Differences

This shows you the differences between two versions of the page.

--- braindump [2018/04/17 22:00] – [Ellipsoids] allchin09
+++ braindump [2021/03/07 22:02] – [Topographic maps] allchin09
@@ Line 27: / Line 27: @@
 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 =====
@@ Line 55: / Line 64: @@
 ===== Topographic maps =====
-  * 1:63360 (2 inch:mile)
+  * 1:63360 (1 inch:mile)
     * 1st edition
     * 2nd edition (not all were revised
     * Note that the maps don't cover the whole of the state, they are mostly focused towards the coast. Also, there are a few 'holes' (eg Burragorang) where maps towards the coast were not published. This information is based on an index map held in the SLNSW which indicates which maps are in their collection, and it is assumed that they hold all maps which were published.
-  * 1:31680 (1 inch:mile)
+  * 1:31680 (2 inch:mile)
   * 1:50000 Army/RASC
     * 1st edition (ANG)
@@ Line 91: / Line 100: @@
     * Elevation Data
       * [[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 ======
@@ Line 128: / Line 142: @@
 ==== 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) ====
@@ Line 138: / Line 152: @@
 [[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 =====
@@ Line 166: / Line 180: @@
 ===== 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) =====
@@ Line 183: / Line 200: @@
 ^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 |
 ^Used in                | ANG           | AGD, AMG | GDA, MGA    | GPS         |