Scenery:Terrain Model - Revision history

129.240.228.21 at 13:08, 6 March 2007

2007-03-06T13:08:08Z

← Older revision		Revision as of 13:08, 6 March 2007
Line 24:		Line 24:
	if S is tile size and <math>\phi</math> is the latitude of the tile, we get:		if S is tile size and <math>\phi</math> is the latitude of the tile, we get:

			<blockquote>
	<math>		<math>
	S_N = S		S_N = S
Line 30:		Line 31:
	S_E = \frac{S}{\cos(\phi)}		S_E = \frac{S}{\cos(\phi)}
	</math>		</math>
			</blockquote>

	Usually we will select a reference latitude <math>\phi_R</math> which is used for		Usually we will select a reference latitude <math>\phi_R</math> which is used for

129.240.228.21 at 13:06, 6 March 2007

2007-03-06T13:06:32Z

← Older revision		Revision as of 13:06, 6 March 2007
Line 3:		Line 3:

	The earth model used for the 3D visualisation in GeoGFX is a sphere		The earth model used for the 3D visualisation in GeoGFX is a sphere
	with radius $R = 6378000$ m. For visualization purposes, the		with radius R = 6378000 m. For visualization purposes, the
	elliptical shape of the earth can safely be ignored. However, all		elliptical shape of the earth can safely be ignored. However, all
	geographic processing and reprojection of input data is done in the		geographic processing and reprojection of input data is done in the
	WGS84 datum so all input data will be matched to the same earth model.		WGS84 datum so all input data will be matched to the same earth model.

	A GeoGFX terrain model is divided into ~~\emph{~~blocks}, each block is a		A GeoGFX terrain model is divided into <i>blocks</i>, each block is a
	rectangular section of the earth surface measured in degrees of		rectangular section of the earth surface measured in degrees of
	latitude and longitude. Each block is further divided into a regular		latitude and longitude. Each block is further divided into a regular
	grid of ~~\emph{~~tiles}. The number of tiles in a block should normally		grid of <i>tiles</i>. The number of tiles in a block should normally
	be a power of two, and it should also be the same in north- and		be a power of two, and it should also be the same in north- and
	east-direction, i.e a block can be 8~~$\times$~~8, 16~~$\times$~~16 etc.		east-direction, i.e a block can be 8 x 8, 16 x 16 etc.
	Neighboring blocks must have the same number of tiles.		Neighboring blocks must have the same number of tiles.

Line 22:		Line 22:
	north or south. To keep our tiles more equal sided, we compensate for		north or south. To keep our tiles more equal sided, we compensate for
	this by dividing the east tile size by the cosine of the latitude, i.e		this by dividing the east tile size by the cosine of the latitude, i.e
	if $S$ is tile size and $\phi$ is the latitude of the tile, we get:		if S is tile size and <math>\phi</math> is the latitude of the tile, we get:

	~~\begin{eqnarray}~~		<math>
	S_N &= S\\		S_N = S
	S_E &= \frac{S}{\cos(\phi)}		</math><br>
	~~\end{eqnarray}~~		<math>
			S_E = \frac{S}{\cos(\phi)}
			</math>

	Usually we will select a reference latitude $\phi_R$ which is used for		Usually we will select a reference latitude <math>\phi_R</math> which is used for
	all terrain blocks that should be connected. For example for a		all terrain blocks that should be connected. For example for a
	european terrain model covering Germany and the Alps we could select		european terrain model covering Germany and the Alps we could select
	50~~\degrees~~~north as reference latitude for all the terrain blocks. For		50° north as reference latitude for all the terrain blocks. For
	a scandinavian terrain model we would select for example 62~~\degrees~~.		a scandinavian terrain model we would select for example 62°.
	At this reference latitude a tile would be equal size in north and		At this reference latitude a tile would be equal size in north and
	east direction.		east direction.

