Trying to create DEM data from Google Earth with correct projection/coordinates

Hi All, 

I am new to GlobalMapper and a novice in this whole field so please forgive my ignorance.  I am using software that can take LiDAR data, overlay it onto an OpenStreetMaps (with features of a golf course mapped out onto it) and then create a highly accurate simulation of a golf course.  

There are a lot of sources for downloading LiDAR data across the US or other countries, however, there are also a lot of places where data is not available.  In Japan where I am, for example, I can download 5M DEM data for most of the country (although there are a lot of spots where the land has not been mapped out).  Using GlobalMapper with the LiDAR module, I have been able to take this data, classify all of the points to ground (the data is all unclassified), and then export to LAS file and have been able to successfully import that with my tool to come up with a fairly good representation of the golf course.  

Now, there are some courses that I would like to create where there is no readily available LiDAR or DEM data.  So my idea is to create a DEM from Google Earth by laying down points on a path all around the golf course.  I save that as a kmz file and then going to gpsvisualizer.com to get elevation data for this.  I save this as a txt file and I end up with a text file with latitude, longitude, and altitude data. 

I have been able to import this file into GM and classify the data and export to LAS, however, when I try to import this LAS file into the tool to add to the golf simulator, the golf course doesn't show up where it is supposed to be.  I am not quite sure what I am doing wrong here.  

I do notice that when I try to export this data as a LAS file, if I draw a box around the selected area, it is showing geographical coordinates that are completely different from the actual location.  Below is a link to a dropbox folder with a couple of files that I am working on.  This is a map of the golf Course at Marina Bay located in Singapore.  I believe that I may be using the wrong projection system for importing but I am really not sure what I should be using. 

https://www.dropbox.com/sh/7jpgmlq3mi4g4dv/AACheMZ9RXI4yb7_Gc76en2da?dl=0

If anyone has any idea on how to get accurate data from this it would be greatly appreciated.  

Answers

  • sphillipssphillips Posts: 206
    My understanding is that Google Earth terrain is around 90m resolution (each pixel is 90m across). I have imported your TXT data and I can see 90m tiles. I couldn't get the LAS file to load in the right place but when I removed the header and first column from the TXT file with Excel it loaded fine. The quality is that good though.

    There are various sources that cover most of the world. If you click on the globe icon in GM you can find SRTM (which is ~30m resolution) under **POPULAR SOURCES** > SRTM Worldwide Elevation Data (1-arc second..). Also there is the ASTER GDEM v2 in that list too.

    Other sources can be found online here but note some country have their own DEM/LiDAR sources that are much better: 

    https://portal.opentopography.org/raster?opentopoID=OTALOS.112016.4326.2
    https://www.eorc.jaxa.jp/ALOS/en/aw3d30/data/index.htm


    sirish19
  • sphillips said:
    My understanding is that Google Earth terrain is around 90m resolution (each pixel is 90m across). I have imported your TXT data and I can see 90m tiles. I couldn't get the LAS file to load in the right place but when I removed the header and first column from the TXT file with Excel it loaded fine. The quality is that good though.

    There are various sources that cover most of the world. If you click on the globe icon in GM you can find SRTM (which is ~30m resolution) under **POPULAR SOURCES** > SRTM Worldwide Elevation Data (1-arc second..). Also there is the ASTER GDEM v2 in that list too.

    Other sources can be found online here but note some country have their own DEM/LiDAR sources that are much better: 

    https://portal.opentopography.org/raster?opentopoID=OTALOS.112016.4326.2
    https://www.eorc.jaxa.jp/ALOS/en/aw3d30/data/index.htm


    Hi sphillips, thank you very much for your reply. From a very basic Google search, I had thought that Google Earth resolution ranged between 15 M and 15 cm but that did seem a bit optimistic.  Where did you find the 90 M resolution? Does that mean that you see only one single elevation value for each 90 M tile?  When I look at the elevation ranges for some area, even a small area smaller than 90 M, I do see the differing elevation numbers so I had assumed that it probably had a little better resolution than that.  I believed that the resolution of Google Earth really depended on the location and the thoroughness of the mapping, but I honestly have no idea. 

    When you say that you see 90 M tiles when importing my TXT data, can you explain how to see that in GM?  

    I had a look at the SRTM and ASTER GDEM v2 in the popular sources and I do see the map to come up. This seems to be a very broad map, however, so I am not quite sure how to pinpoint a very specific location such as a golf course from that.  Also, what I would like to do is to be able to create a point cloud from this map, classify the points as ground, and then export into a LAS file.  Could you help me to understand the proper way to do that in GM?

    Rgarding the  other online sources that you listed, I could open opentopography but I couldn't open the eorc data as it seems this needs a registration.

    Sorry for all of the newbie questions but I really appreciate any support and advice that I can get. 
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