HGT - Less Than Perfect
#1
Posted 29 April 2018 - 09:04 AM
1. Hills, where there are none in real life. I finally figured out that HGTs can include the height of highways, not just the ground.
2. HGTs don't necessarily align with other maps, they can be off by around 30-40 meters.
This picture illustrates both problems.
http://www.johnkorchok.com/images/HGTerrors.png
You can see what appears to be a hill in the green-gold area, leading down to the track on the right. In real life, the ground is very flat former swampland. The "hill" the the Highway 80 overpass that runs over where the tracks will be. So after applying the HGT, I'll have to excavate to restore the original terrain height in 1876.
You can also see Highway 80 as shown on the map and the same rise on the HGT. They don't match, with the HGT showing the overpass rise as being about 30 meters too far south.
HGTs are very convenient, but if you're trying to be precise, a good topo map is still a necessary cross-reference.
#2
Posted 29 April 2018 - 09:15 AM
#3
Posted 29 April 2018 - 09:41 AM
#5
Posted 29 April 2018 - 11:47 AM
#6
Posted 30 April 2018 - 08:00 PM
Terrain Grid
http://www.johnkorchok.com/images/terrain.png
#7
Posted 03 May 2018 - 02:49 PM
Under Search Criteria tab, it's simplest zoom in and click on the map for the area you want to download.
On the Data Sets tab, expand NASA LPDAAC Collections, then NASA SRTM (SRTM 3) Collections and check NASA SRTM3 SRTMGL1. The 1 stands for 1 arc-second.
Then click on the Results tab. Each map will have a small download icon. Choose Standard Format which will have a 7 - 10 MB file size.
#8
Posted 03 May 2018 - 04:48 PM
1 arc second resolution is like, oh 20-30 years old. IMO worthless for anything that isn't almost flat.
#9
Posted 13 May 2018 - 08:05 AM
Genma Saotome, on 03 May 2018 - 04:48 PM, said:
Thanks for the tip. I'm aware that other formats have higher resolution, but I was writing about the available HGTs. 1 arc-second is approximately 30 meters and the current data is 18 years old.
#10
Posted 28 June 2018 - 03:57 PM
There is 1m resolution Lidar data availible but only over a VERY VERY ;limited area.
Lindsay
#11
Posted 28 June 2018 - 04:52 PM
jkorchok, on 13 May 2018 - 08:05 AM, said:
Format and resolution are different things. .hgt could probably hold 1/9 sec arc data and you can probably find 1/9th arc data in other formats too.
The gotcha is usually a given source only publishes data in one format and if they're where you go you get that format... and whatever resolution they can give you.
Goku's program needs to handle different file formats and whatever resolution the data comes in. People are not going to want to use 90m data just because it is .hgt when 10m data in geotiff is available for the same location. They're going to want to use hte best they can get their hands on w/o regard to file type.
#12
Posted 10 January 2019 - 05:02 AM
Can ORTS take whatever resolution we throw at it - or is it limited on how detailed it can go ?
Thanks...
Regards,
Scott
#13
Posted 10 January 2019 - 10:30 AM
#14
Posted 10 January 2019 - 10:56 AM