Calculate flattened site pad to "catch" underlying terrain issues

Global Mapper UserTrusted User

I am trying to fill a stream channel to a certain elevation. I drew a line down the channel, adjusted the vertices elevation to the desired fill elevation, buffered the line a few feet and am now trying to "fill" the channel using the "calculate flattened site pad" command on the buffered area. The resulting grid has many issues as it does not "catch" to my underlying terrain and stream banks. Here are the settings and example results are below. The first section view shows where the results do not catch the terrain. The second section view worked better? Really need this to work and any help appreciated!

Here the command projected the site pad way outside the limits of the channel

At this location the command worked much better (other than a little issue on the right) where the site pad extended past the underlying terrain.

Best Answers

• Accepted Answer

Hi Treebeard,

I think you need to take a look at the Combine Terrain Options under the Analysis Toolbar (see screengrab below as a non-specific example).

When combining a "Fill" surface i.e. above the natural surface then select "Maximum" for the Operation. This will have the effect of creating a new (third) surface that comprises only the maximum terrain elevation values. The opposite applies also when combining a "Cut" surface with natural surface you would do the opposite i.e. select "Minimum" for the Operation which would create a new (third) surface comprising only the minimum terrain.

Currently there is no direct way in GM (that I know of anyways?) to directly create a line or area along the "merge" between two surfaces (I have asked about adding this feature previously, but to no avail). The workaround that I use is to create a combined surface with a "Subtraction (Difference) - Signed" operation and then create the zero or 0m contour line which equates to the merge line.

I hope this helps. Combine Terrains is a really powerful part of GM and gets me out of a lot of jams...

Cheers,

/al

• Accepted Answer

Hi Treebeard,

FYI - Here is the forum string from before about creating a merge line/area between two intersecting surfaces in case it is interest to you:

https://www.globalmapperforum.com/discussion/15961/create-vector-line-or-area-along-join-of-two-intersecting-surfaces#latest

Answers

• Global Mapper User Trusted User

If there was a command to buffer a line to the catchpoint - intersection on the terrain that would be awesome!

• Global Mapper User Trusted User

CarrickCon,

Thank you so much for your help on this and several other questions over the last few weeks. The "maximum" approach is saving many intervening steps. I sure wish we could "buffer" to the terrain intersection! Amazing how many things GMapper can do..... if you know creative workflows and how to use the different functions to get there.... Terrain editing of rasters is definitely the way I want to go vs, Civil 3D etc. Especially when I have to bring the modified terrain back into HEC RAS as a raster.

Thanks again, Blue Marble should have you on retainer!

• You are most welcome Treebeard - happy to help!

I agree about the awesome spatial analysis/design tools within GM. It can do most things (certainly offers incredible value for money at its price point), but sometimes I wish the developers sat down with users to take on board common real world/civil engineering workflows and perhaps make them more directly accessible within GM.

The "buffer to terrain" that you suggest is a good example, as is creation of line/area along "merge" between surfaces etc. My personal favourite would be the ability to copy a design centreline vertices to the clipboard (which GM can currently do), but then to modify the vertices in Excel say and paste back into GM's "Feature Vertex List" directly.

Even the nomenclature could be tightened up/made more relevant e.g. "Profiles Perpendicular to Path" = cross-sections in the real world, "Evenly spread elevations between first and last elevation" = apply straight grade in civil engineering world etc.

Anyhow, that's what I think...

Cheers,

/al

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