Question

Create Grids of the same size

  • 17 January 2017
  • 5 replies
  • 4 views
D
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Hi,

Trying to create grids in different parts of the world of the same size i.e. 1km in length.

I am using Points which are LLWGS84 as my source and using the "2DGridCreator" I have tried setting the projection to

"SPHERICAL_MERCATOR" also wondered if "_AZMED_" would work, and also wondered about CommonLocalReprojector (but don't have a bounding box set?). I am then wanting to convert everything back to LLWGS84 and then have grids East to West and North to South with the same length i.e. 1km. current output creates the grids but the length changes in different parts of the world?

Any suggestions to set a static length ?

5 replies

jdh
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Are your grids appearing rectangular in LLWGS84, or are they appearing square which indicated that the ground distance is varying?

 

D
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currently I have done the following:

get point location, generate buffer, (to get the bounding box (BoundingBoxAccumulator)) use reporjector destination "_AZMED_" use CoordinateSystemExtractor to get the projection, get the centre point location of the buffer (i.e.. the original point), extract the XY (in the new projection), use the XY and the new projection in the 2DGridCreator, and set the number of rows / columns and set width and height (now in metres), then trying to reproject back to my original LL-WGS84 projection, but it basically puts it in 0,0 position, (using read from source option), if put in the projection I have generated e.g. _AZMED_WGS84_37.52627508_55.7683228358381 this comes up with an error ( I was wondering if I need a revised projection as I have generated new geography i.e. grids from the original Point location?

error msg:

Reprojector_2(TeeFactory): Reprojector_2: Reproject: Could not reproject the geometry of the preceeding feature: Reprojector: Could not create reprojection engine

jdh
Rank
Badge +22

Have you looked into the 2DGridAccumulator>

 

 

I would suggest Points->Reprojector(equidistant projection of your choice)-> 2DGridAccumulator (Grid Type Cell Size, ColumnWidth, Row Height both 1000, Type of Grid Polygon) ->Reprojector(read from feature to LL-WGS84).

 

You may wish to buffer you points to ensure padding of the grid.

D
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I did a similar approach using 2DGridCreator as that also allows me to se the number of cells plus the size, but doing that I get different sized grid in different parts of the world as I assume my projection is trying cover the world and loses accuracy over a local projection once it is converted back to

LL-WGS84

jdh
Rank
Badge +22

I did a similar approach using 2DGridCreator as that also allows me to se the number of cells plus the size, but doing that I get different sized grid in different parts of the world as I assume my projection is trying cover the world and loses accuracy over a local projection once it is converted back to

LL-WGS84

If you are using a AZMED, then yes it will lose accurancy the further away from the origin it is.

 

Is your data continous? ie you want grids that cover the entire world, or do you have specific areas of interest that are scattered all over the place, but not contiguous? If the latter, you will have much better accuracy using location specific projections. If not, an equidistant cylindrical projection should give you the best results. I would try the miller projection.

 

 

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