The option to combine datasets "spatially" is useful when the images are coincident in time, but cover different spatial extents. Combining multiple datasets spatially can be useful when a watershed lies within the extents of two (or more) datasets such as the Pearl River watershed.
Task 5 will demonstrate the "Combine TINs Spatially" function using precipitation grids from the Lower Mississippi River Forecast Center (LMRFC) and South East River Forecast Center (SERFC). For the sake of simplicity, only a single timestep will be used in this comparison.
Create a New Map Window.
Right‐Click on the "Pearl-Part A" Session.
From the "Sessions and Maps" option, select Add Map Window.
Enter the name "Spatial Combine" for the new Map Window in the dialog that pops up and press OK.
Combine TINs Spatially.
Within the "Spatial Combine" Map Window, right-click on the TIN node and click on "Select DSS paths..."
Switch the Combine TINs method from "Temporally" to "Spatially."
Filter the B-Part to "Pearl River" and the F-Part to "SERFC-QPE."
Select the SERFC-QPE precipitation grid for 30 August 2021 12:00 by highlighting the pathname within the "Available TINs" window and clicking "Add Sel."
Next, change the F-Part filter to "LMRFC-QPE."
Select the LMRFC-QPE precipitation grid for 30 August 2021 12:00 by highlighting the pathname within the "Available TINs" window and clicking "Add Sel."
Select "OK" to add the selected data to the map window.
The LMRFC and SERFC precipitation data for 30 August 2021 12:00 is added to the map window and display basin-average totals from a spatial combination of the two grids.
Zoom in closer to the Pearl River watershed if necessary.
Question: What is the basin-average precipitation total for the Upper Pearl Subbasin on 30 August 2021 12:00 (from the LMRFC+SERFC spatially combined precipitation grids)?
According to the spatially combined precipitation grids, the Upper Pearl Subbasin received an average of 0.12 inches (15625 ac-ft) of precipitation on 30 August 2021 at 12:00.
Note that this value falls between the SERFC (0.13 in) and LMRFC (0.11 in) values for the same timestep since the spatially combined values is considering both datasets.
In this Task 5, we compared a single timestep from two overlapping gridded datasets from different sources. By combining the two datasets spatially, we saw how HEC-MetVue consolidates the overlapping areas from both sources into an updated, spatially combined TIN.
Task 6 will demonstrate the "Both" TIN combination option which combines datasets with variable extents both spatially and temporally.
