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How is IDW raster formed?

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IDW algorithm says that it makes a grid and assigns value to each point in grid depending on the distance of separation. From this definition, it looks like the output is set of equally spaced points. However, the next step, formation of raster grid is not explained.
How does the algorithm assign a unique value to a cell/rectangle from equally spaced points.
Are the grid points located at center of cells and then the value at point assigned to cell?

algorithm vector-grid inverse-distance-weighted

share|improve this question

edited Apr 4 at 9:12

Ian Turton♦

50.2k548118

asked Apr 4 at 9:10

sudheeshsudheesh

127

add a comment | 

0

IDW algorithm says that it makes a grid and assigns value to each point in grid depending on the distance of separation. From this definition, it looks like the output is set of equally spaced points. However, the next step, formation of raster grid is not explained.
How does the algorithm assign a unique value to a cell/rectangle from equally spaced points.
Are the grid points located at center of cells and then the value at point assigned to cell?

algorithm vector-grid inverse-distance-weighted

share|improve this question

edited Apr 4 at 9:12

Ian Turton♦

50.2k548118

asked Apr 4 at 9:10

sudheeshsudheesh

127

add a comment | 

IDW algorithm says that it makes a grid and assigns value to each point in grid depending on the distance of separation. From this definition, it looks like the output is set of equally spaced points. However, the next step, formation of raster grid is not explained.
How does the algorithm assign a unique value to a cell/rectangle from equally spaced points.
Are the grid points located at center of cells and then the value at point assigned to cell?

algorithm vector-grid inverse-distance-weighted

share|improve this question

edited Apr 4 at 9:12

Ian Turton♦

50.2k548118

asked Apr 4 at 9:10

sudheeshsudheesh

127

share|improve this question

edited Apr 4 at 9:12

Ian Turton♦

50.2k548118

asked Apr 4 at 9:10

sudheeshsudheesh

127

share|improve this question

edited Apr 4 at 9:12

Ian Turton♦

50.2k548118

asked Apr 4 at 9:10

sudheeshsudheesh

127

edited Apr 4 at 9:12

Ian Turton♦

50.2k548118

edited Apr 4 at 9:12

Ian Turton♦

50.2k548118

asked Apr 4 at 9:10

sudheeshsudheesh

127

asked Apr 4 at 9:10

sudheeshsudheesh

127

1 Answer
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oldest

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1

yes, IDW is usually implemented so that the value of each cell(pixel) is assigned based on the location of the center of this cell(pixel). Raster storage is just an efficient way to store those equally spaced points, but one should keep in mind that it is a "point center" representation in this case, not an "area-based" representation. Note that this is a one step process: the IDW values are computed only for the cell (pixel) center position and stored in a raster. This is because it is not necessary to compute IDW for positions that are not stored, but in theory IDW values could be computed anywhere in the spatial domain of the observation, so not necessarily on a regular grid.

A consequence of the use of this raster model for IDW is that it will only return the exact value of a point if the point is located at the center of the pixel. (IDW is an exact interpolator, which means in geostatistics that it returns the exact value of an input point at the location of this point).

share|improve this answer

edited Apr 4 at 9:32

answered Apr 4 at 9:20

radouxjuradouxju

41.3k144122

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  thanks a lot. solves the mystery.
  
  – sudheesh
  Apr 4 at 9:23
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Is it possible to specify the spacing between grid points? or, what is the spacing when we do an IDW algorithm
  
  – sudheesh
  16 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  the spacing is equal to the size (height or width) of the pixels. So you can select the pixel size that you want. For a precise answer to this question, you should specify the software that you use.
  
  – radouxju
  15 hours ago
  

  
  
  
  

add a comment | 

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1

yes, IDW is usually implemented so that the value of each cell(pixel) is assigned based on the location of the center of this cell(pixel). Raster storage is just an efficient way to store those equally spaced points, but one should keep in mind that it is a "point center" representation in this case, not an "area-based" representation. Note that this is a one step process: the IDW values are computed only for the cell (pixel) center position and stored in a raster. This is because it is not necessary to compute IDW for positions that are not stored, but in theory IDW values could be computed anywhere in the spatial domain of the observation, so not necessarily on a regular grid.

A consequence of the use of this raster model for IDW is that it will only return the exact value of a point if the point is located at the center of the pixel. (IDW is an exact interpolator, which means in geostatistics that it returns the exact value of an input point at the location of this point).

share|improve this answer

edited Apr 4 at 9:32

answered Apr 4 at 9:20

radouxjuradouxju

41.3k144122

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  thanks a lot. solves the mystery.
  
  – sudheesh
  Apr 4 at 9:23
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Is it possible to specify the spacing between grid points? or, what is the spacing when we do an IDW algorithm
  
  – sudheesh
  16 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  the spacing is equal to the size (height or width) of the pixels. So you can select the pixel size that you want. For a precise answer to this question, you should specify the software that you use.
  
  – radouxju
  15 hours ago
  

  
  
  
  

add a comment | 

1

yes, IDW is usually implemented so that the value of each cell(pixel) is assigned based on the location of the center of this cell(pixel). Raster storage is just an efficient way to store those equally spaced points, but one should keep in mind that it is a "point center" representation in this case, not an "area-based" representation. Note that this is a one step process: the IDW values are computed only for the cell (pixel) center position and stored in a raster. This is because it is not necessary to compute IDW for positions that are not stored, but in theory IDW values could be computed anywhere in the spatial domain of the observation, so not necessarily on a regular grid.

A consequence of the use of this raster model for IDW is that it will only return the exact value of a point if the point is located at the center of the pixel. (IDW is an exact interpolator, which means in geostatistics that it returns the exact value of an input point at the location of this point).

share|improve this answer

edited Apr 4 at 9:32

answered Apr 4 at 9:20

radouxjuradouxju

41.3k144122

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  thanks a lot. solves the mystery.
  
  – sudheesh
  Apr 4 at 9:23
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Is it possible to specify the spacing between grid points? or, what is the spacing when we do an IDW algorithm
  
  – sudheesh
  16 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  the spacing is equal to the size (height or width) of the pixels. So you can select the pixel size that you want. For a precise answer to this question, you should specify the software that you use.
  
  – radouxju
  15 hours ago
  

  
  
  
  

add a comment | 

yes, IDW is usually implemented so that the value of each cell(pixel) is assigned based on the location of the center of this cell(pixel). Raster storage is just an efficient way to store those equally spaced points, but one should keep in mind that it is a "point center" representation in this case, not an "area-based" representation. Note that this is a one step process: the IDW values are computed only for the cell (pixel) center position and stored in a raster. This is because it is not necessary to compute IDW for positions that are not stored, but in theory IDW values could be computed anywhere in the spatial domain of the observation, so not necessarily on a regular grid.

A consequence of the use of this raster model for IDW is that it will only return the exact value of a point if the point is located at the center of the pixel. (IDW is an exact interpolator, which means in geostatistics that it returns the exact value of an input point at the location of this point).

share|improve this answer

edited Apr 4 at 9:32

answered Apr 4 at 9:20

radouxjuradouxju

41.3k144122

share|improve this answer

edited Apr 4 at 9:32

answered Apr 4 at 9:20

radouxjuradouxju

41.3k144122

answered Apr 4 at 9:20

radouxjuradouxju

41.3k144122

answered Apr 4 at 9:20

radouxjuradouxju

41.3k144122