Ola: Reverted edits by Ola (Talk); changed back to last version by 129.240.228.21

2007-03-06T12:59:59Z

Reverted edits by Ola (Talk); changed back to last version by 129.240.228.21

← Older revision		Revision as of 12:59, 6 March 2007
Line 24:		Line 24:
	if $S$ is tile size and $\phi$ is the latitude of the tile, we get:		if $S$ is tile size and $\phi$ is the latitude of the tile, we get:

	~~<math>~~		\begin{eqnarray}
	\S_N &= S\\		S_N &= S\\
	~~</math>~~		S_E &= \frac{S}{\cos(\phi)}
	~~<math>~~		\end{eqnarray}
	\S_E &= \frac{S}{\cos(\phi)}
	~~</math>~~

	Usually we will select a reference latitude $\phi_R$ which is used for		Usually we will select a reference latitude $\phi_R$ which is used for

Ola at 12:47, 6 March 2007

2007-03-06T12:47:29Z

← Older revision		Revision as of 12:47, 6 March 2007
Line 26:		Line 26:
	<math>		<math>
	\S_N &= S\\		\S_N &= S\\
			</math>
			<math>
	\S_E &= \frac{S}{\cos(\phi)}		\S_E &= \frac{S}{\cos(\phi)}
	</math>		</math>

Ola at 12:47, 6 March 2007

2007-03-06T12:47:13Z

← Older revision		Revision as of 12:47, 6 March 2007
Line 25:		Line 25:

	<math>		<math>
	S_N &= S\\		\S_N &= S\\
	S_E &= \frac{S}{\cos(\phi)}		\S_E &= \frac{S}{\cos(\phi)}
	</math>		</math>

Ola at 12:46, 6 March 2007

2007-03-06T12:46:46Z

← Older revision		Revision as of 12:46, 6 March 2007
Line 25:		Line 25:

	<math>		<math>
	~~\begin{eqnarray}~~
	S_N &= S\\		S_N &= S\\
	S_E &= \frac{S}{\cos(\phi)}		S_E &= \frac{S}{\cos(\phi)}
	~~\end{eqnarray}~~
	</math>		</math>

Ola at 12:46, 6 March 2007

2007-03-06T12:46:15Z

← Older revision		Revision as of 12:46, 6 March 2007
Line 24:		Line 24:
	if $S$ is tile size and $\phi$ is the latitude of the tile, we get:		if $S$ is tile size and $\phi$ is the latitude of the tile, we get:

			<math>
	\begin{eqnarray}		\begin{eqnarray}
	S_N &= S\\		S_N &= S\\
	S_E &= \frac{S}{\cos(\phi)}		S_E &= \frac{S}{\cos(\phi)}
	\end{eqnarray}		\end{eqnarray}
			</math>

	Usually we will select a reference latitude $\phi_R$ which is used for		Usually we will select a reference latitude $\phi_R$ which is used for

Ola at 12:45, 6 March 2007

2007-03-06T12:45:53Z

← Older revision		Revision as of 12:45, 6 March 2007
Line 40:		Line 40:
	latitude of the terrain block is used. (This block would then only be		latitude of the terrain block is used. (This block would then only be
	able to connect with other blocks on the same latitude).		able to connect with other blocks on the same latitude).


	~~Ola tester testen:~~
	~~<math>\sqrt{1-e^2}</math>~~


	[[Category:Scenery]]		[[Category:Scenery]]

Ola at 12:38, 6 March 2007

2007-03-06T12:38:57Z

← Older revision		Revision as of 12:38, 6 March 2007
Line 40:		Line 40:
	latitude of the terrain block is used. (This block would then only be		latitude of the terrain block is used. (This block would then only be
	able to connect with other blocks on the same latitude).		able to connect with other blocks on the same latitude).


			Ola tester testen:
			<math>\sqrt{1-e^2}</math>


	[[Category:Scenery]]		[[Category:Scenery]]

Ola at 12:34, 6 March 2007

2007-03-06T12:34:51Z

← Older revision		Revision as of 12:34, 6 March 2007
Line 40:		Line 40:
	latitude of the terrain block is used. (This block would then only be		latitude of the terrain block is used. (This block would then only be
	able to connect with other blocks on the same latitude).		able to connect with other blocks on the same latitude).


	~~Ola tester testen:~~
	~~<math>\sqrt{1-e^2}</math>~~


	[[Category:Scenery]]		[[Category:Scenery]]