I have a set of coordinates data from 3rd party provider. However when I plot those coordinates on google maps with annotations, the annotated points are not exactly on the position they should be. For example, some points should be placed on the road, however they are placed slightly off the road.
My question is, how to solve this kind of discrepancy?
Thanks!
Coordinates (lat and long), by themselves, do not describe a position on the Earth. You need a third piece of information, called the datum. The datum for google maps is WGS84. The datum establishes such things as where 0,0 is on the Earth's surface.
If you've received coordinates, and those coordinates are based on a different datum, then they will not plot correctly on Google Maps.
On the other hand, if the points came from any kind of mobile device (even if it is using WGS84), there are inherent inaccuracies in such measurements (thankfully generally down to < 5m for GPS these days, I believe) that mean that they will not align 100%.
Related
I found this issue while experimenting with shapes. As written in documentation, we can draw circle with radius specified in meters. But Google Maps use cylindrical projection of the Earth (edit: ok, it doesn't), so logically, in Arctic regions our circles should be something similar to ellipse. So I conducted simple experiment and drew a circle near The Egde. That's the result:
As we can see, we still have a circle.
So, my question is, how Google Maps API calculates meters? Is there some constant coefficient between meters and coordinates, used consequently? Or maybe this is a bug and in all other cases one meter in Google Maps equals one meter in reality?
So, as I said in comment, the problem was my misinterpretation of the north edge of the map. When it comes to measuring, Google Maps API is reliable. This is how my 400-meters circle looks like near the real north pole:
Is it possible to determine if a gps point is in water or near(not including elevation) . From what I have seen it doesn't seem possible. I had an idea of somehow getting the gps fence of water bodies and checking if the point lays in the fence. Sounds good but I can't find gps coordinate fences. If any one have any other ideas or a place to get those fences it would be great.
You can get the GPS fence for water from OpenStreetMap.
Then you do a point in polygon operation, optionally you put all polygons in
a spatial search structure, like a quad tree, for a fast polygon search nearby the lat,lon point.
You can start here. and later read more how to identify water in OpenStreetMap
A solution that works on small areas of waters, worldwide, would use much storage space If you concentrate on some countries this should work.
I found that the article is a very interesting approach.
Using google static maps to draw just some pixels around your coordinates, and then check whether its blue or not blue.
You can set a custom unique colour for "water" as a parameter to the google static map, which makes it easy for you to determine if it matches water or not
I'm working on the following scenario: I have a geographical location and I need to create a heat-map visualization of travel times (by car) from that location to anywhere around. I'm planning on using Google Distance Matrix API for getting travel duration. But, since it has a limit on the no of API calls, I need to somehow limit the calls.
My plan, so far, is the following: compute the travel duration (basically a numeric value) to a set of points evenly distributed on a grid around the given position (e.g. 0.5km east, 0.5 km east-0.5km north, 0.5 km east-1 km north etc.). This points would represent the centers of square-shaped areas and I will consider the travel duration to the center as the travel duration to anywhere in the area. Display these areas as colored squares on a Google Maps in a heatmap style.
A good example of something that looks alike is this: http://project.wnyc.org/transit-time/#40.72280,-73.95464,12,709 .
So, my questions are:
Does it seem like a good strategy?
Is there a better visualisation strategy for something like this?
How can I create those square-shaped colored areas on Google Maps?
Thanks!
Calculating duration would surely involve traffic flow rather than simply distance. If your calculations are purely on distance you could use the Google Maps direction requests to calculate the distance to each point.
I'm not sure a heat map is the way forward for this scenario.
There a number of way you could achieve this. Here's a few:
a. Use a custom overlay
(https://developers.google.com/maps/documentation/javascript/examples/overlay-simple)
b. Draw polygons on the map and give them different colours based on
the journey duration. This would involve taking the area in question and slicing it up in to polygons however you need to. These polygons could take the same shape as your example. You would need to be rather precise with your latlng. SQL's spacial querys would help you here depending on the tech your using. (https://developers.google.com/maps/documentation/javascript/examples/polygon-arrays)
c. Depending on how specific you wanted to be you could draw circles with different radius value and different colours.
d. You could make custom markers in the shapes you require and add them to the map in the correct latlng in order to fill an area. You could have different markers for different duration and add them accordingly.
I'm sure there are other options as well.
I have attempted to map some GPS coordinates (longitude / latitude pairs) onto an image of the region of the world that they correspond to. The math was not complicated simply offsetting and then transforming the numbers with a multiplier. However this worked fine for points in Australia, but not for points in New Zealand.
The result is that the points seem to drift south near the middle of the image then slowly correct before the bottom.
Is there some extra math which needs to be taken into consideration for plotting points on a map?
Note:
during my diagnostic excercise I placed my map over google maps and noticed that my version of Australia was different to google maps, but New Zealand was the same as google maps. But the plotting for Australia works but for New Zealand does not.
Longitude/Lattitude is spherical coordinatesystem and will only work if you have a globe to show your map on. In your case you have a flat map and need to project the coordinates onto a flat surface. The maps that Google uses is created with an Mercator-like projection.
What kind of projection you want to use depends on how big area your map consist of. Most countries have their own projection that fit best for their purposes.
Those transformations are quite tricky to work out by hand if your not a mathematician but there are good libraries for transformations like Dotspatial and GDal.
I need to find the width of roads in Google Maps.
Google Earth can't be used as it doesn't support Linux.
Streetviews cannot be used, since it is not available in the area I live.
This link: http://osdir.com/ml/google-maps-js-api-v3/2011-05/msg00666.html suggests the method of finding the distance between the two ends of the road by knowing the coordinates of both sides.
Therefore the first question is as in title.
BTW, I have managed to display the "route" between the two coordinates already on the maps.
The type of the map can be set to "satellite" view through the API.
Does that affect the distance and coordinates that'll be fetched?
All this stuff about getting points across the street from each other is further complicated by the fact that sometimes the geocode returned will be a ROOFTOP geocode--likely meaning the centroid of a building--and other times, it is RANGE_INTERPOLATED which suggests that it will be not very precise. See http://code.google.com/apis/maps/documentation/javascript/reference.html#GeocoderLocationType. In either case, it won't be the edge of the road.
It may be sobering to look just how far from the road Google Maps may put the marker for an address: http://maps.google.com/maps?f=q&source=s_q&hl=en&geocode=&q=4+Clinton+Drive,+Englishtown,+NJ&aq=&sll=40.299985,-74.290066&sspn=0.009426,0.015213&gl=us&ie=UTF8&hq=&hnear=4+Clinton+Dr,+Englishtown,+New+Jersey+07726&t=h&z=16
In short, unless your use case can tolerate a pretty wide error bar, I think it's safe to say that this just isn't going to work, at least not without considerable resources at your disposal.
Google Earth web plug-in is not available for Linux, but if you don't need it to be a web page, then you can try working with Google Earth app, perhaps. It works on Linux.
If your use case is for a reasonably narrow geographical area, there may be data available elsewhere. But getting this from Google Maps API v3 is unlikely to be a very good option.
(As always when I give a "I don't think this is feasible" answer, I'd be happy for someone to come along and prove me wrong.)
I'd look at the coordinates of individual houses. If house numbers are arranged such that n+1 is on another side than n, the distance between the two might tell you something about the width. But I don't think there's an API for that...
Here's the NON API solution i thought of,
In my country , roads named with different code names like "A3" , "B354", "C6".
"A" is for main roads. Most of the time width of the road is consistent as per road code. Therefore we can use road code to get the width of the road. I don't know if this works for your country.