Question

Non Concentric Buffer - Isochrones

  • 1 August 2017
  • 2 replies
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Hi All, I am trying to create isochrones around the inside of a polygon that are an equal percentage of distance from a point within the polygon (not necessarily an oval) to the edge. see attached image. My thoughts are : chop outer polygon into 100m sections. get the mid point of each section as a node. create lines from each node to the green point. cut these lines by a percentage of their length (say 50%) and create nodes then somehow join all nodes of equal value into isochrones (contours).

Do you think im on the right track? how do i generate the final step of isochrones? ContourGenerator?

Thanks Steve

2 replies

takashi
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Userlevel 2
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Hi @goatboy, this procedure might help you. Assuming that (x, y) is the buffering center coordinates and "scale" is the distance ratio (e.g. 0.5 indicates 50%).

  1. Offseter (Mode: Cartesian Coordinate): Move the polygon by (-x, -y).
  2. Scaler (Scale Origin: 0,0): Scale the polygon by "scale".
  3. Offsetter_2 (Mode: Cartesian Coordinate): Move the resulting polygon by (x, y).

Alternatively the Affiner could also be used with these coefficients. 

A: scale,  B: 0,  C: x * (1 - scale)
D: 0,  E: scale,  F: y * (1 - scale)

0684Q00000ArKXjQAN.png

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Perfect! Many Thanks Takashi, Much appreciated.

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