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Mapping

Show Profile  Selwyn Posted: 10 October 2008, 11:41 AM  
Thanks Paul. I have tried Aarque twice over the last 6 months. They say they can't get from their overseas suppliers any more. Had quite a resonable talk with the chapo in the know. He did caution me to get samples from the proposed English supplier I had in mind, as sosme film can have polypropylene added which is less stable.
Have also made enquiries with Gordon Harris who show no interest. Google search within NZ drew a big blank.


Show Profile  Bryan Posted: 10 October 2008, 12:47 PM  
I am lucky enough to have a big roll of film (which work was throwing out a while back as everything is on computers these days) -this should last me a few years.

In regards to the use of images: In my opinion, Google can be used in some instances instead of orthophotos and aerial photos. In the case I mentioned, I also had access to 'high' resolution images from my work but there really was no comparison. Instead of one to two images from my work, I stitched together 15-20 images from Google in Ocad - this removed the distortions as I worked on small pieces. In Google I could see all fence lines, all trees, some sheep and lots of detail but for my work images I could not. What I've found is that this will not always be the case and I'm lucky to be able to have access to different sources and compare before I choose.

Show Profile  Paul I Posted: 10 October 2008, 1:41 PM  
NZ Aerial Mapping has great coverage of photography NZ wide, often photos I order are 1-2 yrs old, some are sharper than others. They can supply standard digital images on CD for about $200. Orthophotos are a bit dearer ???
My experience trying to update Beautiful Hills has been interesting if not frustrating... Having access to a Lidar scan layered over an orthophoto showed there were fundamental distortions on the previous map, in the end after trying to make corrections using the old map it became increasingly more neccessary to start from scratch - however it was not easy exercise, the Lidar shows general land shapes very well but no detail at all, a fieldworker needs to put in a lot of blood and sweat to turn it into something usefull. I would say that the Lidar is superior to poor photogrammetry in dense native forest. I read somewhere that there are some new technologies developing which are better than Lidar. If I find the info I'll post it here.

Show Profile  Martin Posted: 10 October 2008, 8:17 PM  
we had a lecture on Lidar recently, from an American guy who was using it extensively. The latest technology is using photons.

I'll see if I can track down the slides, here is the abstract:

LIDAR or Laser Detection and Ranging is a rapidly maturing technology that provides rapid and highly detailed characterization of natural and constructed surfaces. The elements of LIDAR include a laser and receiver. The laser emits high frequency pulses of coherent light and the receiver times, counts and processes the reflected pulses of light. LIDAR is analogous to RADAR except is sends out narrow pulses of light versus broad radio waves. The laser return power (intensity) is indicative of the reflectance of the surface and the timing provides a measure of distance from the laser. When LIDAR is coupled with a global positioning systems (GPS) and an inertial navigation system in an aircraft, rapid, highly accurate characterization of both the earth surface and above ground structures or vegetation is possible.

Show Profile  Michael Posted: 13 October 2008, 10:22 AM  
There are aerial photos and there are aerial photos. Some are taken high in the sky and Stewart Hyslop can't see the detail in his stereoplotter. Others are low down and Stewart can pick up a sheep. Some are digitised and corrected to agree with a certain map projection, others are not. We all know this and ask certain questions when photos are discussed.

I wonder if there is LIDAR and LIDAR? I think that an aeroplane goes up and collects data. Then that data goes into some software which turns millions of data points into various things including contours. That software might be told to interpret treetops (for a forest company) or the ground (or the water table under the ground) might it not? It might be told to produce accurate contours or smoothed contours? It might be told to look for vertical surfaces (if you are a local body looking for unauthorised buildings)? Etc etc.

I think we might need to learn what questions to ask about LIDAR output.

Show Profile  Martin Posted: 13 October 2008, 11:06 AM  
They spend about 6 months filtering and interpreting the LIDAR data, simplifying it into the output that's available to us. I gather it's quite a manual process.

Show Profile  Michael Posted: 30 October 2008, 11:04 PM  
Continuing from my post of 11 Jul 08 about standardising symbol numbers for symbols hidden on production prints.

We've got another one to propose.

750.2 Cut lines used for boundary of "partial map" so that eg the same part of a big mapped area can be extracted for production prints. Purple dotted line (actually very short dashes).


Show Profile  Michael Posted: 6 November 2008, 3:19 PM  
Don't read this if you're not a regular OCAD user. It's messy. It's obviously not creating a great deal of difficulty, but with a new IOF mapping specification being worked on, it might.

I've been doing the job I hate - tidying up the symbol table on a map. I often refer to a new blank map for unadulterated symbol numbers. I am pretty sure that at some time in the past the green circle was 418 and the green cross was 419, because that's what's in many of my maps with a long history. Now, if you start a new blank map, the green circle is 419 and the green cross is 418.

Why worry? At best, if I were to import a recently made map into one of my older maps, OCAD adds new symbols to the table, ie 418.1 and 419.1 and I have a strange mixture. I end up with circles that could be 418.1 or 419.0, and crosses that could be 418.0 or 419.1. Or the other way round, I said it was messy! That's if I choose the option "import symbols if symbols are different" or "import symbols".

