- Managing DEMs
- Topographic maps
- Mobile apps
This is an old revision of the document!
Talk to LPI about their plans for topographic mapping in NSW
NSW Government is investigating the possibility of privatising LPI. Possibility of breaking the organisation down into branches. Need to investigate what the impact on mapping and access to spatial data may be.
Update - 08 Jun 2016
It appears as though LPI will be broken down into three entities, with Titling and Registry Services (TRS) section of LPI privatised.
Thankfully Spatial Services, the entity relevant for mapping and spatial data, seems set to stay under public ownership.
However, the mapping section has already be moved from Prince Albert Rd Sydney, out to Bathurst. No longer can one walk into an LPI building in Sydney to make mapping related enquiries, or to look at aerial images through a set of stereo glasses.
See http://www.ga.gov.au/scientific-topics/positioning-navigation/geodesy/geodetic-datums for more information on relevant datums for Australia.
[Brief explanation of datums. Possibly include a “datum vs projection - what's the difference?” section.]
Reference co-ordinate system used for GPS (Global Positioning System)
WGS84 Bounds: -180.0000, -90.0000, 180.0000, 90.0000
Projected Bounds: -180.0000, -90.0000, 180.0000, 90.0000
Scope: Horizontal component of 3D system. Used by the GPS satellite navigation system and for NATO military geodetic surveying.
GDA94 is the Australian representation of WGS84. There is almost no difference in a 2d sense (Australia has a separate height datum), at least from a bushwalking perspective.
WGS84 Bounds: 108.0000, -45.0000, 155.0000, -10.0000
Scope: Geodetic survey.
Area: Australia - all states
The datum used on topographic maps before GDA94. 2nd Edition topographic maps use the AMG66 projection which is derived from AGD66.
Prior to 1966 the ANG was used, which covers both the 1:63360 and 1:31680 maps topographic maps.
The ANG makes use of the Clarke 1858 spheroid.
Conversion tool by Anthony Dunk - http://www.binaryearth.net/AusDatumTool/index.php
See http://spatialservices.finance.nsw.gov.au/surveying/geodesy/projections for more information on relevant map projections within NSW.
There are three UTM projections of GDA94 relevant to NSW.
Used by NSW GIS systems for whole of state projections.
WGS84 Bounds: 141.0000, -37.5000, 153.6200, -28.1500
Projected Bounds: 8709235.6860, 4009911.3943, 9951732.0554, 5048642.3129
Scope: Natural Resources mapping of whole State.
Area: Australia - New South Wales (NSW)
Used in many popular web mapping applications (Google/Bing/OpenStreetMap). Uses spherical development of ellipsoidal coordinates. Relative to an ellipsoidal development errors of up to 800 meters in position and 0.7 percent in scale may arise. It is not a recognized geodetic system: see WGS 84 / World Mercator (CRS code 3395).
The international standard projection coordinate system. The parameters of MGA are identical to that of UTM, except that they differ in spheroid (GRS80 vs WGS84)
An ellipsoid (sometimes referred to as a spheroid) is a simplified mathematic representation of the Earths shape. A spheroid can be defined by two parameters, typically: the semi-major axis (alpha) and the inverse flattening (1/f)
The below table summarises relevant values for common spheroids.
|Major Semi Axis||6378293.645||6378160||6378137||6378137|
|Used in||ANG||AGD, AMG||GDA, MGA||GPS|
Further information on geodesy can be found here - myGeodesy
In the geographical context, the prominence of a mountain is the elevation differential between the mountain’s summit elevation and its highest pass/saddle connecting it to its parent.
It is of use to bushwalkers as it provides an indication of relative difficulty in the effort required to reach a peak. By applying among other things a prominence criteria, a list of peaks that meet that criteria can be complied. An example is The Abels of Tasmania, where only peaks over 1100m altitude but with a prominence greater than 150m are included.
The prominence criteria is important as it removes high peaks that are near to each other in altitude and would require little elevation gain to travel between them.