It is good procedure at this point in all applications to check the depth grid (here dep.ngh) for possible erroneous connections by means of option Test:CheckNodes in the Editor, and to check that triangles all have their vertices in counter-clockwise order, by using triangle test CCW (also in the Editor). The colour table in file ccwcol.col is suitable for use in test CCW : triangles correctly ordered will be coloured green, while clockwise-ordered triangles will be red. Enter file name "NONE" when test CHECKNODES indicates there are no errors in the grid.
1) Use dep.nod as input NODE file. Use option Display:Redraw to display interior nodes; 2) Using option DisplayGroup:Whole:In then :Save to create and activate a rectangular working polygon over the whole model domain; 3) Using option GroupEdit:GenNodes:Delete to delete interior nodes of dep.nod, thus getting boundary nodes of dep.nod for use as boundary nodes of model grid;
4) Use option GroupEdit:GenNodes:DepGrid to read in depth grid dep.ngh as reference depth grid
5) With option GroupEdit:DepMesh, create Cartesian grid using default mesh size = 0.1312 . To display this grid, pick 'Cartesian Grid: ON' before picking ACCEPT;
6) Use option GroupEdit:GenNodes:Clusters with the following default settings in right hand panel : coefficients A0 ,A1, A2 = 0.0, 0.8, 0.0 ** minimum cluster size = 1 starting location : deepest point Toggle Display Clusters option to YES and then pick ACCEPT to see clusters being formed and subsequent selection of their centres of area as nodes for the model grid.
** This means that the number of Cartesian grid meshes in each cluster will be approximately 0.0 + 0.8 * depth + 0.0 * depth**2
7) Save nodes created in 6), then use File option to create output file (e.g usermod.nod) containing model nodes.
8) Check that usermod.nod is identical to mod.nod supplied in demo data.
[Later, try repeating steps 3) to 7), changing mesh size (Step 5 ) and A0, A1, A2, and minimum cluster size to see the effect on cluster size and number of nodes generated].
It is good procedure at this point in all applications to check the model grid (here mod1.ngh) for possible erroneous connections by using option Test:CheckNodes in the Editor, and to check that triangles all have their vertices in counter-clockwise order, by using triangle test CCW (also in the Editor). The colour table in file ccwcol.col is suitable for use in test CCW : triangles correctly ordered will be coloured green, while clockwise-ordered triangles will be red. When CHECKNODES is appplied to MOD1.NGH, the following message will appear:
ERR 16: Poor configuration at/near node number 17 ; <RTN> to continue
This indicates a non-fatal error at the adjacent interior node number 591 ; having only 3 neighbours, node 591 necessarily has at least one poorly shaped triangle in its neighbourhood. This can be corrected by choosing the Edit option and, for instance, merging node 591 with one of its neighbours. For the present, ignore the warning message, press RETURN, then enter "NONE" in response to the prompt for a NODE file name after the message that the grid is free of errors.
Finally, after making sure that the whole grid is visible on the screen, use Edit:Reshape to improve triangle shape throughout the grid and, using File:Saveas , save the resulting grid as mod1s.ngh
The model grid at this stage still extends well beyond the required open boundaries. The following steps describe how to remove unwanted parts of mod1s.ngh using three applications of the Splitter, so as to obtain a model grid, mod2.ngh, which has three open boundaries at locations dictated by modelling considerations. On the open boundaries of mod2.ngh, a computational code of 6 has been assigned to any node at a junction of an open boundary and a sea boundary, and code 5 to other nodes on the open boundaries. The nodes moved in the three splitting operations are shown in diagrams in the User Manual (revised 1994 version).
Before doing the first split, described in the next paragraph, use the Info:NodeInfo option in the Editor to identify nodes 77, 274, 296, 352, 449, 472 and 89 in mod1s.ngh . Plot or sketch this part of the grid and so that you can recognise these nodes later.
While learning, it is a good idea to do one open boundary at a time. For example, load the Splitter and read in mod1s.ngh . Using option Split and [K]eyboard entry of polygon vertices, draw the polygon (9.75,3.75),(8.75,6.75),(11.,6.75),(11.,3.75), entering 'C' to close the polygon. Then choose the endpoints of the polygon side joining (9.75,3.75) and (8.75,6.75) to define the line along which the split is to be made. Choose A (automatic mode) for moving nodes to the splitting line.
