GPS for plant locating

[poschiavanus]

A few quick points:

Google Mapmaker with GoogleEarth is unlikely to give you a resolution better than a current consumer GPS (say 5 m for isolated readings, and 2-3 m for repeated readings for the same location. Also if you create maps in Google MapMaker, Google places some ownership and other constraints on how you can use the data, particularly if you use GoogleEarth as the source: read the Google license & associated T&Cs carefully to check that what you want to do does not conflict with these.

Other Products. There are a number of other products which are free to use which can be used for drawing maps. I would suggest looking at Quantum GIS, which is a relatively straightforward product. These do not impose any restrictions on how you use the data (in the jargon: they are both "free as in beer" and "free as in speech".

Ordnance Survey OpenSpace data may be a good place to start if you want to build a map. There is vector data (lines and areas) for things like roads, woodland, water bodies; and raster (picture) data at around 1:12000 scale (the StreetView layer) which can be used as a base.

The best way to be able to return to specific plant locations is to a) locate them with a GPS, and b) relate them to several features readily locatable at that GPS location. e.g., five paces between the large oak and the ash sapling. Try and use features which may exist in 20 years time! A photograph of the general location with the desired location indicated is a good way of achieving this. It takes practice, and I'm still learning the ropes.

HTH,

Posch

[Meta menardi]

Some interesting stuff there, I shall certainly check out Quantum GIS, a quick scan of their site looks very interesting.

I do take your point about surveying in points of interest, it is just so hard to know what will last. More than once I have found that the notes and so on given to me refer to the corner of a building that has gone, a power pole that is no longer there and a measurement across a site from corner to corner that is 15m larger on the plan than it is on the ground. Careful choice helps, but isn't always foolproof.

[Johnny Redgate]

Originally Posted by Meta menardi

Try Mapmaker, there is a tutorial on the site that shows you how to use it with Google Earth. I have never used it for a serious job, but it looks quite useful.

I've just tried using this for a current project. The tutorial I think you refer to tells you how to convert Google Earth .kml files into ESRI shape files via a free download programme DNR Garmin. Unfortunately I couldn't get this to work, and this may be due to the current version of Google Earth changing the .kml files a bit (details on Mapmaker website I think).

However, Mapmaker has a utility to directly import .kml files and create shape files which looks very useful. Unfortunately it is only available on Mapmaker Pro i.e. the full program you have to pay for. You can however download a 30 day evaluation copy for free which then reverts to the cut down free verion (without the above utility) after the evaluation period is up.

Does Quantum GIS import .kml files and does anyone know if cheap graphics tablets can be used to draw polygons in Google Earth?

[poschiavanus]

The simplest way to convert KML files between formats is GPSBabel (you may find a copy in the GoogleEarth directory).

AFAIK qGIS will import GPX format files. There is a utility package called ogr2ogr incorporated with qGIS which does lots of other things, but it may be tricky to run on Windows.

[Meta menardi]

Originally Posted by Johnny Redgate

does anyone know if cheap graphics tablets can be used to draw polygons in Google Earth?

The biggest problem with using graphics tablets is calibrating them to the correct scale, as soon as you zoom, you have to re-calibrate. Geo-registering raster files can be quite successful, but it does depend how your GIS deals with rasters. I did a job recently were I was able to scan a large number of site plans on an A0 scanner, overlay them onto OS landline data and digitise the site data to a vector layer. Very easy way to work, but I wouldn't like to do it on some GIS systems.

[Johnny Redgate]

Hmmm. I have habitat surveys for large and complex urban mosaics that I have mapped onto Google Earth images in the field. What I would like to be able to do is find a quick way of drawing polygons as accurately as possible in Google Earth and then transfer them to my site base baps (which are very very blank!) on GIS (Mapinfo but can import shape files). I know I can do this by scanning the field maps and registering the images but drawing polygons directly in GE means I can keep zooming in and use all the resolution available where necessary. Unfortunately there is no snap function, the drawn boundaries only approximate to the map boundaries because of things like tree canopy spread obscuring hedges and fences, and because I find it difficult to draw free hand with the mouse. Therefore I would have to re-digitise the GE polygons in Mapinfo to get it all to fit together nicely, but they would be accurately positioned on the map base. I would therefore need to draw polygons quickly in GE and so I thought a graphics tablet and pen would help, but it seems not. If no-one has any better ideas I guess I'm back to scanning and registering field maps?

[Hobjob]

I replied to this thread via my phone last week-end, but it seems to have got lost - no doubt my fault.

Google maps are accurate and usable to about 1-3 feet.
It is a bit clunky though.

Take a GPS reading when out, with notes and hopefully location photos.

Back home put the readings into google maps at max resolution (not street view).
Now as accurate as you can right click the tip of the arrow cursor on the spot you want. Choose "Centre map here'.

Now paste this bit of arcane Java script into the address bar of your browser
(not the search bar of google maps) and hit enter.

javascript:void(prompt('',gApplication.getMap().ge tCenter()));

This will give you decimal lat and long to silly amounts of decimal poiints for the centre of the maps.

I can easily differentiate between the edge, middle and opposite edge of my roof solar heating.