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braindump [2016/08/21 06:00]
allchin09 [Ellipsoids]
braindump [2018/10/10 10:33]
allchin09 [Australian National Grid (ANG)]
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 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. 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.
 +
 +==== Half of NSW topographic maps no longer printed ====
 +From 3rd September 2018, 524 out of their 1,094 titles for the state were only made available in digital form from Spatial Services. By area, this covered about 3/4 of the state.
 +
 +A notice regarding the change can be found [[http://​spatialservices.finance.nsw.gov.au/​__data/​assets/​pdf_file/​0008/​219455/​SpatialServices_Topoletter.pdf|here]]
 +
 +[[http://​maps.ozultimate.com/?​id=1534338535930|Interactive map of '​digital only' maps]]
 +
 +{{ ::​digitalonlymaps.jpg |}}
 ===== Geographic Names Board ===== ===== Geographic Names Board =====
  
-  * why are co-ordinates ​only accurate to the nearest minute in AGD66 co-ordinates?​ 1 minute is around 1.1km of latitude, and 0.93km of longitude (around Sydney). This means that the accuracy is presumably limited to half of that, or say +/-500m in each direction. For example, Mt Cloudmaker is around 500m from its correct position+  * why are coordinates ​only accurate to the nearest minute in AGD66 co-ordinates?​ 1 minute is around 1.1km of latitude, and 0.93km of longitude (around Sydney). This means that the accuracy is presumably limited to half of that, or say +/-500m in each direction. For example, Mt Cloudmaker is around 500m from its correct position
  
-  * Spoke with GNB Secretariat (Susan Fietz - susan.fietz@lpi.nsw.gov.au) on the matter (27 April 2016):+  * AA spoke with GNB Secretariat (Susan Fietz - susan.fietz@lpi.nsw.gov.au) on the matter (27 April 2016):
     * What is on the GNB website is the official name places list     * What is on the GNB website is the official name places list
     * Updating of the list planned to start within the next few years     * Updating of the list planned to start within the next few years
     * Any corrections are welcome     * Any corrections are welcome
 +
 +  * AA spoke with the Surveyor General (Narelle Underwood) on the matter (Jan 2017):
 +    * Acknowledged that the current system has its flaws are requires upgrading
 +    * Work is going to be done (timeframe not specified) on "​bringing the GNR (Geographic Names Regester) into the 21st century
 +    * Many errors in the listed coordinates are due to the location being recorded in lat/long to the nearest minute but in the top left corner of the grid square, as opposed to the bottom left as convention dictates.
 +
 +  * AA spoke with staff member from GNB on the matter (Apr 2018):
 +    * Acknowledged the issue and the plans for a project to address it
 +    * No funding available in the current political climate
  
 ====== Licensing ====== ====== Licensing ======
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     * Elevation Data     * Elevation Data
       * [[http://​www.ga.gov.au/​elvis/​|ELVIS - Elevation Information System]]       * [[http://​www.ga.gov.au/​elvis/​|ELVIS - Elevation Information System]]
 +
 +====== Terminology ======
 +Well defined and consistant terminology goes a long way to assist in clear and well understood communication.
 +
 +Refer to the [[terminology]] page for further information.
  
 ====== Datums ====== ====== Datums ======
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 ==== AGD66 ==== ==== AGD66 ====
  
-The datum used on topographic maps before GDA94. 2nd Edition topographic maps use the AMG66 projection which is derived from AGD66.+The datum used on topographic maps before GDA94. ​1st and 2nd Edition topographic maps use the AMG66 projection which is derived from AGD66.
  
 ==== Australian National Grid (ANG) ==== ==== Australian National Grid (ANG) ====
Line 129: Line 152:
 [[http://​www.binaryearth.net/​AusDatumTool/​AustralianNationalGrid.html]] [[http://​www.binaryearth.net/​AusDatumTool/​AustralianNationalGrid.html]]
  
-The ANG makes use of the Clarke 1858 spheroid.+The ANG makes use of the Clarke 1858 spheroid, where the parameters are expressed in British feet for mainland Australia (and Clarkes feet for Tasmania).
 ===== Datum Conversions ===== ===== Datum Conversions =====
  
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 ===== Web Mercator (EPSG:​3857/​EPSG:​900913) ===== ===== Web Mercator (EPSG:​3857/​EPSG:​900913) =====
  
-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).+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 40 km may arise. It is not a recognized geodetic system: see WGS 84 / World Mercator (CRS code 3395). 
 + 
 +For details on the issues using Web Mercator for geospatial applications,​ see the report from the US NGA (National Geospatial-Intelligence Agency) on [[http://​earth-info.nga.mil/​GandG/​wgs84/​web_mercator/​(U)%20NGA_SIG_0011_1.0.0_WEBMERC.pdf|Implementation Practice 
 +Web Mercator Map Projection]]
  
 ===== Universal Transverse Mecator (UTM) ===== ===== Universal Transverse Mecator (UTM) =====
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 ^Parameter ​             ^ Clarke 1858   ^ ANS      ^ GRS80       ^ WGS84       ​| ​ ^Parameter ​             ^ Clarke 1858   ^ ANS      ^ GRS80       ^ WGS84       ​| ​
-^Major Semi Axis        | 6378293.645 ​  | 6378160 ​ | 6378137 ​    | 6378137 ​    |+^Major Semi Axis (m)    ​| 6378293.645 ​  | 6378160 ​ | 6378137 ​    | 6378137 ​    |
 ^Inverse Flattening ​    | 294.26 ​       | 298.25 ​  | 298.2572221 | 298.2572236 | ^Inverse Flattening ​    | 294.26 ​       | 298.25 ​  | 298.2572221 | 298.2572236 |
 ^Used in                | ANG           | AGD, AMG | GDA, MGA    | GPS         | ^Used in                | ANG           | AGD, AMG | GDA, MGA    | GPS         |
  
-Further information on geodesy can be found here - [[www.mygeodesy.id.au | myGeodesy]] ​+Further information on geodesy can be found here - [[https://www.mygeodesy.id.au | myGeodesy]] ​ 
 + 
 +====== Prominence ====== 
 + 
 +===== What is it? ===== 
 + 
 +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.// 
 + 
 +[[http://​www.surgent.net/​highpoints/​prominence.html]] 
 + 
 +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. 
 + 
 +===== How is it calculated? ===== 
 + 
 +[[https://​en.wikipedia.org/​wiki/​Topographic_prominence]] 
 + 
 +[[https://​github.com/​edwardearl/​winprom/​|WinProm - a computer program]] 
braindump.txt · Last modified: 2018/10/10 10:33 by allchin09