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I seem to be a bit stuck on what I thought would be quite straightforward.

I've created a fishnet of polygons, all 25 x 25 metres, 100 polygons by 100 polygons.

My main task is to create a relative co-ordinate system based on the distance from a vertex somewhere near the middle of the grid (but NOT the middle), which will be the origin 0,0.

Basically, the polygon square - where the origin sits at the very bottom left of it - will be X=0 and Y=0. The next square to its right will be X=25 Y=0 and so on and so on to the extents in all directions. The increasing blocks of 25 just represent the actual distance in metres from the origin.

I thought I could maybe number the columns and rows of the polygon grid then work from there, assigning an X and Y value based on column and row number but I can't even seem to do that.

Any ideas?

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you could compute the coordinates of the centroid of your polygons (add fields X and Y, then 'calculate geometry'). Then you substract to each coordinate the value of the origin and you have your relative coordinates. This is of course only valid if you don't have a rotated fishnet, otherwise you need to accont for the angle when doing the conversion.

  • i'll have a go at this today. – Sam Mar 14 '14 at 8:23
  • apologies, i must have been feeling fairly slow at the end of the day yesterday, you simply calculate the XY of the centroid and subtract the required constant with field calc in the required attribute. Fairly straightforward, ta. – Sam Mar 14 '14 at 12:17
  • @Sam if this Answer provided or pointed you in the direction of a solution then you should upvote and/or click the green Accept tick next to it. – PolyGeo Mar 15 '14 at 7:21

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