View Full Version : gps for deisgn work
Richard on Maui
07-05-2006, 04:27 PM
Has anyone used a gps for doing design work? I am wondering if you can buy affordable ones that will be accurate enough for say, plotting swales? Or locating features such as trees and trails and structures and so on on maps?
I am kind of challenged when it comes to sketching maps out to anything like an accurate scale, which makes the process of designing sort of hard :(
Any thoughts appreciated...
07-05-2006, 04:33 PM
hey richard....you could try Darren Doughety's site to get some info. He uses a program for his computer, costs quite a bit I seem to remember him saying, but he may be able to help out in some way.
08-05-2006, 10:09 AM
Richard do you know anyone with a small plane? Most pilots these days have a small GPS unit and many like ours are mobile...we take it in the car and the plane. It's a Garmin....dont know the numbers that go with it.
Chris has used it to locate survey points on our place but don't know about swales and stuff.
Richard on Maui
08-05-2006, 11:23 AM
Thanks Kathleen and Cathy,
You know if I knew someone with a plane I might just get them to do a few low fligh overs of the property and take a bunch of digital photo's and go from there. Could possibly just superimpose them on a map with transparencies and get a pretty good indication of where a lot features are...
I think I will email Darren, and see if he will reply to this thread.
My suspicion is that to get very good accuracy at all is beyond the scope of the gps units you can get for under $500.
08-05-2006, 01:13 PM
Richard, I think the GPS's now are super accurate. I think a lot of the reasons for accuracies is regional. Most of the GPS satellites are military and some areas are 'sensitive'.
Any local afficionados should be able to give you an idea of accuracy, I think most coverage now is down to 1/2 metre accuracy. This should be accurate enough for swales.
I am contacting a friend who knows more about these things. I have a mobile GPS on my workboat which I can sorta use. If I get anything more exact I will post it here.
09-05-2006, 02:20 PM
Here is a link to a fun sport called 'geocaching'. It also gives 'us mugs' good into on GPS units.
Here is the page on benchmarks, you should be able to check your GPS and its accuracy by linking to a couple of local benchmarks.
Richard on Maui
09-05-2006, 03:50 PM
Thanks for that floot. I don't have a gps yet. I am sort of trying to find out if one would be worthwhile for the purposes of mapping out the property I am working on before I spend the money...
Sounds like they are pretty accurate. 1/2 metre would be accurate enough for placing trees I guess, although, I would want more accuracy for making swales... although I guess I should withhold my judgement until I give it a go.
09-05-2006, 05:01 PM
I was also hoping to use a GPS to speed up the surveying of my block as I already do a fair bit of digital mapping and geospatial nerd-work. However unless you have big dollars to spend :cry: or are working on fairly broad scales the best option still seems to be tape measures and laser levels.
As for GPS; specifications can change a bit depending on your location, topography etc. but here in Aus your standard 12 channel GPS unit is typically accurate to within about 10 meters.
Many new units also have WAAS (Wide Area Augmentation System) which can increase the locational accuracy to better than 3 meters but currently WAAS is only available in North America so you would need to check if it available there in Maui.
GPS units that boast sub-meter accuracy are used in surveying work in conjunction with ground based repeater stations or subscription services to geostationary satellites and would set you back a minimum of $5000.
The mapping software can be very expensive but there are several cheaper (and easier) programs that you can use to overlay GPS points with topographic maps or aerial photos. However some of the cheaper programs don't handle GPS data with the same level of accuracy (such as a ten meter minimum mapping unit) as the better programs.
I hope thats of some help to you :?
09-05-2006, 06:52 PM
I just got 10mins of techno mumbo jumbo from my husband (Chris) about the GPS for mapping ground features but I think the message was GPS is accurate if used with a theodolight?? also our place was roughly mapped with GPS co-ordinates and when surveyed some of the fence lines were 30 meters out. Also the shadow a plane casts at 3,000 feet is the same size shadow as when the plane is 30,000 feet. chris assures me this point is very relevant to ground mapping with GPS.
Going to get a panadol now for my headache
Richard on Maui
10-05-2006, 11:01 AM
Ha Ha. My head hurts when I try to use a tape measure so maybe I should stay away from the more sophisticated kine. Especially at $5000... Well, back to the old tape measure and note pad. (Last feww times I set out I got distracted by weeds, or runaway goats or chickens or whatever, ended up putting the notebook down and only remembering it after the rains had destroyed all my notes. Wouldn't be so bad if it hadn't happened more than once. Yes, that's right I am a mess.
That's interesting about the shadows of an airplane. Woulda thunk they would be bigger the closer the plane is to the earth...
11-05-2006, 03:51 PM
Ha Ha. That's interesting about the shadows of an airplane. Woulda thunk they would be bigger the closer the plane is to the earth...
