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reference_book:image_virtualization [2017/07/25 01:06] admin [Limitations] |
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| Functors [[:Calc Cost Allocation Map]] and [[:Calc Pathway Map]] will always report an error if virtualization is required to make their input maps compatible. The reason behind this behavior is simple: virtualization often replicates a cell turning it into many cells with the same value when the resolution of a map increases, but these functors need the input cost map not to have local minimums. Thus, replicating a cell would create local minimum and that would prevent these functors from working properly. | Functors [[:Calc Cost Allocation Map]] and [[:Calc Pathway Map]] will always report an error if virtualization is required to make their input maps compatible. The reason behind this behavior is simple: virtualization often replicates a cell turning it into many cells with the same value when the resolution of a map increases, but these functors need the input cost map not to have local minimums. Thus, replicating a cell would create local minimum and that would prevent these functors from working properly. | ||
| - | Some other functor such as [[:Extract Map Attributes]] and [[:Extract Categorical Map Attributes]] can produce result that is different from the result that would be obtained using the original versions of the map. Typically, this is not a problem if the information produced by these functors is used with care. For example, it is safe to extract the number of non-null cells and multiply by the cell resolution provided that the values are coming from the //same// [[:Extract Map Attributes]] or the //same// [[:Extract Categorical Map Attributes]]. This is possible because map virtualization changes the cell resolution of a map and the number of non-null cells of the map simultaneously, keeping the multiplication result consistent with the one that would be obtained by using the original version of the map. The same is true for all other attributes. | + | Some other functor such as [[:Extract Map Attributes]] and [[:Extract Categorical Map Attributes]] can produce result that is different from the result that would be obtained using the original versions of the map. Typically, this is not a problem if the information produced by these functors is used with care. For example, it is safe to extract the number of non-null cells and multiply by the cell resolution provided that the values are coming from the //same// [[:Extract Map Attributes]] or the //same// [[:Extract Categorical Map Attributes]]. This is possible because map virtualization changes the cell resolution and the number of non-null cells of a map simultaneously, making the multiplication result consistent with the one that would be obtained by using the original version of the map. The same is true for all other attributes. |
| It is also worth noting that certain maps should not be mixed with other maps with different extents/resolutions such as maps representing line features specially roads. Some algorithms might assume that a road is always only one cell wide and the virtualization process might produce a map where this assumption does not hold. | It is also worth noting that certain maps should not be mixed with other maps with different extents/resolutions such as maps representing line features specially roads. Some algorithms might assume that a road is always only one cell wide and the virtualization process might produce a map where this assumption does not hold. | ||