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Thread: Google earth's ruler

  1. #1
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    Default Google earth's ruler

    Hello all... I'm trying to build a route using google earth imaging, and was wondering if google earth's ruler is pretty accurate for measuring?

    Thanks
    Jim

  2. #2
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    Default

    Spot on I believe. I used it to make some 720 square basemaps once and they fitted well enough, but in any case the accuracy has gotta be more than good enough for Trainz...
    checkrail.com...freeware routes for Trainz

  3. #3
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    I used the Google ruler to plot my route which is a copy of the mainline in my local area.

    It worked a treat and I was able to get a very accurate fix on the track layout by drawing ruler lines from bridge to bridge in Google and then copy them on my Trainz baseboards as I stamped the track splines down at each bridge point.

    (I would orient the baseboard with North uppermost and get each angle by holding a pencil against the screen in the Google map - then switching to surveyer I could drag the Trainz ruler out along the baseboard in the same direction and angle)

    Afterwards I visited a couple of bridges along the way (in real life) and was astounded at the accuracy of the track angles and curves.

    Go for it - you won't look back

    Have fun - Nij

  4. #4
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    What these guys said. Although I got this crazy notion to test it. So I pulled a measurement between to two fixed points and then went and measured. To quote Andrew, it was spot on.

  5. #5
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    I've used it as well and it's about as accurate as you are going to get, I've also used it to get the size of buildings, very handy.
    Malc


  6. #6
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    What a great idea to use Google Earth.

    Any other tips on using it?

    - Cam

  7. #7
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    Plot your mainlines at the end of straight sections as best you can see in the GoogleEarth image, and use the track straightening tool for those sections, then the curved track joining them will be pretty much spot on. Keep an eye out for slight bends.

    --

    Something else I found works beautifully - you can also use the "Trig Station" or "Lat-Long reader" in surveyor to plot points exactly - this is helpful over great distances rather than using a Surveyor ruler, and is certainly accurate enough for Trainz applications and can be used on DEM maps provided it is set up accurately to begin with.

    The procedure I use to do this is to load up GoogleEarth and and use the "Add Placemark" button and start laying out placemarks at all the relevant spots you want to transfer into your Trainz route accurately. GE will even be so kind as to remember them from one session to the next! Name them as you go with a system that you are comfortable with.

    The most important Placemark you will put down in GE is the one on which you will base the location of the "World Origin" in Surveyor. This part can be tricky, especially if you are using a DEM terrain map, as the location must be findable on a blank DEM map. You can use mountain peaks, trace out the flat water areas on the DEM map and use an obvious point along the coast, or use the very corner of the DEM map, anywhere is good provided you know the exact global co-ordinates and can find it in Surveyor. Though it is easiest, I personally am not comfortable with using mountaintops, as I am not sure if Trainz compensates distance measuring over irregular angles. You get the picture here - this step is critical - if it is wrongly placed then everything else you find using the "trig station" object will be wrong by the same margin.

    Now that you have laid out your relevant Placemarks in GE, if you right click on the Placemark and select "Properties" it's exact global co-ordinates will be displayed for you. Take note of these co-ordinates for all of the Placemarks. This is a tedious process, but I found it worth the time. I found it easier using a spreadsheet for this bit.

    Enter your route using Surveyor, find the exact location where you must put the "World Origin", place it and simply edit it's properties to reflect that precise location (and elevation!) that you got from GE. Once this is done accurately, any "Trig Station" or "Lat-Long reader" object placed on the map will display it's precise location using global co-ordinates BASED ON THE LOCATION OF THE WORLD ORIGIN.

    I laid out a huge route this way and it worked fine. There is a major concern though, especially if maths and global co-ordinates are not your strong points. GOOGLE EARTH AND TRAINZ USE DIFFERENT FORMATS TO DISPLAY THEIR CO-ORDINATES. More specifically, GE uses the full "Degrees, Minutes, Seconds" format in which the seconds of a degree have the decimal place. In Trainz, the minutes of a degree have the decimal place. So you must convert the GE format to the Trainz format using a standard formula. Here again, using a spreadsheet comes in handy, I converted many hundreds of such co-ordinates in just a few minutes by copying-and-pasting the formula.

    For the benefit of any who are not motivated to work it out but would like to try this out, the formula for converting the GE format of degree "minutes and seconds" to the decimalised Trainz format is:

    minutes of a degree + (seconds of a degree / 60)

    Calculate this to 3 decimal places to exactly match the Trainz format.

    The full degrees figure (the first number) stays the same of course, and be sure to get the North/South and East/West part right when editing the world origin, or the result will be rather confusing. I learned that lesson the hard way.

    --

    This procedure will heat your brain up a bit, and is tedious if you have a lot of GE Placemarks to manually write down or copy into your spreadsheet, but once you have done the first couple of locations correctly you will not go back to stretching rulers out over long distances ever again.