Yes me too. Maybe its because the altitude of the plane is insignificant compared to the distance from the sun. :?
Would you care to give us a detailed explanation Cathy? :lol: :wink:
12-05-2006, 06:57 AM
Here is something a bit more explanatory on GPS accuracy. I went looking because I have a staff member I mentioned this to and he explained the GPS gear he used on farm tractors was accurate to 1 centimetre on any axis. He also said that in time of war this could blow out to anything up to 1km.
Maybe you could hire one of the flash models get it home and run like hell all over the property. :shock: :oops:
My staffer, B, is an interesting guy. A commercial pilot who speaks, apart from english, fluent french & swahili, telephone standard arabic, afrikaans & mandarin and can get by in a few others. Yes, I am very lucky to have him around. I have yet to ask him about the 'shadow' thing.
Richard on Maui
12-05-2006, 04:21 PM
Aha! okay, cm's... that'd work. I wonder if I could borrow your pilot for a week? Would he like a little holiday in Maui?
12-05-2006, 07:07 PM
Yep Little Fish gets the gong.....the distance between the plane and the earth is insignificant in relation to the distance between the earth and the sun, which is where shadows come from.
I thought he knew this from great studies in meteorology but it was on John Laws Useless Infomation .... (he is Australia's most famous radio talk back host)
22-08-2008, 06:34 AM
So I'm doing some initial mapping of a 35 acre piece of land on the Toutle river, http://twistedhazelsorchard.googlepages.com/home, and have been playing around with all kinds of mapping programs, gps tools, and basically anything that would keep me from running around this somewhat large dense thicket of forest land with a long measuring tape and sight level. My current goals of this initial map are: identify plant communities, trails/roads, property lines, soil types, major features, and basic map for design work. When I get to the dam and swale phase I'm sure I'll be renting the ol' laser level and such. As fun as that will be, it seems like a gps and google earth will get us what we're looking for at a minimal cost. We've avoided subscribing to google earth plus because it won't interface with our holux m241, nor would it export a track to the gps(kind of lame).
The process we've currently developed:
1. Take our small holux m241 GPS device to record tracks and waypoints
2. download them onto my computer using BT747 and save them as a KML file (google earth language)
*This program will access the kind of GPS chip our holux device has, MTK, and offers us interfaces to it that the very basic device doesn't offer. It also allows us to download the tracks AND waypoints and converts it into KML. BUT it's not so user friendly, it took our programmer a couple hours to figure out the finiky glitches of the program. As a non-programer I wouldn't have been able to operate the program. If anyone has a more user friendly free program to download tracks and waypoints i'd love to check it out.
3. Open the KML file in google earth. Our initial playing around has found that our GPS has about a 5' accuracy.
Then i use google earth tools to make polygons or paths to overlay over the imported GPS data. I find that the native google earth tools are easier to make changes to then the imported tracks and waypoints. We've also import and added as an overlay a free topographic map my county has provided that has 20' contours: http://www.co.cowlitz.wa.us/gis/atlas.html
Then print from Selected Folder in My places, which i've arranged to print all the plant communities i've polygoned, etc. So this has been the low-tech mapping we've been playing around with.
So, anyone have advise for a better way to import tracks and waypoints into google earth or have another free mapping program you prefer?
Importing the tracks and waypoints into google earth seems to be working, but using it's polygon tools seems a little clumpsy. Does anyone have advise on a better program to import these maps into for a more interactive landscaping type program that would give more tools and keep the topo overlay and google earth satellite imagery?
Ahh the skies have opened. Time to pick blackberries!!
Thanks for any feedback.
22-08-2008, 10:58 AM
If you want Google Earth's images unfortunately you have to work within Google Earth.
You could also try ESRI's ARC GIS Explorer which has its own image collection which is supposed to be pretty good for the continental US; rubbish for anywhere else in the world (sigh).
Otherwise Quantum GIS (just google for "QGIS") is a freeware mapping program that is a bit more sophisticated than google earth but you'll need to access images from somewhere - try your local government Lands Office for Aerial Photography.
08-12-2008, 02:10 PM
I would love to learn more about mapping and don't really even understand what GIS is...
I've played around with Google Earth, but have had better luck and more updated photos with our county tax maps (Georgia, USA).
I have done one design so far for a couple, and used the county tax map, and a topo map I found on line.
That was good enough to make a design.
We have a 41 acre site with only about 30' of drop from one end to the other, that we are working on (and will be working on forever I think!) and I am wondering with our site how to go about mapping it more in detail, to know exactly were all of the gullies, hills etc. are. The biggest problem is that the whole piece is densely covered in trees, so it's very hard to measure or even use a laser level. (We made one from a laser pen and level.) I've just been pacing it out, and using a compass...
Anyone have any ideas for anything that will be sharper than Google, short of mowing down all the trees?
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