Manifold Community Site: Projection trouble though I have datum and spatial extent

RE: Projection trouble though I have datum and spatial extent

Kris Austral — Tue, 26 Aug 2008 18:39:07 GMT

Hi, another annoying newbie question (I do read and re-read the manual, but it's obviously not sinking in!)

I have a .shp file showing areas across a whole state. It's from a government department (who generally use AGD 94 as the datum), and has a little blurb saying: SPATIAL EXTENT N Lat -28.0, W Long: 141.0, S Lat: -37.5, E Long: 154.0.

In Edit - Assign Projection, AGD 94 is automatically accepted. If I just press OK, the image has latitude and longitude displayed onscreen as within the bounds provided for the Spatial Extent. However, when I opened the image in Google Earth (.kml) to see how that function worked, the areas failed to correspond to the city features they were meant to be centred on (being about 200 km north).

So, I started again, tried Edit-Assign Projection, kept AGD 94, and also checked Orthographic and "Suggest", getting Centre Latitude: -32 and Centre Longitude: 147, which seem right. But the latitude/longitude displayed onscreen is then about 3 degrees out of the Spatial Extent provided, and opens in Google Earth as a teeny tiny area about 8m wide in the middle of the state.

I'm probably trying to do too much too fast but need australian examples to show my boss. Any help would be really appreciated.

Cheers

RE: Projection trouble though I have datum and spatial extent

ColinD — Tue, 26 Aug 2008 18:50:43 GMT

When you open the newly imported shapefile what coordinates show in the info bar at the bottom of the window? I'm guessing that for the whole state they are going to show lat/lon, in which case you would assign projection to Standard, Lat/Lon, GDA94. You would need to give more detail as to what you are doing next to show in Google Earth.

RE: Projection trouble though I have datum and spatial extent

Kris Austral — Tue, 26 Aug 2008 19:08:18 GMT

Hi,

In the bottom of the window immediately after importing and opening the .shp drawing is Latitude/Longitude 164(degrees)54.056' E 23(degrees)59.413'S

RE: Projection trouble though I have datum and spatial extent

Graeme — Tue, 26 Aug 2008 19:22:39 GMT

Hi Kris, you refer to both a shapefile (drawing) then an image which you describe as a .kml . What are you trying to achieve? Do you have any other reference data to check your initially imported shapefile drawing against? There shouldn't be a significant difference between an unprojected (lat/long) drawing using GDA94 datum and WGS1984auto (default for Google Earth). Maybe post a sample of the data and/or the project with just defaults for the shapefile after import.

RE: Projection trouble though I have datum and spatial extent

Kris Austral — Tue, 26 Aug 2008 20:37:10 GMT

Hi Graeme,

Sorry, I'm not being very clear. I've only had Manifold for about a week, and don't have much of a reference library built up yet, so I thought comparing it against Google Earth would be a good way of checking everything was OK. Plus it's been a nifty way of showing Manifold to the boss. (Other shapefiles from different sources have imported into Google Earth as .kml and aligned perfectly with existing landmarks/railways etc).

I have a shapefile of native title claim areas in the state of NSW. I can play with it in Manifold with no trouble. It opens with GDA94 Datum and I thought all was fine.

Then, I was doing the Export Drawing to Google Earth exercise in the help file, and thought it would be cool to use some Australian data. So, I exported the shapefile drawing as a .kml into Google Earth, just to see what it would look like.

However, using the Projection of Standard/LatLong/GDA94, the image doesn't overlay properly onto the state of NSW as shown in Google Earth. It's too far to the north (so the native title claim areas that should be centred on Sydney are instead way up on the coast near the border) and some of the areas aren't displaying properly (the are outline only, instead of filled areas, or flicker on and off).

So, I thought I had projected the image incorrectly, and am wondering how to fix it.

RE: Projection trouble though I have datum and spatial extent

Graeme — Tue, 26 Aug 2008 22:28:19 GMT

OK Kris, there are two paths for exporting to kml. One is right click the drawing in the project pane and invoke the export dialogue; the second is with a map window open, choose file / export / drawing. If your map component started life with an image, it could be that the exported kml inherits the projection details of the map component including offsets and scale. That may be the problem. Try right clicking the drawing's tab in the map window and choose "use projection", that will set the maps native coordinate system to that of the drawing, then try file / export again (you may loose visibility of any linked compressed images, but they probably shouldn't be in the map given what you're trying to do).

We routinely export lat/long data of NSW to KML and don't have a problem - they display fine in GE, so it is almost certainly something you haven't actively controlled at the map window end.

It is also possible you have tried to assign the projection more than once, rather than confirming it is correct in the first place, then using change projection - most of us have been caught by that one at some point.

If you are unable to post some data or an unworked map file containing freshly imported data, it will be hard to help pin it down.

RE: Projection trouble though I have datum and spatial extent

ColinD — Tue, 26 Aug 2008 22:28:31 GMT

Maybe the data is not in the projection you think? I have just exported to kml some NSW state-wide polygons in lat/lon and they locate in the correct place in GE. Do you have a link to the data you are trying?