Why is my G-III Map Accuracy not perfect?
I asked Garmin Engineering to comment on, "How accurate should a customer expect his map to be in the new G3?" and "Are the maps in the G3 International Version as accurate as those in the USA?" Here is the response from Garmin Engineering: (10/23/97) =============================================== Joe, We understand that customer expectations are quite high for map accuracy on the GPS-III, perhaps much higher than what the unit was designed to be capable of. Map data in the US is quite complete and fairly accurate, though that is not to say there may not be some minor errors or ommissions in the included data. Map data on the GPS III for areas outside the USA unfortunately will almost always be of less detail and accuracy than in the USA. This is because good quality electronic map data for the USA and to a lesser extent for Canada and Mexico is readily available free or very low cost. Virtually all other countries around the world charge for this type of data, if you can get it at all. We had difficult decisions to make as far as what data to purchase, what to digitize ourselves, and what to leave out. We did the best we could given the cost, and potential customer base to pay for our efforts. For the International mapping data we had to rely on government publications and mapping which were at times dated and may contain inaccuracies and ommissions. Again, we did the best we could given the cost constraints of the unit. Clearly, if the International customer(s) could convince their governmental authorities to make available good quality digitized mapping data for free or a reasonable cost, we would be more than happy to incorporate the data in our base-map. Due to memory constraints, the data is only stored in the unit to a specific level of detail. When the map is zoomed in beyond the stored accuracy of the data, the data is interpolated for display purposes, and OVERZOOM appears on the map to alert the user that the map is displaying interpolated data with reduced accuracy. Naturally, if you examine the position of map features displayed with interpolated data, you will often find roads and other features displaced from their real location. This often happens when straight lines replace curves. The finest zoom scale that we show without indicating OVERZOOM is 3 nautical miles, which represents approximately 250 meters per pixel. If a customer observes an inaccuracy of say 400-500 meters, this represents 2 pixels of error on the minimum useable scale, which should still show you on the road in question, UNLESS the unit is overzoomed and using interpolated data. NOTE: This means that at MAP SCALES BELOW 3 MILES you may observe errors GREATER than 500 meters due to interpolation of map data. A few map sections, particularly in the International Versions, have offsets of several hundred meters. This was a function of the accuracy of the source map data. Again, due to cost constraints on a product of this type, it is not possible to verify the accuracy of individual maps furnished to us. As maps themselves improve, they will be incorporated into our products. Best Regards, Garmin Engineering Olathe, Ks. USA ================================================================ Note from Joe: I just got back from a 1500 mile trip in the Eastern USA with the G3. I found the maps uniformly accurate with just a few exceptions. Considering the VERY limited map memory used, I think most will agree the USA map accuracy is very good. When I was touring Europe earlier this year with MicroSoft AutoRoute 5 (CDROM maps), I noted errors in Europe and the UK in excess of 1000 meters MANY times. MicroSoft's comment on my accuracy findings was much like those of Garmin above. Apparently the USA is very fortunate to have the USGS and related agencies which have done an excellent map making and digitizing job and put their work into the PUBLIC DOMAIN where all of us can use and enjoy these high quality maps. I hope our overseas friends will get on the telephone to their government mapmakers and get all agitated about the lack of inexpensive high accuracy digital maps. This would help all of us in the long run. Joe Mehaffey