Forum: General Topics
Forums / General Topics / Fine Tuning Map Alignment.
| Subject: | Fine Tuning Map Alignment. | |
ChrisM 10:54 Location: Phone Model: | Hi Stephen, In Map Organiser, it is not always that easy to get the exact N & E coordinates out of whatever program/website the map is coming from. Often I can be a bit out of alignment and on a small scale (detailed) map this error can sometimes be quite significant. Now I know that you can fine tune the alignment in the TMJ application. How does this actually actually work? Do you record an offset to be used for that specific map file? If so, it might be useful if there was some way of feeding this back to Map Organiser and adjust the coordinates accordingly... (or something like that) Does this make sense? Regards, Chris. | |
Stephen 13:42 Location: Phone Model: | Hi Chris, The re-calibrate function on the TMJ map page is pretty crude to be honest. All it does is shift the entire map a preset amount of pixels in the X and Y direction, set when you select Re-Align to Current Location. To set it you just need to scroll the map so that your *actual* location is centred, then select Re-Align... It then just stores the pixel offset from the displayed location to the actual location. This wouldn't really help in realigning the map in the Map Organiser, since each coordinate would have to be out by exactly the same amount for this to work (which is very unlikely). The best way to initially calibrate the map is to use Google Earth or similar to zoom in on each corner of the map to find the extents. Cheers, Stephen | |
ChrisM 9:45 Location: Phone Model: | " This wouldn't really help in realigning the map in the Map Organiser, since each coordinate would have to be out by exactly the same amount for this to work (which is very unlikely). " Interesting, so is there not a simple linear relationship between the points and their coordinates? ie you can't just apply a single transformation to the whole map then (like move all points (say)0.001 degrees North and 0.002 degrees West ). I imagined that you just did something like fixing the map to a point in the 'space' that represents 'where I am now', and that you could just 'slide' that map a few seconds in any direction. Is it not that simple...? :-) Chris. | |
Stephen 9:56 Location: Phone Model: | Hi Chris, I think I'm getting a little confused!! The way the re-align function works *is* as you say, by effectively applying a single translation to the whole map (I do it at the last stage in screen coordinates/pixels, rather than world space, but it amounts to the same thing). What I meant when I said that this doesn't really help with the MapOrganiser is that it is unlikely that the four extents specified (lat min, lat max, lng min, lng max) would each have the same error. For instance if the lat min figure is too large and the lat max figure is too small, then there would be no single translation that could be applied that would completely remove the error (it would need scaling as well to achieve this in this case). Does that make any sense??!! Cheers, Stephen | |
ChrisM 10:54 Location: Phone Model: | Doh! <plunk> (This is the sound of a penny dropping) Don't worry! I'm the confused one, not you. Yes, I see what you mean. So in fact, the adjusting that is done on the phone probably won't totally solve the problem most of the time. If I've got the extents in MapOrganiser wrong then the map will not only be slightly miss-aligned, it will also be slightly the wrong scale. So even if I set the alignment using the phone's adjusting perfectly to where I was, if I travelled (for example) 10 miles along a dead straight line, I'd find that the distance travelled on the map was a bit further/shorter than it should be. And in fact if the N/S scaling error was different to the E/W one then I'd also appear to have deviated slightly from the line as shown on the map... I see now that it would be almost impossible to 'back-calibrate' the map via the re-aligning on the phone. I'll just have to take a bit more time/effort and try to be more accurate when I'm getting my coordinates from whatever mapping site I'm using. Cheers, Chris. | |
Stephen 12:02 Location: Phone Model: | Yep, thats definitely the best course of action - the more accuracy you maintain in the MapOrganiser, the better it will be on the phone. The main occasion when the re-align function will work acceptibly is if you are using a massive map image, in which you are only moving around in a tiny area of it. Over this small area the errors will be fairly consistent, but the further you move away from the original point where you first set the re-align location, the worse the errors will become... Cheers, Stephen | |
(You must be logged in to post a reply to this thread)