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artlembo

3,012 post(s)
#12-Feb-18 17:24

I've been looking, but haven't found a function to split an area feature by lines. In 8, there was "Split With" in the transform. Any thoughts?

tjhb

7,907 post(s)
#12-Feb-18 21:54

I think this will come in a batch with or after basic graph functions, especially Gabriel Network, which I think it requires? (Might be wrong.)

Then Relative Network Neighbourhood, Minimum Spanning Tree.

Then routing? (I dearly hope that routing functions will respect line direction, although normalization does not, and even if other graph functions may not.)

artlembo

3,012 post(s)
#12-Feb-18 23:21

Hopefully soon. Not being able to split an area by a line is pretty fundamental to GIS. I just had to revert back to 8 to complete the task.

Don’t think it needs the network functions. It is simply a matter of finding intersections and then breaking the area at the intersection and recycling the coordinates to form the new area.

tjhb

7,907 post(s)
#12-Feb-18 23:37

Yes, you could do it like that, for a small number of objects.

For a large set of lines and/or areas, it becomes a graph problem.

Almost identical to Bounded Areas.

Dimitri


4,754 post(s)
#13-Feb-18 05:06

You can do that today, but a more convenient way will come in the next round of vector editing tools and transforms. It's a common task to want to cut an area at a line, either as part of interactive GIS editing or as part of a transform. We'll have both.

How to do it today? Easy... use the topology overlay Intersect template. Don't even need to use SQL.

Suppose you have a drawing that has a mix of areas and lines. There's a line that crosses an area, like a stream or road that crosses a real estate parcel, and you want the parcel divided into two areas on either side of the line.

1. Create a new area in the drawing where one side of the area follows along the course of the stream and where the rest of the area is bigger than the drawing to be cut. You can use snap to click, click, click remarkably quickly along the course of the stream or road.

2. Select the new area and Ctrl-X to cut it. Paste it into a new, blank drawing. That new drawing is going to be your Overlay drawing.

3. Select the target area in the original drawing so you can use Restrict to Selection to cookie-cut only that one area and not accidentally slice any adjacent areas. Use topology overlay with Intersect to overlay the new area you created as a cookie-cutter over the original area. Done.

You're basically using the boundary of the new area as a cookie cutter to cut along the line that you wanted to use to split the original area into two parts. This technique works fine if you only have a few areas, but obviously it would get tedious if you have many. Also, if the line is intricate along which you want to cut it would be tedious to create the cutting area along the line.. too much zooming in to snap and click.

But, obviously if we can use an area boundary to cookie-cut areas we can use a line. Just a matter of wiring up the templates to make that available in point and click way.

It would also be convenient to have this happen in a generalized way as part of interactive editing, like a Cut With command that uses a given line as a knife to cut an area, etc.

Graeme

916 post(s)
#13-Feb-18 06:40

We use "split with" lines in a temporary drawing created just for that purpose, areas in a target drawing, deleting the lines in temporary after all is done. We do this often, so still do so in 8 until "split with" options arrive in 9.

In 9 we attempted an analogous transform, using "Decompose to Branches", restricting to a selected area with two branches - see screenshot. Our 8 data has many numeric columns with transfer rules (8) set to accommodate different data types, proportional on area for "1-n" being a common one. Checking the options in 9, only "copy" or "ignore" are currently available for this. For "split" type transforms to be workable for attributed objects, we'd need a richer choice. Don't want to labour the point, hoping they'll arrive with the "split" transforms.

Just noted, in the current help topic on transform options, "proportional" / "field drop-down.." isn't listed, very much needed!

9.0.165.1 (downloading 9.0165.2)

Attachments:
Limited transfer rules for numeric fields.jpg

Dimitri


4,754 post(s)
#13-Feb-18 07:21

Don't want to labour the point, hoping they'll arrive with the "split" transforms.

Doing is better than hoping. If there is something specific you need, always send it in as a suggestion.

Just noted, in the current help topic on transform options, "proportional" / "field drop-down.." isn't listed, very much needed!

If you have spotted an error in the documentation, make sure to send in a bug report. If the above is an indirect way of expressing a wish, never fail to send in a suggestion.

adamw


7,818 post(s)
#13-Feb-18 07:55

Regarding proportional transfers - we took them away because we didn't like the way they were defined. If you set field A to distribute proportionally to B, and set field B to distribute proportionally to A, then you have to silently break one of the rules because otherwise you cannot distribute anything.

We are currently considering creating a separate transform to distribute values in a particular field proportionally to values in another field - after the original splitting transform. That way, you'd first perform the splitting transform copying field values, then run a second transform to distribute the values you want to be split proportionally. Maybe we'll find a better way to do this.

If you are mostly distributing proportionally to area / length, that can be special-cased.

Graeme

916 post(s)
#13-Feb-18 08:40

Suggestion sent.

Thanks for the detailed clarification. I see the issue you describe for some scenarios. For our data, it is exclusively distributing proportionately on area.

steveFitz

187 post(s)
#13-Feb-18 21:40

2. Select the new area and Ctrl-X to cut it. Paste it into a new, blank drawing. That new drawing is going to be your Overlay drawing.

I'm new to M9 and trying to get through the manual as well as follow examples on the forum.

I tried several times to follow the above but cannot get Ctrl-X to work. In fact cut, copy and paste are grayed out in the menu.

Using 9.0.165.0

adamw


7,818 post(s)
#14-Feb-18 06:57

This requires 9.0.165.2.

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