    Hope this will help someone. If you want a DLS example of this procedure, checkout the route I uploaded to the DLS called "MagLev - Lathen Test Track, Germany" It was laid out using this procedure, even though it is small. I simply used the most northerly point of the north loop as the World Origin and plotted everything from there using the "Lat-Long reader". It was a flat route so I didn't worry about the elevation. I believe the W-O still carries it's starting co-ordinates that I got from Google Earth and converted to the Trainz format.

    The version of GoogleEarth I use is 6.1.0.5001, and Trainz 2010 SP3.

  8. #8

    Default

    Quote Originally Posted by anathoth71 View Post
    Plot your mainlines at the end of straight sections as best you can see in the GoogleEarth image, and use the track straightening tool for those sections, then the curved track joining them will be pretty much spot on. Keep an eye out for slight bends.

    --

    Something else I found works beautifully - you can also use the "Trig Station" or "Lat-Long reader" in surveyor to plot points exactly - this is helpful over great distances rather than using a Surveyor ruler, and is certainly accurate enough for Trainz applications and can be used on DEM maps provided it is set up accurately to begin with.

    The procedure I use to do this is to load up GoogleEarth and and use the "Add Placemark" button and start laying out placemarks at all the relevant spots you want to transfer into your Trainz route accurately. GE will even be so kind as to remember them from one session to the next! Name them as you go with a system that you are comfortable with.

    The most important Placemark you will put down in GE is the one on which you will base the location of the "World Origin" in Surveyor. This part can be tricky, especially if you are using a DEM terrain map, as the location must be findable on a blank DEM map. You can use mountain peaks, trace out the flat water areas on the DEM map and use an obvious point along the coast, or use the very corner of the DEM map, anywhere is good provided you know the exact global co-ordinates and can find it in Surveyor. Though it is easiest, I personally am not comfortable with using mountaintops, as I am not sure if Trainz compensates distance measuring over irregular angles. You get the picture here - this step is critical - if it is wrongly placed then everything else you find using the "trig station" object will be wrong by the same margin.

    Now that you have laid out your relevant Placemarks in GE, if you right click on the Placemark and select "Properties" it's exact global co-ordinates will be displayed for you. Take note of these co-ordinates for all of the Placemarks. This is a tedious process, but I found it worth the time. I found it easier using a spreadsheet for this bit.

    Enter your route using Surveyor, find the exact location where you must put the "World Origin", place it and simply edit it's properties to reflect that precise location (and elevation!) that you got from GE. Once this is done accurately, any "Trig Station" or "Lat-Long reader" object placed on the map will display it's precise location using global co-ordinates BASED ON THE LOCATION OF THE WORLD ORIGIN.

    I laid out a huge route this way and it worked fine. There is a major concern though, especially if maths and global co-ordinates are not your strong points. GOOGLE EARTH AND TRAINZ USE DIFFERENT FORMATS TO DISPLAY THEIR CO-ORDINATES. More specifically, GE uses the full "Degrees, Minutes, Seconds" format in which the seconds of a degree have the decimal place. In Trainz, the minutes of a degree have the decimal place. So you must convert the GE format to the Trainz format using a standard formula. Here again, using a spreadsheet comes in handy, I converted many hundreds of such co-ordinates in just a few minutes by copying-and-pasting the formula.

    For the benefit of any who are not motivated to work it out but would like to try this out, the formula for converting the GE format of degree "minutes and seconds" to the decimalised Trainz format is:

    minutes of a degree + (seconds of a degree / 60)

    Calculate this to 3 decimal places to exactly match the Trainz format.

    The full degrees figure (the first number) stays the same of course, and be sure to get the North/South and East/West part right when editing the world origin, or the result will be rather confusing. I learned that lesson the hard way.

    --

    This procedure will heat your brain up a bit, and is tedious if you have a lot of GE Placemarks to manually write down or copy into your spreadsheet, but once you have done the first couple of locations correctly you will not go back to stretching rulers out over long distances ever again.

    Hope this will help someone. If you want a DLS example of this procedure, checkout the route I uploaded to the DLS called "MagLev - Lathen Test Track, Germany" It was laid out using this procedure, even though it is small. I simply used the most northerly point of the north loop as the World Origin and plotted everything from there using the "Lat-Long reader". It was a flat route so I didn't worry about the elevation. I believe the W-O still carries it's starting co-ordinates that I got from Google Earth and converted to the Trainz format.

    The version of GoogleEarth I use is 6.1.0.5001, and Trainz 2010 SP3.
    And if insted using the bookmarks, make a path along the route and export to trainz? is that possible

  9. #9
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    I do not know if that is possible. I assume some kind of plug-in program for Google Earth would be required. The method I described requires no special programming except a simple spreadsheet, or even a pocket calculator. Just patience and a desire for accuracy.

    I have never used the Add Path function of Google Earth. Let me know if you work out a way to do that.

  10. #10
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    Quote Originally Posted by anathoth71 View Post
    I do not know if that is possible. I assume some kind of plug-in program for Google Earth would be required. The method I described requires no special programming except a simple spreadsheet, or even a pocket calculator. Just patience and a desire for accuracy.

