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Mapping

Show Profile  Michael Posted: 27 August 2017, 11:56 PM  
The LINZ Data Service is doing some renaming of url's on Tuesday 29 Aug. I don't think it have any effect on my use of the site, except that it will be unavailable 8-11pm that day. Read about it at http://www.linz.govt.nz/data/linz-data-service/linz-data-service-migration-project/changes-lds-dataset-identifiers. Whew, that's a pretty long url...

Show Profile  Rolf Posted: 2 October 2017, 7:16 PM  
How about the mapping at the Sprint events in Australia. Nearly all trees/bush were mapped as semi-open.
http://garingal.com.au/gadget2014/cgi-bin/reitti.cgi?act=map&id=725

I should think it made the mapping a lot simpler.

What did competitors think?

Show Profile  Bryan Posted: 3 October 2017, 1:23 PM  
Just checked the map against google maps and the vegetation is very generalised - areas which I would probably have classed as open run, individual trees or copses, one very distinctive tree or bush have all been classed as semi-open - all quite easy to map with the full range of symbols (bush, tree, white) and to show with clarity at 1:4000. I can also see areas which are shown as semi-open but the aerial clearly shows grass. I would have mapped this differently.

Show Profile  Michael Posted: 9 October 2017, 12:35 PM  
We all map a bit differently:-))

When you have one tree in an open area, its a tree. When you have two trees, its probably two trees. When you have 50 trees its probably open with scattered trees. Within an open/scattered area, all mappers would pick out Tane Mahuta and make it a "tree" but as to whether any of the other 49 would stand out, that's subjective. So is drawing the boundary round it, and whether you pick out clearings within it.

I ran in Oz, it wasn't an issue.

It may be an issue the way we are adding more and more detail to sprint maps. The spec says that most areas should be done at 1:5000 with 4000 the exception.

Show Profile  fraser Posted: 10 October 2017, 6:53 PM  
I would say on the whole New Zealand maps are at the other end of the spectrum and the use of single trees is probably over done. I am probably guilty of that anyway.

What is technically wrong on the aussie map is there are a few areas of semi-open that are below the minimum size of 10 square millimetres. In this case they should be mapped as open or as single trees.

I have drawn what 10 square millimetres looks like, using green, next to a couple of the areas which are below the minimum size.

https://imgur.com/a/URhwu


Show Profile  Michael Posted: 4 November 2017, 9:47 PM  
Mapping conundrum #1234:

I'm using the ISSOM tramway for model railways in parks, largely on a yellow background, and you can hardly see it. The obvious answer is to beef up the lines from 50% to 100% black. Any downside in that? Any other suggestions?


Show Profile  fraser Posted: 7 November 2017, 10:29 AM  
Wouldn't it be better to just use the railway symbol?

Show Profile  Michael Posted: 13 November 2017, 8:02 PM  
It would certainly stand out better. I thought I had found a good way of distinguishing big railways from tiny little ones that you step over without breaking stride. Maybe an almost-invisible line is perfect:-)

Show Profile  Michael Posted: 18 January 2018, 11:37 PM  
Experience with Greater Wellington LiDAR coverage. It was like all my Christmases at once when LiDAR coverage of the Lower North Island (up to Otaki and Eketahuna) became available on the LINZ website. All those areas which had no or dodgy contours could be fixed (although it takes some effort to preserve what fieldworkers have observed).

I have now done three areas and find that quality is variable. A small area in the Hutt Valley , and Tukutuku on the Kapiti coast seemed quite good. The former covered by mature exotic trees was formerly based on 5m city council-supplied contours and I could tell what corresponded to what. Some wiggles were spurious and that's completely understandable. The latter in native bush was formerly based on topo contours interpolated twice down to 5m, the new contours put spurs and valleys in different places but they were mainly wrong where vegetation or steepness meant there had been no fieldwork. It wasn't too hard to blend them in.

It's a different story at Catchpool Valley in Rimutaka Forest Park - another native bush map. We have city council contours but I don't rate them highly - I suspect their terrain model outside the residential area uses coarser data. The GW LiDAR-based contours show greater detail but I'm not sure that I trust them either. There are strange discrepancies such as significant hills on the flat valley floor. The position of some of the "reentrants" along tracks open to the sky leads me to wonder if they have filled in their model with aerial photo-based data.

So. just as with aerial photos and photogrammetry, there may be good LiDAR, and not-so-good LiDAR.


Show Profile  mcroxford Posted: 21 January 2018, 8:36 AM  
http://www.remmaps.it/mag/ an interesting tool for getting the declination right.

Show Profile  Michael Posted: 21 January 2018, 12:24 PM  
Hmmm. Gives a different answer for Wgtn than does GNS. Could be that NZTM is different from UTM in this part of the world.

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