Terrain Database Query

[Vineet Jain]

Hi Friends,

I am using govt. surveyed topo maps for terrain data in path profile generation for microwave links & found this method accurate.

Now I tried to use the Terrain databases files which I received with Pathloss software to generate the Path profile , configuring following terrain database setting for Indian terrain

Primary database: Gtopo30 Global 30 sec

Secondary database: USGS 7.5 Minute

Datum : Ellipsoid , WGS 84

I found that the profile generated physically & via software doesn,t match and there is a variation in the elevation of the place from 5 to 80 mtrs. Generally software generated elevation is on the lower side. My observation is that over a hop/ link the the path profile pattern is 85 % matching with data taken from topo maps.

1.) Do anybody notice such variations?

2.) How accurate is the data given by terrain database software? i.e. Elevation of a particular location.

Awaiting a reply & Thanks in Advance

vineet jain

[Vic Rhys-Williams]

Not very accurate is the answer. GTopo30 Global 30sec is only accurate to 30 Arc seconds, ie. half a degree. Its better than nothing and gives an idea of the profile but if you are using 1-50k topographical mapping and plotted accurately, thats just about as good as it gets.
Cheers,

Vic R-W

[Vic Rhys-Williams]

The resolution mentioned in my previous email is in error, 30 arc seconds being half a minute and not half a degree. As mentioned this resolution is not very accurate as I myself have seen differences in altitude of 80m between the Pathloss CD and that provided by Planet 50m resolution. Hope this helps. Sorry about the typo.

Cheers,

Vic R-W

[Vineet Jain]

Thanks williams for the valuable suggestion.

Regards,

vineet jain