Move nodes 77, 274, 296, 352, 449, 472 and 89 in turn to the splitting line. (If the wrong node is identified the very first time the cursor is used during a session, move whichever node is picked but answer "N' when asked if the move is satisfactory. By the second attempt, cursor sensitivity will have been reset automatically to an appropriate value). Note that because 77 and 89 are boundary points, they will not be dropped perpendicularly on to the splitting line as the other 5 (interior) nodes will be, but each must be repositioned manually to the point where the splitting polygon cuts the existing boundary segment.
N.B. IT IS VERY IMPORTANT THAT EACH INTERIOR NODE MOVED TO THE SPLITTING LINE SHOULD BE A NEIGHBOUR OF THE PREVIOUS NODE MOVED, OTHERWISE INVALID GRID CONFIGURATIONS CAN OCCUR.
When all 7 nodes have been moved to the splitting line, enter 'D' to indicate that this side is finished (if the screen blanks out at this point, press the space bar). Pick 'N' to indicate no more sides (because none of the other sides of this polygon intersects the grid). The program will prompt you to enter computational codes for each of the nodes on the new open boundary. Computational codes vary with the model to be used; for the present, use 6 for endpoints and 5 for nodes elsewhere on the open boundary.
The program will then offer the option of saving the portion of the grid inside the splitting polygon (to be ignored in this case) and then the part outside, which should be saved as file MOD1SA.NGH.
Reload the Splitter, using mod1sa.ngh as input and repeat the whole splitting operation using the splitting polygon with vertices (3.,1.), (10.,3.), (11.,1.), (3.,0.). You will need to window in on this boundary with option 'W' before moving any nodes with option 'M'. Use 'W' and 'PAN' whenever necessary to move along the splitting line. Before entering 'D' after all nodes have been moved, be sure to window out until the whole splitting line in use is visible, so that you will be able to see all the markers prompting you for computational codes. Save the required part of the model grid as modisb.ngh .
Again reload the Splitter, using mod1sb.ngh as input and repeat the whole splitting operation using the splitting polygon with vertices (0.5,12.75), (6.5,11.), (6.5,14.), (0.5,14.) . Save the required part of the grid (the part outside the splitting polygon in this case) as usermod2.ngh. Comparing this file with grid mod2.ngh in the supplied demo data may reveal some small differences in coordinate values attributable to the manual repositioning of boundary nodes. More notable differences will show up if the nodes moved differ from those used in preparation of the demo data.
Known splitter bugs at 28 April 1994: On PC's, the screen may blank out when option D is chosen at the end of moving nodes to the splitting line. Press the spacebar to restore the display. If this happens, you may be prompted twice to enter a computational code for the first node. Check afterwards with option Test:Vertices in the Editor and activate tests C5 and C6 to check codes entered on the new boundary. Option Info:Nodeinfo can be used to change the value of a code.
It is good procedure in all applications, whenever a grid has been changed substantially, to check for possible erroneous connections by using Test:CheckNodes, and to check that triangles all have their vertices in counter-clockwise order, by using triangle test CCW in the Editor. In addition, it is a good idea to smooth the whole grid using Editor option Edit:Reshape after open boundaries have been created. Note that Edit:Reshape moves only those interior points visible in the viewing window. Carry out these operations on mod2.ngh and save the resulting grid as mod3.ngh .
When nodes have been moved from their original positions, for instance by using the Splitter or Edit:Reshape in the Editor, their depths at their new positions are evaluated by linear inter- polation among the previous values. The resulting depths are less accurate than if they were calculated by linear interpolation among the vertices of the depth grid dep.ngh . The depths at all model nodes can be improved by using program Redep to reevaluate them by linear interpolation from the reference depth grid dep.ngh
When Redep is run with dep.ngh as reference grid and mod3.ngh as grid to be corrected, the following output appears on screen:
Pts. outside reference grid = [number between 0 and 6 in present example - see below] Marginal points = 357 Negative depths reset = 0
On a 386 PC, REDEP here takes approximately 28 sec; with a grid of approx. 10000 nodes and a reference grid of approximately the same size, REDEP takes about 4 hours.