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12 January 2012

Downloading Nearmap Imagery for GIS and CAD Use



There are two protocols that Nearmap clients can use. The first is the Tiled Map Service (TMS), which you can use if your GIS application supports this (ArcGIS, Mapinfo and alike). The second service the Web Map Service (WMS) that supports most GIS applications and is only available to paid clients. I prefer the TMS protocol as it is not only free but you are able to load the tiles that you need from the Nearmap servers rather than mass importing which wastes bandwidth and time.



HyperTiles
If you do not have a fancy GIS application, Nearmap have developed a Windows (damn, no Mac version) based application called HyperTiles that allows you to download the latest (or from a specific date) aerial photography and save it as a georeferenced .jpg file. When you select the area of interest you will be prompted to select the resolution you want to download, it will also give you an estimated download size. Then HyperTiles will download the individual tiles (from the TMS) and it will form one large image.



Size and Limitations
There is no limit to the size of the area you want to download but if you select the whole of South East Queensland for example, expect that you will be downloading Gigabytes and simply the size of the image would probably crash your GIS or photoviewer program.


If the output size of the selected region, at the chosen resolution, is larger than the maximum tile size then the selected area will be subdivided into multiple tiles. This is indicated by the grid that is drawn on the preview image.

  1. The selected region is output as a series of tiles that fully cover the region.
  2. A georeferencing world file (JPW) is saved with each tile.
  3. The tiles are saved in a subdirectory with the specified name in the selected output path.
Another little trick is that you can zoom to the maximum extent and you can see tell what areas have Nearmap coverage as the areas are opaque. Currently Nearmap covers ~75% of the population, but keep in mind we are coastal dwelling so much of Australia is not covered.   

Screenshot and Conversions
The other dodgy option is to take a screenshot (Print Sc), but you are taking that photo at screen resolution. So what you see is what you get. HyperTiles allows you to zoom to a particular height, then you are able to select the resolution that you want to download. HypeTiles also gives you the option to import a .KML file which can be easily generated using the shp to kml or gpx to kml conversion in ArcGIS. 

Layers
HyperTiles has the ability to show in conjunction with the PhotoMap layer a:

StreetMap layer
Terrain layer (Digital Elevation Model)

I found that overlaying a TerrainMap and set transparency onto a PhotoMap give your image tremendous depth and elevation. 

Datums / Coordinate Systems
There are a number of coordinate systems that can be set to your output image. However, most GIS applications will allow you to convert the coordinate system to whatever you need (I.e. ArcCatalog)

WGS84 Spherical Mercator
GDA94 Geodetic
WGS84 Geodetic
GDA94 MGA Zone 49
GDA94 MGA Zone 50
GDA94 MGA Zone 51
GDA94 MGA Zone 52
GDA94 MGA Zone 53
GDA94 MGA Zone 54
GDA94 MGA Zone 55
GDA94 MGA Zone 56

Post Processing and Merging Tiles

HyperTiles has the ability to run a "post processing" command after a save has completed. An example is included that demonstrates how to use GDAL to mosaic and compress the saved tiles into a single GeoTiff or ECW. This can be setup as follows:

Download GDAL binaries release-1500-gdal-1-7-mapserver-5-6.zip  


Extract the downloaded zip file to somewhere on your computer

Edit the "GDALCompress.bat" file, that is located where you installed HyperTiles ( e.g. "C:\Program Files\NearMap\HyperTiles" ), and set the GDAL_DIR to the location where you previously extracted the GDAL binaries.

Run HyperTiles and enable post processing in the options.

Do a save of a small test area to make sure that the GDAL integration is working correctly.

The instructions above explain how to use the HyperTiles Post Processing functionality to mosaic tiles using GDAL. Alternatively you could use a GIS image processing package, such as ERDAS ER Mapper. HyperTiles creates ERS headers files for each jpeg tile so they can easily be used by ER Mapper.

2 comments:

  1. Update: Nearmap (and Hypertiles) no longer free
    As of February 2013, Ipernica (the new owner of Nearmap) is charging for access to Nearmap and Hypertiles. The MINIMUM cost is over $6000 per year. For most users, this puts the product completely out of reach. Here's hoping they come to their senses before they go bankrupt and we lose the product completely.

    ReplyDelete
  2. Thank you for letting us know. This is just awful. When I was on placement at TransLink they were using it for free despite being an organisation. Hopefully institutions are forced to pay for a government or industrial licence, then I am sure it can be both profitable and accessible to average joe.

    ReplyDelete

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