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Difference between a map based grid and a grid

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I imported a dxf from autocad in order to create a grid based map. Now that I have the map based grid I wanted to have my borehole elevations match up with these new elevations. I went through the case study on adjusting DEM grids to fit measured elevations but when I tried to get the residules I got an error saying that I didn't have a grid. Is there a differece between a map based grid and a grid and if so can I turn my map based grid into grid? Thanks.

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RockWare makes a GRD file when you create a Grid-Based Map. If you go back to the menu, you will see the GRD file name.



Tom B

RockWare Inc

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Thanks for the help. Now I have another question. I created a grid based off the residules and then used the grid math function to add it to my original grid. Now that I have this new grid, I tried to use it for my lithology model. In the lithology model I selected upper surface (grid) filter and used the grid I just created. The problem is my surface displays as completely flat. I also created a section from this and got the same problem.

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ASW called in for help, and sent his files to another of our tech support staff. This was the response:

I think the reason that you still are not getting a good match between the borehole tops and the ground surface grid is that their elevations just don't match. Here is a 3D view of your logs, with a surface representing the "GridplusResidules.grd" grid model appended, and a number of the logs stick up above the surface:


So, you might want to review the steps you took to generate the ground surface grid. Ideally, you should:

1. Import into the Utilities datasheet the XYZ points for the DXF contour line vertices using the File / Import / DXF / DXF -> Datasheet option. (Use the Decimation Interval settings to reduce the number of points imported.) Save this listing as an ATD file (File / Save).

2. Use the Map / Grid-Based Map menu option to create a grid model (e.g. DXF.grd) - and optionally a 2D and/or 3D map - of these points. The grid will be produced at the current project dimensions.

3. In the Borehole Manager use the File / Transfer / Borehole Locations -> Utilities Datagrid menu option to transfer the location data for all of the holes to the Utilities.

4. Use the Utilities Grid / Statistics / Residuals menu option to compute the difference between the elevations at the boreholes (input the Easting, Northing, and Elevation columns) and those in the DXF.grd file. You can store the expected value (e.g. the DXF grid value) and the residual (e.g. the difference) in two unused columns in the datasheet.

5. Use the Map / Grid-Based Map menu option to create a grid model of these residual values. Please refer to the Case Study on our website for suggestions regarding the gridding method to use. (Residuals.grd)

6. Use the Grid / Math / Grid & Grid Math option to add the Residuals.grd to the DXF.grd (adjusted_DXF.grd).

7. Use the "adjusted_DXF.grd" file to filter your lithology model (Upper Surface (Grid) Filter) - you may need to play with having a buffer of 0 or 1.

8. Use the "adjusted_DXF.grd" file as the surface to be represented in the Plot Surface Profile line.

Note that lithology models will look a little blocky along the top in areas of steep contours. Reducing the XY spacing of the nodes in your project dimensions may help, and the Z spacing as well. I got a pretty good looking section using a model generated with 75-foot node spacing X and Y, and 3 foot spacing along the Z.

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