At worst, if I choose "import symbols only if symbol number do not exist", the circles become crosses and the crosses become circles. I am pretty sure this is what happens if instead of "import" you do a copy-and-paste.

I have been vaguely aware of this in connection with black symbols over 510 and brown symbols over 112, but thru a "feeling in my bones" generally use the "import symbols" option.

I would guess the green circle/cross thing came about by accident. The specifications list the circle and cross in the same paragraph "418, 419 Special vegetation feature", and the example circle came first on the old speci and the example cross came first in the current one.

But the other symbol re-numbering happened when symbols were added or deleted from the specification. This is highly likely to happen in the coming revision. Should we be lobbying OCAD for a technical solution to this problem so that we don't have more trouble when the new speci comes out. Or (more powerfully) asking the IOF Mapping Committee to do so?

But maybe I'll wake up as if from a bad dream and someone will have given me the obvious solution?

Show Profile  The Map Guy Posted: 6 November 2008, 4:43 PM  
Tidying up symbols is extremely messy. OCAD9 simplifies it to a degree. You have the "Compare" option which allows you to compare your map symbols against a standard (pressumably the standard ISOM2000)set.

You can also easily select what symbols have been used to create the map in one operation. This culls the unused icons and saves time. Export the ones you need to work on and save in one file. Export the culled ones and save in another file. Once you have done your editing and resaved, merge the two files and resave. BACKUP first.

For those still using OCAD8 (good on you), make friends with someone who is a competent OCAD9 user. The map/icons can be saved in OCAD8 format.

Show Profile  Michael Posted: 8 November 2008, 2:17 PM  
Can you give us a steer on using "compare", Map Guy? I (re)tried it today (vs a new blank map) and the 11 pages of text are mostly inconsequential variations. These include that "colour is blue vs blue" which I suppose comes from slight differences in the recommended colour mix, or perhaps the colour numbering. And they include small size differences on circles and crosses - mine outside-to-outside and the blank map centreline to centreline.

As I didn't create all these symbols, I must suppose they came from variations in the OCAD default symbol set over the years. What I want is a report which highlights the REAL differences.

How do you export used or unused symbols? Must be staring me in the face but I can only see "load symbols".

Show Profile  The Map Guy Posted: 12 November 2008, 12:03 AM  
The easiest way to cull the unused icon symbols on a map is to import the map onto a BLANK map which has the SAME colour table. Only the icon symbols used in the map will be imported.

Show Profile  Bryan Posted: 13 November 2008, 3:18 PM  
Don't know whether this has come up before.

I'm creating a map using New Zealand Map Grid GIS contours so the OCAD map is in NZMG coordinates (and currently oriented to Grid North).

With some clubs creating a master OCAD file combining all their maps in one file, I'm wondering how they are handling magnetic north.
(for all Orienteering maps magnetic north should be at the top of the map).

If the file is oriented to magnetic north, have the clubs thought of how to handle the magnetic north variance? (eg magnetic north in Wellington is approximately 22.5 degrees east of grid north increasing at the rate of approximately 0.5 degrees every 30 years.
A simple rotation of the map every few years will not work as some
symbols get skewed.

Has anyone set and tested the 'Angle' value in the 'Options - Scales' Menu and what value do you use? Has anyone testing changing this value and printing maps oriented to magnetic north with symbols correctly aligned?

Show Profile  Greg Posted: 13 November 2008, 5:23 PM  
Is this really a problem? 0.5 degree over 30 years, I mean no one noticed when a nationals map was 22.5 degrees out a few years ago

Show Profile  The Map Guy Posted: 13 November 2008, 11:51 PM  
I tend to agree with Greg. Most maps are out of date after a couple of years. I thought you'd have access to NZTM co-ordinates Bryan.

I have used the "Angle" value mentioned above when importing a topo map in as a template - used the OCAD projected grid for alignment of the template. I did this to produce a magnetically oriented map. I just used the G-M angle.

Show Profile  Bryan Posted: 14 November 2008, 7:36 AM  
Yes, its not much of a problem. However, I've been mapping for 26
years (I'm showing my age) and this year I updated a map I first
fieldworked in 1983 (Riverside) - it has not changed much. Also, when creating a GIS or database of maps its quite likely that reference data (like 1:50000 topographical maps and 20m contours will not change over time). I have had to rotate some maps before but not because of magnetic variation.

At my work, I have access to NZMG, NZGD2000, NZGC49, NZTM, raw lat and long, local meridional circuits and Australia is even worse. And don't mention the Chatham Islands which is like the Bermuda Triangle and a real pain as it is outside the NZMG system which most clients want (so we just place points in the middle of the sea). I aslo have access to a Canadian software package called FME which can convert between any system.

The contours I'm using are free and in NZMG and given to me in a shape file. And I'm only using Ocad 8 which is limited on coordinate systems.


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