    I have never used the Add Path function of Google Earth. Let me know if you work out a way to do that.
    There are on-line calculators that do the conversion to decimal minutes however for those without a suitable spreadsheet, I just used a calculator.

    I would imagine the add path could be created as a Google Earth overlay and used in the same way as using a GE image as a basemap?

    Below may be useful to anyone reading this thread?

    There was but due to the PC problems I lost it and can't find it again on the web yet, a GE Addon that you could add a custom size grid as an overlay which is handy for a Trainz baseboard sized grid. think it was from a non english site, still looking for it when I have a few spare minutes

    Microdem current version as of this year can export a dem as an overlay to GE

    There is the SRTM.4.1 kml that you can select the DEM data directly from a GE KML overlay, just Google SRTM 4.1 kml.

    For UK users there is now some excellent free mapping and DEM stuff available from http://www.ordnancesurvey.co.uk/oswe...-opendata.html, the terrain produced just running a couple of tests through microdem is far better and more accurate than anything I have found for UK from anywhere else yet, I would imagine even better using Transdem and the 5m grid. Haven't worked out what to do with a lot of the stuff from there yet though I'm sure it can be useful in Trainz.
    Malc


  11. #11

    Default

    Quote Originally Posted by anathoth71 View Post
    you can also use the "Trig Station" or "Lat-Long reader" in surveyor to plot points exactly ... certainly accurate enough for Trainz applications ... and can be used on DEM maps
    ...
    The most important Placemark ... location of the "World Origin" in Surveyor. This part can be tricky, especially if you are using a DEM terrain map, as the location must be findable on a blank DEM map.
    This approach would only be "accurate" if the map projection of the "DEM map" is the same as the one used internally by Trainz to process latitude/longitude.

    "Map projection" is the mathematical algorithm to transform the curved surface of Mother Earth to a planar and usually metric Cartesian coordinate system like the one used in Trainz which is called Trainz World Coordinates.

    The typical map projection when working with MicroDEM and HOG was or is UTM (Universal Transverse Mercator). Unfortunately, UTM is not the projection used by Trainz. We don't know which one they actually employ, but as long as it is different to the one for the MicroDEM/HOG-based or any other DEM map you will encounter systematic error, increasing in a non-linear fashion with growing distance to the Trainz World Origin.

    Since you don't start with accurate mapping anyway - the somewhat arbitrary placement of the World Origin in the first place - you may not notice the error at all. Limited resolution of the DEM, e.g. SRTM, may also help concealing the error. But be assured, it is there, and it will matter for a longer route.

  12. #12
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    Geophil - agreed. I did notice some cumulative error creeping in at greater distances from the world origin, and forgot to mention it in my original post, thanks for the reminder. The plotting of the route I refer to took place quite a while ago.

    I should have included a paragraph advising the moving of the World Origin every 100km or less. This is not a difficult complication, as a conveniently located bridge end or something can be used for the new World Origin datum, and adjusted for the error. Again, I found that this system was sufficiently accurate for Trainz purposes and resulted in a very accurate track alignment with localised alteration of items like bridge ends or tunnel entrances requiring fairly minimal adjustment. The amount of that adjustment depends on lots of other variables, one of them being the distance from the World Origin.

  13. #13

    Default

    What you could do in your approach is to abandon geographic coordinates (lat/long) altogether and use Cartesian coordinates throughout. Provided that your DEM map, presumably created by MicroDEM/HOG, is based on UTM, you could switch to UTM in Google Earth and activate Trainz World Coordinates display (TWC) in Trainz Surveyor. Both coordinates systems are metric, so the transformation is reduced to a simple "translation" (in transformation math terminiology):

    twc - twc0 = utm - utm0

    or

    twc = utm - (utm0 - twc0)

    You still need to define your initial anchor point utm0 → twc0, but you won't have systematic error any longer, moving away from your anchor point.

    The manual utm0 to twc0 mapping approximation is still required, since the MicroDEM/HOG approach loses georeferencing information during the process.

  14. #14
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    Straight cartesian could be an option for a project from the ground up, but some route makers might tolerate the very small errors that creep in over large distances using the Trainz coordinate system, given that that error only amounts to a few meters over a distance of many many kilometres, and I for one tend to make small local adjustments to make track features fit the terrain model better anyway. Less technical users using DEM terrain they themselves didn't create might find it easier as well. Either way it is still way better than laying out long rulers. The cumulative errors of using the ruler method seemed much greater when I used to use it.

    As you say, the starting point still has to be determined accurately. It is good that there are a number of ways to tackle the horizontal accuracy issue these days, years ago even DEM terrain was just a remote fantasy. It's all good.

  15. #15

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    I tested the discrepancy of the Trainz internal map projection and UTM some time ago, since this question had come up several times in the past already.

    Here is what I wrote four years ago:
    http://forums.auran.com/trainz/showt...899#post219899

    In that test it turned out that the difference between between the Trainz projection and UTM reached 20 m within 1 km from the World Origin, increasing to 600m for a point 38 km away from the origin.

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