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Online Mapping Course Returns

Maps and the Geospatial Revolution

This free online course is back again.

Learn how advances in geospatial technology and analytical methods have changed how we do everything, and discover how to make maps and analyze geographic patterns using the latest tools.

Continue reading Online Mapping Course Returns

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Queensland Globe – Nearly Nearmap

Earth from space

Queensland Globe free spatial data

We’ve taken the loss of Nearmap hard but now here in Queensland is something pretty close. I have to say I’m very relieved.

Queensland Globe (QG) is a Queensland Government open data initiative which uses Google Earth (GE) to present a variety of spatial data and they are progressively adding more.

[button link=”http://www.nrm.qld.gov.au/mapping/queensland-globe.html” style=”info” color=”orange” window=”yes”]Learn more of QLD Globe[/button]

Queensland Globe Pro

You will want to use qglobepro instead of regular qglobe, but it’s hidden away. Download the .kml file, open it and GE will start up with checkboxes for QG data in the Layers pane on the left.

[button link=”http://globe.information.qld.gov.au/GoogleInstall/qldglobepro.kml” style=”download” color=”aqua” window=”yes”]QLD Globe Pro kml[/button]

Remember you need to switch off terrain features or you will have a parallax view which is no use for mapping:

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  1. In GE: Tools / Options / 3D View / Elevation Exaggeration = 0.01.
  2. In the QG checkboxes: Terrain = Off.

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Queensland Globe screen
Queensland Globe screen

Here is why Queensland Globe is special

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  • The aerial photography is reasonably up to date in the areas I have looked; it’s not as good as Nearmap, but a lot better than Google Maps (GM).
  • The aerial photography has been selected for clarity, unlike GM, which can be murky, shadowed and useless.
  • The orthorectification of the aerial photography appears to be quite accurate.
  • Photography is high definition – again better than GM but not as good as Nearmap.
  • It has 10m contours which look reasonably good.

[/unordered_list]

But Queensland Globe is not perfect:

[unordered_list style=”red-x”]

  • No georeferencing information is available, but see below.
  • Contours disappear when you zoom in very close.
  • Cadastre is unreliable and sometimes appears only when zoomed out too far for usefulness. Just keep trying.
  • Images can’t be downloaded, you have to take screenshots.

[/unordered_list]

Georeferencing

Here is how to add georeferencing information to the GE / GQ image. Download the Gridlines Manager .kml file.

[button link=”http://nearby.org.uk/google/Gridlines_mgrs.kml.pl” style=”download” color=”aqua” window=”yes”]Gridlines Manager kml[/button]

This one appears in the Place pane in GE (I’m not sure how or why) and will remain there for future use. (It seems to be necessary to load the QG KML file each time.) Switch on 0.1km grid lines as well as the QG imagery and contours, take a screenshot and you have an image which you can easily load into Ocad and print out for fieldworking.

Once again the gridlines are not entirely reliable, sometimes they don’t display, I think because the system relies upon the availability of a server somewhere to provide the data.

How to load the image in Ocad? I find it’s easiest to import a GPX track somewhere in the vicinity of your map, as this fixes up your map’s Coordinate System, Zone and Offset, and locates you near where you want to be. Now in Ocad go to Map | Set Scale etc and set a grid distance of 100m. Switch on the grid and you can now load the QG image and adjust to the gridlines.

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OCAD Adds Co-ordinate System for Nearmap

NearMap logo

A Mercator projection for Nearmap imagery

Grounded Patterns near Bendigo
Grounded Patterns near Bendigo

In testing Nearmap’s not-for-profits’ plan, Russell Rigby of NSW reported that after analysis;

  1. The Google Mercator units aren’t even close to metres so current Nearmap imagery cannot be imported straight into OCAD at a meaningful scale.
  2. The OCAD transformation [via registration of image corners to OCAD map] from Google Mercator to Map Grid of Australia is good, but needs testing in more areas to be sure.

