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Mapping

Show Profile  The Map Guy Posted: 4 December 2011, 12:11 AM  
Oops - fat fingers cause typos. I meant 407. I'm using 403 for the rest of the farm.

Show Profile  Michael Posted: 4 December 2011, 10:45 AM  
Suggest use 401 for the rest of the farm. No doubt you are motivated by glare off the bright yellow, so reduce the intensity of both 401/403 in proportion.

Show Profile  The Map Guy Posted: 5 December 2011, 1:05 AM  
I had considered that, but the contour detail is rich in parts of the map. Even a well toned down yellow (401) would probably make the rest of the map unreadable.

I may take a photo of the area next time I'm out there (rained off at the moment) and put a link to it on my website so you can see what I am dealing with. I doubt a control would be placed in this area as there are so many better features close by.

Show Profile  Michael Posted: 5 December 2011, 4:43 PM  
Jim! You have the ability to draw contours that can be read through 70% yellow, or any sort of yellow!

Another tack: you are saying this stuff is irrelevant in terms of speed. So it just LOOKS different. In a forest some tree species look very different, if the runnability is the same we just put a vegetation boundary in.

Show Profile  Paul I Posted: 5 December 2011, 5:06 PM  
semi open/scattered trees or broken ground alternatives???? (clutching at straws)

Show Profile  The Map Guy Posted: 7 December 2011, 2:45 PM  
Thanks guys. I'm not going to reduce the overall legibility of the map by darkening the yellow for the sake of a few square millimetres of map, so I'll probably settle for 407. This map has to be read in the dark (Katoa Po).

I have discovered some interesting "tomos". They look like tomos, but they were initially caused by the result of earth movement. We are on the Kaiapo faultline, and the tomos go diagonally across the gullies (and up the sides) and not along the line of the gully. I have used a black v (204) and erosion gully symbol (109) to show the feature. See http://www.jcsmaps.co.nz/katoapo2012/tomo.jpg

This tomo is over 2.5 deep with vertical sides.

Show Profile  The Map Guy Posted: 7 December 2011, 2:49 PM  
Should be 2.5 metres deep

Show Profile  Michael Posted: 8 December 2011, 12:08 AM  
Mmm, must be incredibly detailed. Someone once said if you can't draw the contours without it looking like spaghetti, chances are you either have too much detail (fieldworker should have simplified more), or you are drawing at the wrong scale. You're not trying to put contours down the tomos are you Jim?

Show Profile  The Map Guy Posted: 8 December 2011, 12:47 AM  
No spaghetti (like Kawhia), no contours in tomos, just areas of a myriad of parallel gullies, and form line and dot knolls. Typical Taupo gullies.

Show Profile  Michael Posted: 9 December 2011, 3:45 PM  
There's now a sample map illustrating the NZ Mapping Conventions on the MTBO website. Thanks to Linley for design work on this map.

Show Profile  Michael Posted: 4 January 2012, 2:32 PM  
Some mappers now have experience with the 15m DEM (digital elevation model on a 15m grid) which was interpolated from the topo 20's by Otago Uni Surveying School. It is available on Koordinates. The potential of this is that OCAD v10 can interpolate contours at a given interval from this, say 10m contours.

Koordinates have fixed a bug which created random zeroes when you cropped a rectangle of interest. There still appears to be a systematic shift in the data of up to one grid interval to the west and to the south, when compared to say 20m contours obtained directly. It might be the cropping, it might be the way OCAD treats things. Regenerating the 20's, they don't look to bad although there's some loss of definition. Creating 10's, the in-between ones don't have nearly the ins and outs of the 20's. But it saves you drawing them yourself, if you want a starting point and you don't have anything else.



Show Profile  Michael Posted: 4 January 2012, 2:37 PM  
Jason Markham is one of those who have been experimenting with DEMs. He can't post at present but asks:

Tasman District Council (TDC) have provided Lidar data of the St Arnaud area which the Nelson club will use for a new basemap. Yeah! The data has been provided in ASCII .xyz format (lat, long and elevation) except there is a fourth column of integer values at the end of each row. This column doesn't seem to represent anything concerning the topography as the values range between 1 and 74 (in a non-random distribution with 1 being most frequent and 74 the least). TDC geodata staff haven't been able to enlighten me about this yet.

What does this fourth value represent? Should I delete it before converting the DEM to contours in OCAD?


Show Profile  Martin Posted: 6 January 2012, 10:57 PM  
The 4th column is a measure of intensity

Show Profile  Michael Posted: 7 January 2012, 9:09 AM  
... intensity of what Martin? And what does it mean for the x, y and z?

Show Profile  Martin Posted: 7 January 2012, 12:45 PM  
Quoting from ESRI: http://www.esri.com/news/arcuser/0103/lidar.html
"The intensity value is a measure of the return signal strength. It measures the peak amplitude of return pulses as they are reflected back from the target to the detector of the LIDAR system. Intensity values are relative rather than absolute and vary with altitude, atmospheric conditions, directional reflectance properties, and the reflectivity of the target."

Also... "the ability to generate photographic images from LIDAR intensity data is not widely known"

It appears to be used when LIDAR data is used to create images, for mapping I would delete it and use the x,y,z coordinates.


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