View source for How to combine GeoTIFFs on the Geoshare into a single Grid Overlay using WMS Overlays

[[GeoTIFF]]s can be made available on the [[Geo Share]] and automatically imported using a [[WMS Overlay]]. However, the size of grid datasets sometimes necessitates such a dataset is split up over multiple files, each of which would be offered up as a separate layer of a [[WMS]] and thus a separate ([[timeframe]] of a) [[Grid Overlay]]. In these situations, it is necessary to recombine the individual pieces of the dataset into a single unified whole before using it in calculations.

{{editor location|overlays|dropdown=Combo Overlay}}

{{howto|title=
| Ensure the desired grid data is available as a [[WMS]] from the [[Geo Share]].
| Create a new [[Combo Overlay]] to add all the parts together.
| Create more [[WMS Overlay]]s to obtain the separate datasets.
| {{howtoblock| Depending on whether the datasets are in separate [[timeframe]]s or separate [[Grid Overlay]]s:
    | If the datasets are in separate [[WMS Overlay]]s, ensure each is set as an input for the new [[Combo Overlay]].
    | If the datasets are [[timeframe]]s in one [[WMS Overlay]], ensure that single [[WMS Overlay]] is set as input for the new [[Combo Overlay]].
}}
| Ensure that its clear under which circumstances a dataset does not feature data. From a [[WMS Overlay]], this is the value 0.
| {{howtoblock| Depending on whether the datasets are in separate [[timeframe]]s or separate [[Grid Overlay]]s:
    | If the datasets are in separate [[Grid Overlay]]s, set the [[Combo Overlay]] formula to the following:
    | IF(GT(MAX(A,B,C), 0), MAX(A,B,C), IF(LT(MIN(A,B,C), 0), MIN(A,B,C),0)  ) - If the inputs A, B, and C are used
    | If the datasets are in one [[Grid Overlay]] but separate [[timeframe]]s, set the [[Combo Overlay]] formula to the following:
    | IF(GT(MAX(A0:9), 0), MAX(A0:9), IF(LT(MIN(A0:9), 0), MIN(A0:9),0)  ) - If the datasets span 10 timeframes (0 through 9)
}}
| Ensure the [[WMS Overlay]](s) have obtained any relevant and available data.
| Recalculate the [[Combo Overlay]] to have it combine the datasets.
}}

{{article end
|notes=
* Because a [[WMS Overlay]] does not differentiate between a received 0 value and a NO_DATA value, there is no discernable difference between a 0 as data, or an absence of data.
* The described formulas can easily be expanded by adding additional terms. Either more input letters, or greater values for the last timeframe index.
* The described formulas default to the highest value found among datasets. If the original dataset is cut up properly, even when overlaps exist they should agree with one another in value. If they are not in agreement, either the highest value will be selected (if its greater than 0) or the lowest value (if its lower than 0).
|howtos=
* [[How to load grid values from a GeoShare WMS]]
|seealso=
* [[Geo Share]]
* [[Combo Overlay]]
* [[WMS Overlay]]
* [[GeoTIFF]]
}}

[[Category:How-to's]]