Following further investigation by Russell and myself we determined that the EPSG code 3785 referenced by Nearmap was not present in OCAD’s co-ordinate system range. Further detective work showed that OCAD contains the original version of the Google Mercator projection (EPSG 900913) but it is no longer officially in use. Not that a cursory search of the spatial world would tell you that. Fortunately Russell came across this post in Alastair Aitcheson’s spatial blog.

Popular Visualisation CRS / Mercator

I advised OCAD hq of the issue along with the background we discovered and they got onto the matter immediately. Their recent service release 11.1.5.1351 of 2013-09-04 contains the co-ordinate system referenced by Nearmap images available under the latter’s Basic plan. In the OCAD co-ordinate system list it is named Popular Visualisation CRS / Mercator (EPSG 3785). Note this addition is not documented in the release notes.

OCAD EPSG 3785

Images previously downloaded via Hypertiles

If you downloaded images via Hypertiles before Nearmap closed off the free service, then you should find those images are georeferenced. Thus if used as a background image, the images will register nicely with a georeferenced map.

You can check the co-ordinate system of such images by opening the .vrt file that is in each Hypertiles data set. The first few lines show;

[quote] <VRTDataset rasterXSize=”75677″ rasterYSize=”113090″>
<SRS>EPSG:28355</SRS>[/quote]

The EPSG reference can then be looked up at spatialreference.org. In this case [quote]EPSG:28355: GDA94 / MGA zone 55[/quote]

However, whichever you selected when running Hypertiles, OCAD should convert nicely.

Russell Rigby on trialling Nearmap’s Basic plan

(Nearmap’s Basic plan offered to orienteering appears to be the same as, or very similar to, their Photomaps Standard Plan).

There is no equivalent of Hypertiles now, where you can nominate the area and resolution level that you want ( at least at the subscription level that is in any way likely).

The current subscription model has a download limit (50MB/month basic, next level 250MB/month). Any image displayed on the screen is included in downloads, to the extent that Nearmap suggests reducing the size of the browser window as a way of reducing the downloads. Panning or zooming adds to the download, as does viewing an image sequence. Using the screen tools (measuring, area, lat/long etc) does not add to downloads as long as the image is not moved.

There are two choices when saving an image. The first is to effectively capture the screen, the second is to define a box to download at high resolution. Both options can generate a world file, in the format attached to the image I sent previously. The only indication of the size & resolution of the resulting image file comes after the download has been requested and performed, so working on a tight download budget could be difficult.

The jgw is the only world-file format – there is no equivalent of the vrt file. Nearmap help suggests loading the output files into a GIS system (ESRI, Mapinfo etc) to work further with the image.

In the test data area Level 17 corresponds to approx 1m pixel size (1.19 “units”), and each change in level corresponds to a factor of 2 eg level 18 == 0.5m pixel. The only way I can see to control download size is to measure the max dimension of the area I want, & do a quick calculation of which scaling level will give between 3k & 6k pixels along that dimension, or I get to level 21 (approx 6cm) which is the smallest pixel size available.

The quality of the imagery is very high, and for capital city areas, very frequent. Regional coverage is less frequent (3-6 months for Newcastle), & is patchy and one-off for other coastal & inland towns in NSW. Many towns are not covered, or are only photographed in flood time! Some areas I have looked at have more recent coverage on Google or Bing, but usually not as high resolution.

The terms & conditions for the licence say that the first 2 months have unlimited downloads.

 

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Learning about Geography & Geospatial

A MOOC from Penn State

Last week I started Maps & Geospatial Revolution, a Massive Open Online Course from CourseRA. CourseRA delivers varied free courses for universities around the world.

It is a 5 week course. Given the first week took only a couple of hours, you could easily catch up. The quality of the course in both content and execution is so far excellent.

So if you want to learn more about maps and geography within the geospatial revolution then enrol now at CourseRA.