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    Figure 1

    Figure 1 Create a plan grid set based on the PCF.

    MS3D Tip: Recommended Method for Creating a TOPO Solid

    There are times during the modeling and planning process when you need a solid of your model bounds clipped by topography in order to code TOPO%. This is what we call a TOPO solid. And although there are several ways to create TOPO solids not all approaches are equal. Some methods yield TOPO solids that are based on the project limits (MS3D Project Settings | Project Limits) and not the required model limits (from the PCF limits - MSCompass | Extent | Model Limits). This may cause irregularities in calculations. Furthermore, these project limit based TOPO solids can be impractical when dealing with rotated or multiple models. In this article you are going to learn Mintecs recommended standard approach to creating an optimal TOPO solid, customized to adequately cover your model bounds

    S T E P 1 - C R E AT E A P L ANAR G R I D S E T U S I NG T H E P C F L IM I T S I N O RD E R TO COV E R T H E E N T I R E MOD E L B OUNDS .From the Data Manager use File | New | Grid Set (Figure 1). Select to define this grid set Based on PCF and with orientation PCF (Model) Plan. Select the PCF that contains your model and then Ok.

    You now will have a grid set covering each level in your model, from the minimum easting and northing, to the maximum easting and northing. But all you really need is the easting and northing limits, as the elevation limit will be clipped by the selected topography

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    S T E P 3 U S E T H E B OT TOM P L AN E O F T H E G R I D S E T TO C R E AT E A P O LYGON OU T L I N E F O R T H E B OT TOM BA S E S U R FAC E .

    Use the function Surface | Create | from Grid Set or Edit Grid | Polygons to create a polygon outlining the perimeter of the remaining plane. The polygon outline along with the model limits are shown in Figure 3.

    S T E P 2 D E L E T E A L L T H E L E V E L P L AN E S I N YOUR G R I D S E T E XC E P T F O R T H E B OT TOM P L AN E .

    Delete all but the bottom plane of the grid set which will act as the bottom limit for your TOPO solid. Double click on your grid set object in the Data Manager to launch the Grid Set Object Properties. On the Planes page, select all the planes except the bottom, then click Delete (Figure 2).

    Figure 2 Delete all planes in grid set except for the lowest elevation.

    Figure 2

    Figure 3

    You may notice that you can create a surface here instead of a polygon, and then skip Steps 4 and 5. But it has been proven that by taking the time to go through the process of densifying the perimeter of the base surface, there will be a much lower risk of finding self-intersections in the final TOPO solid. That is why these steps are in our recommended standard approach

    Figure 3 Polygon outline of the bottom most grid set plane (blue) and the model limits (pink)

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    Figure 4

    S T E P 4 - D EN S I F Y T H E P O LYGON T HAT D E F I N E S T H E LOWER MOD E L L IM I T S .

    Use the function Polyline | Densify to densify the polygon for better triangulation and intersection later (Figure 4). Select a point spacing that is appropriate for your limit size. It doesnt have to be very dense, but there should be several more points than just the four corners.

    S T E P 5 - C R E AT E T H E B A S E S U R FAC E F ROM TH E B A S E P O LYGON .

    Using Surface | Triangulate Surface | Inside Polyline Boundary, create a surface from the base polygon (Figure 5).

    Figure 4 Densify the base polygon to create a superior base surface later.

    Figure 5 Triangulate the base surface from the base polygon.

    Figure 5

    S T E P 6 C R E AT E T H E TO PO S O L I D U S I NG T H E B A S E S U R FAC E AND TO POGRAPHY S U R FAC E .

    Now that you have your base surface, open your topography surface. Use the Surfaces | Intersect Surfaces Tool to intersect these two surfaces into a solid (Figure 6). Select your topography surface as the Primary group surface, and the base surface as your Secondary group surface. Use the Solids and Cut Solid options. This will create a solid of the volume between the two surfaces.

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    After applying the intersection, the final result is the TOPO solid (Figure 7). This solid completely covers your model bounds but is limited by topography. It can now be used to code your model with TOPO%

    Figure 7Figure 7 The final TOPO solid.

    Figure 6 Create a solid that is limited by the base surface on bottom and the topography surface on top.

    Figure 6

    In MS3D 5.0 and higher, you dont need a TOPO solid to code TOPO%. This can now be done straight from a DTM surface. It is still good practice to compare the coded model volume with that of the TOPO solid. Simply generate a partials file using the DTM surface and the TOPO solid, then run procedure pitres.dat using TOPO as the ore%. The volumes should be exactly the same.

    )Hint: