Offset by Elevation

Global Mapper User
edited November 2011
Here's an interesting problem...

I've just been asked by a colleague if I can take a 2D path, and some height data, and produce an offset of the (now 3d) path, simple enough.

except...

The offset needs to be vertical, i.e. I want to show a line that is 12 metres 'down hill' of every segment of the path, which would be simple if the path was flat, i.e. on a contour... but it isn't...

Am I missing a simple way of doing this in GM?

Cheers.

edited December 2009
What you can do is export a XYZ file from the Path Profile dialog, then load that back in using the File->Open Generic ASCII Data File menu command. Press the Point Offset/Scale button on that dialog and specify a Z offset of -12, then you should get a new 3D line imported with the desired offset applied.

Let me know if I can be of further assistance.

Thanks,

Mike
Global Mapper Support
support@globalmappersoftware.com
• Global Mapper User
edited December 2009
Thanks Mike,

Already tried that, unfortunately, that's not the effect I'm after!

The way I'm thinking about the problem is this:

If I wanted to produce an area that represented the terrain that was between 100m and 90m in height, that would be a trivial task.

However, instead of my original contour being at 100m throughout its length, the height varies.

So if i want to produce an area that is between this contour and one at 10m below this variable height contour, I would need to take a point or segment on this line and and find the perpendicular distance at which the underlying topography drops to -10m, i.e. 10m downslope of the given point or segment.

And then repeat for every point or segment.

And then combine these 'downslope' points or segments into a new line.

The effect would be that, for example, on a uniform slope of 1:1 a 10m vertical drop would create a horizontal offset 10m away.. A 1:5 slope would give an offset of 60m etc.

Do you see what I'm getting at?

Cheers.
edited December 2009
Ah, I thought that you were after a 3D line that had the same X/Y location for each vertex, but just 10 meters below. It sounds like what you want is a new line that is on the terrain surface but has the closest points on the surface that are 10 meters below (down-slope) each point in the original 3D line.

Assuming that I understand you correctly, there is not currently any way to automatically compute something like that in Global Mapper. I do think that functionality at least similar to this should be created in GM around the time that we add watershed and flow analysis as that kind of thing would be needed at that time.

Thanks,

Mike
Global Mapper Support
support@globalmappersoftware.com
• Global Mapper User
edited December 2009
Thanks Mike,

Thought as much if I'm honest!

Really looking forward to having this functionality in the future, in the meantime I'm formulating a far less accurate, and far more time consuming way of doing it in 3ds max using poly meshes, booleans, and maxscript.

Keep up the good work.

Cheers.
• Global Mapper User Trusted User
edited October 2011
Hello,
did you have implemented this function ?
It will be very helpfull for hydraulic analysis !
Congratulation for your software
edited October 2011
If you have an elevation grid loaded, just go to the Alter Elevations tab of the Options dialog and specify the desired offset.

Let me know if I can be of further assistance.

Thanks,

Mike
Global Mapper Support
support@globalmapper.com
• Global Mapper User Trusted User
edited October 2011
Hi Mike,
in your post you said to Asheldon "(...). It sounds like what you want is a new line that is on the terrain surface but has the closest points on the surface that are 10 meters below (down-slope) each point in the original 3D line".
For instance, i have a canal project (a line) displayed on a DEM. I'd like to have the same canal line but 10 meters below (down-slope).
I hope i'm clear.
Regards
edited October 2011
For what you want the earlier solution of a Simple ASCII Text File export would work. Just export with the option checked to get elevations from loaded terrain layers and then also provide the desired Z offset on the Point Offset/Scale tab when exporting to shift it down 10 meters (i.e. -10 for offset), then load that file back in.

Let me know if I can be of further assistance.

Thanks,

Mike
Global Mapper Support
support@globalmapper.com
• Global Mapper User Trusted User
edited November 2011
Dear Mike,
i try it but it doesn't work as i'd like. Elevation is modified but not the location of the points.
Do you have an another way to do it ?
edited November 2011
Ah sorry I had the same misunderstanding both times. There is not currently a way to offset a line to where it is some elevation "downhill" from its currently location. This is on our todo list for a future release though.

Thanks,

Mike
Global Mapper Guru
gmsupport@bluemarblegeo.com
http://www.globalmapper.com