sector's chord. As you move further away from the center, the chord length increases and the area between sector divisions doesn't remain constant. (at 100 m the spacing between 2 points forming a 1 degree sector is about 1.7453 m.) To retain the representation of about 0.5 meters you will have to increase the point spacing accordingly beyond about 28.7 meters.

I you need to sample at a finite distance from a location, it would be easier to generate a dense fishnet of a desired spacing rather than try to produce points to form circles. A dense fishnet will use fewer points to cover an equivalent area than those needed to using divided circle sectors. The upside to a fishnet, is that the area of each grid cell will remain the same.

Re: ArcMAP 10.4 - Multiple ring Buffer (0.5 m)- Arcpy

TieshengWu — Mon, 02 Jan 2017 14:26:20 GMT

Dan is right. The n value must be varied with diameter according to some formula. A dense fishnet should be better choice.

Re: ArcMAP 10.4 - Multiple ring Buffer (0.5 m)- Arcpy

JoshuaBixby — Mon, 02 Jan 2017 15:45:31 GMT

I agree with Dan_Patterson‌ that it might be worth considering alternative approaches.

Since you are wanting concentric circles, is your expectation that each new buffer distance is a whole circle or a ring/donut?

Re: ArcMAP 10.4 - Multiple ring Buffer (0.5 m)- Arcpy

AmilaThilanka — Mon, 02 Jan 2017 20:52:13 GMT

Thank you so much for the suggestions. Yes, Joshua, It's should be ring/donut. I found an image (attached) which shows the shape. Also, the shape of the patch (pixel) shouldn't be like a square.

Re: ArcMAP 10.4 - Multiple ring Buffer (0.5 m)- Arcpy

DanPatterson_Retired — Sun, 12 Dec 2021 07:19:59 GMT

>>> top = _arc(radius=10, start=0, stop=1, step=0.2, xc=0.0, yc=0.0)
>>> top.reverse()
>>> bott = _arc(radius=9.5, start=0, stop=1, step=0.2, xc=0.0, yc=0.0)
>>> top = np.array(top)
>>> bott = np.array(bott)
>>> close = top[0]
>>> arc = np.asarray([i for i in [*top, *bott, close]])
>>> pnts = arc.tolist()
>>> pnts
[[9.99902524, 0.1396218], [9.99945169, 0.10471784], [9.99975631, 0.0698126],
 [9.99993908, 0.03490651], [10.0, 0.0], [9.5, 0.0], [9.49994212, 0.03316119],
 [9.49976849, 0.06632197], [9.49947911, 0.09948195], [9.49907398, 0.13264071],
 [9.99902524, 0.1396218]]‍‍‍‍‍‍‍‍‍‍‍‍‍

If someone wants to check that this forms a valid polygon (on the iThing, so I can't check)

I have some code that performs arc calculations.

If it does... or needs fixing,

It is designed initially to create the cirular arc from a circle radius, a start and stop angle, then a densification step, centered about an origin (xc, yc). In this example, I just calculated the top and bottom segments. tried to make sure that the arc formed a closed circular arc.

The code is

def _arc(radius=100, start=0, stop=1, step=0.1, xc=0.0, yc=0.0):
    """
    :Requires:
    :---------
    :  radius = cirle radius from which the arc is obtained
    :  start, stop, incr = angles in degrees
    :  xc, yc - center coordinates in projected units
    :  
    :Returns: 
    :--------
    :  points on the arc
    """
    start, stop = sorted([start, stop])
    angle = np.deg2rad(np.arange(start, stop, step))
    Xs = radius*np.cos(angle)         # X values
    Ys = radius*np.sin(angle)         # Y values
    pnts = np.array(list(zip(Xs, Ys)))
    pnts = np.round(pnts + [xc, yc], 8)
    p_lst = pnts.tolist()
    return p_lst‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

You can then generate each sector singly to do the sampling .... I would NOT recommend making a sampling framework in this manner...

Re: ArcMAP 10.4 - Multiple ring Buffer (0.5 m)- Arcpy

DanPatterson_Retired — Tue, 03 Jan 2017 00:42:04 GMT

here is what the sector are of 1/2 degree with a 50 cm separation looks like between 9.5 and 10 meters out from a point. notice, that the circular arc points are not even noticeable, but they are there. You would be better off simplifying the whole analysis using a fishnet or using the code as a sampling tool

here is what 5 degrees looks like

Re: ArcMAP 10.4 - Multiple ring Buffer (0.5 m)- Arcpy

JoshuaBixby — Sun, 12 Dec 2021 07:20:02 GMT

I can't say I understand your approach, but I can say it is technically possible to get what you are after. Although ArcPy's Geometry classes don't do a good job of supporting arcs and curves, one can work with arcs and curves indirectly. For situations such as this, you definitely want to be working with arcs and curves and not approximated arcs and curves.

