Qimera Grid Difference Wizard
How to Start
grid Difference option of Layer menu in Main Menu bar
What it Does
This dialog computes the difference between two selected grids and produces a difference grid object in the scene.
General Description
The Grod Difference wizard is used to initiate several kinds of grid-grid and grid-plane queries. Object types that can be queried are selectable through page 1 and page 2 of the wizard, and the type of query to be applied is selected via the query type radio buttons on page 3. The selected query is applied to the specified data objects, and the scope of the query is specified on page 4 of the wizard. By default, the query is applied to the common or intersection area of both input grids. However, a polygon can be used to constrain the query scope to within a certain area.
Whenever you perform grid difference operations the algorithm always works in the following manner.
It determines which grid has the highest resolution (smallest bin size). If both have the same resolution than the first grid (Grid of Interest) is used as the highest.
For each bin of the highest resolution grid the algorithm determines the height at the bin center from the other grid using a distance weighted average interpolation of the nearest bins at the point of interest. Data nulls (holes in the grid) are accounted for in this calculation.
The difference is then determined from the two height values and written to the output file.
In doing the interpolation, if the interpolation point falls in a data holiday or outside the bounds of the second grid then no difference will be determined at that point. The resulting difference grid will have the same cell centers as the highest resolution grid but will be cropped as necessary to include only the grid area in common for both grids (and to account for any further constraints set on page 4 of the wizard). For example, if one grid is fully contained inside the other then the resulting difference grid will only cover that contained area.
Page 1
Select the first grid for the difference operation. Click Next to proceed to the next page of the wizard or Cancel to cancel the operation.
Page 2
Select the second grid for the difference operation. Click Next to proceed to the next page, Back to return to the previous page of the wizard or Cancel to cancel the operation.
Page 3
Select which data to use for the difference operation. Click Next to proceed to the next page, Back to return to the previous page of the wizard or Cancel to cancel the operation.
Page 4
Select the constraints of the difference operation. When loading constraints from a polygon file it is important to note that these files can only be ACSII files. Click Next to proceed to the next page, Back to return to the previous page of the wizard or Cancel to cancel the operation.
Page 5
Review your selected options for the difference operation. Click Finish to proceed or Cancel cancel the operation. When complete, a Fledermaus static grid will be added to the project representing the results of the grid difference operation. You will also see the statistics for the grid difference.
Grid Statistics Summary Dialog
This dialog displays the resulting statistical information from the grid difference operation. You can save the statistics to a text file using Save Text As button.
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