devin

10-25-2007, 11:16 AM

Hi,

I've been reading through some prior threads in order to properly import a digital elevation map into LW. I think I've got that part correct now (I hope). I need to ensure that it's the proper scale, however, and thought I'd post. I pulled a 7.5 minute tile/area. How do I actually determine the proper distance that this covers. I've seen a number of figures such as 1cm=240m, 1 min.=1.15 miles, etc. The problem is that these different methods give me different results. Is there a clear cut method for this that's accurate? Should the model pulled from the DEM data already be accurate? If the elevation is actually correct, the distance along the remaining axes should be true as well, right?

To add to the confusion, one tutorial had me pull the map at NED 1/3" and then convert it using 3DEM to a UTM Projection. This causes the originally square tile to become more rectangular (taller than wide). Is the converted projection map the true proportion? This is all a little Greek to me.

Thanks in advance for any insight.

Devin (the confused)

I've been reading through some prior threads in order to properly import a digital elevation map into LW. I think I've got that part correct now (I hope). I need to ensure that it's the proper scale, however, and thought I'd post. I pulled a 7.5 minute tile/area. How do I actually determine the proper distance that this covers. I've seen a number of figures such as 1cm=240m, 1 min.=1.15 miles, etc. The problem is that these different methods give me different results. Is there a clear cut method for this that's accurate? Should the model pulled from the DEM data already be accurate? If the elevation is actually correct, the distance along the remaining axes should be true as well, right?

To add to the confusion, one tutorial had me pull the map at NED 1/3" and then convert it using 3DEM to a UTM Projection. This causes the originally square tile to become more rectangular (taller than wide). Is the converted projection map the true proportion? This is all a little Greek to me.

Thanks in advance for any insight.

Devin (the confused)