Below is some code that builds an Esri JSON-compliant Python dictionary containing either circle or ring buffers:

def concentricBuffers(point_geometry, distance, interval, rings=False):
    x = point_geometry.firstPoint.X
    y = point_geometry.firstPoint.Y
    WKID = point_geometry.spatialReference.PCSCode
    
    esri_json = {
      "displayFieldName" : "",
      "geometryType" : "esriGeometryPolygon",
      "spatialReference" : {
        "wkid" : WKID
      },
      "fields" : [
        {
          "name" : "OUTER_DIST",
          "type" : "esriFieldTypeDouble"
        },{
          "name" : "INNER_DIST",
          "type" : "esriFieldTypeDouble"
        }
      ],
      "features" : [
      ]
    }
    
    steps = range(int(distance/interval))
    prev_step = 0
    for step in steps:
        step = (step + 1) * interval
        
        esri_feature = {
          "attributes" : {
            "OUTER_DIST" : step,
            "INNER_DIST" : 0
          },
          "geometry" : {
            "curveRings": [
              [
                [x, y+step],
                {"a": [[x, y+step], [x, y], 0, 1]}
              ]
            ]
          }
        }
        
        if rings:
            esri_feature["attributes"]["INNER_DIST"] = prev_step
            esri_feature["geometry"]["curveRings"].append(
              [
                [x, y+prev_step],
                {"a": [[x, y+prev_step], [x, y], 0, 0]}                
              ]
            )
            
        esri_json["features"].append(esri_feature)
        prev_step = step
    esri_json["features"].reverse()
    return esri_json‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

The code takes an ArcPy PointGeometry, a maximum distance to buffer out, an interval for buffering, and a Boolean indicating circles or rings. The default is Circles, so make sure to set True for rings. The Geometry objects section of the ArcGIS REST API explains why I structured the Python dictionary the way I did.

NOTE: This is designed for projected data, not geographic coordinate system data. Adding geographic support can be done, but it requires additional code.

The code returns a Python dictionary, which can be passed to ArcPy's AsShape to return a RecordSet that can be exported to a feature class using Copy Features.

>>> pt = arcpy.FromWKT('POINT(10 10)',arcpy.SpatialReference(3857))
>>> arcpy.CopyFeatures_management(pt,'in_memory/pt')
<Result 'in_memory\\pt'>
>>> rings = concentricBuffers(pt, 10, 3, True)
>>> arcpy.CopyFeatures_management(arcpy.AsShape(rings, True), "in_memory/rings")
<Result 'in_memory\\rings'>‍‍‍‍‍‍‍‍‍‍‍‍

The code can generate thousands of rings in a second or less, and it takes a second or two to dump a 1,000 ring record set to disk.

Re: ArcMAP 10.4 - Multiple ring Buffer (0.5 m)- Arcpy

DanPatterson_Retired — Tue, 03 Jan 2017 05:08:39 GMT

Well it can be done, by using the arc code and cycling through inner and outer radii.

If that is what you want... the example is for 5 degree sector widths and each sectors points are densified.

I cut out the buffer from 0 to 5 m since the points would be too dense.

Here is 1/4 of a circle with 1 meter buffer/sector widths by 1 degree

As you can see, the sectors are quite thin and I suspect sampling your raster will have several sectors recording the same values

Perhaps you can re-examine the sizes you want in both the x and y direction since you will notice that the sample space changes with the angle, preferring a different axis as the sectors get rotated.

Re: ArcMAP 10.4 - Multiple ring Buffer (0.5 m)- Arcpy

DanPatterson_Retired — Tue, 03 Jan 2017 13:18:10 GMT

of course if you generate your own multiring buffer code, you can vary the density of the points used to create the rings, effective, moving from a dense ngon (360+ points) down to triangles.

Or add in a rotation and scaling factor to the circle and generate ellipse rings.

Re: ArcMAP 10.4 - Multiple ring Buffer (0.5 m)- Arcpy

curtvprice — Tue, 03 Jan 2017 20:15:12 GMT

Dan, can you post the code you used for these? Cool!

Re: ArcMAP 10.4 - Multiple ring Buffer (0.5 m)- Arcpy

DanPatterson_Retired — Tue, 03 Jan 2017 20:49:42 GMT

I'll throw it in a blog and github it if that is ok... just trying to get some stuff ready for classes before next week... so maybe tonight...

Re: ArcMAP 10.4 - Multiple ring Buffer (0.5 m)- Arcpy

curtvprice — Wed, 04 Jan 2017 02:24:16 GMT

Dan, you're a maniac. My classes start next week too and have no idea how you do it all!

Re: ArcMAP 10.4 - Multiple ring Buffer (0.5 m)- Arcpy

DanPatterson_Retired — Wed, 04 Jan 2017 02:36:46 GMT

Sleep is inconvenient and repetitive ... GitHub link plus the images will appear on my blog ... tomorrow 10:00 am Ottawa, Canada... Take a look at some of the other geometry stuff... like the Julia set demo files... It's how I am introducing programming... cool before the cursors...

Re: ArcMAP 10.4 - Multiple ring Buffer (0.5 m)- Arcpy

DanPatterson_Retired — Wed, 04 Jan 2017 21:47:42 GMT

Curtis... here is the link /blogs/dan_patterson/2017/01/04/circles-sectors-rings-buffers-and-the-n-gons