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<DIV><FONT face=Arial size=2>hello,</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV>>>>>>And is this height stored relative to some value ( like
any value seen<BR>in ModelTiepointTag .. )</DIV>
<DIV> </DIV>
<DIV><FONT face=Arial size=2>If you don't only need to display the data, which
is not really the aim of DEM data, you do need to take into account that data
are "elevations" (which you call heights). Maybe you have to make calculations
from your DEM : terrain analysis, line of sight, hypsometric representations, 3D
display, ....</FONT></DIV>
<DIV><FONT face=Arial size=2>Elevations are relative to a vertical reference,
usually mean sea level. Your geokeys unfortunately don't show any information on
it.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>If your application is not very demanding
(accuracy, safety, ...) you can just don't mind or assume that the vertical
reference is EGM96 (guessed from WGS84 used for geographic reference
system).</FONT></DIV>
<DIV><FONT face=Arial size=2>Anyway if your application is critical, you have to
check it from the producer of the data.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>You also have to check how the elevation is
</FONT><FONT face=Arial size=2>encoded in the 16 bits sample. Are elevations
meters of feet ? How are encoded the negative values (keep in mind that some
regions of the world are below the sea level). Is there any "no data"
convention?</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Mind too that DEM are usually "PixelIsPoint". What
is your GTRasterTypeGeoKey ?</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Hope that helps</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Pascal</FONT></DIV>
<DIV><FONT face=Arial size=2>France</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><BR></DIV>
<BLOCKQUOTE
style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B>
<A title=roorkee123@gmail.com href="mailto:roorkee123@gmail.com">Prajjval</A>
</DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A title=geotiff@lists.maptools.org
href="mailto:geotiff@lists.maptools.org">geotiff@lists.maptools.org</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Wednesday, September 06, 2006 9:26
PM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> [Geotiff] Re: Geotiff Digest,
Vol 26, Issue 1</DIV>
<DIV><BR></DIV>Hello,<SPAN style="COLOR: rgb(255,0,0)"></SPAN><BR><BR>I think
that there is no such difference in reading the geotiff, either it is a DEM or
anything else.<BR>So read the geotiff image data and use it as is. Means it
does not matter that the data is DEM or pixel value. The DEM data which is in
geotiff format means that the values stored in it are height. <BR><BR>Also the
value stored in geotiff is always used as it is and it is not relative to
anyother value.<BR><BR>The ModelTiepointTag stores the top left location of
your geotiff image. And ModelPixelScaleTag stores the pixel size of your
geotiff image. <BR><BR>Vineet Bhargava<BR>India<BR><BR>Firstly I
am new to the geotiff world . <BR><BR><BR>I am trying
to read DEM data which is supplied in geotiff format.
Its<BR>geotiff image with 181 rows x 181 cols<BR>I wrote some code
to read the basic tags. And they are as follows
<BR><BR>SAMPLESPERPIXEL 1<BR>TIFFTAG_BITSPERSAMPLE 16<BR>TIFFTAG_PHOTOMETRIC 1
(1 /* min value is black */
)<BR>TIFFTAG_PLANARCONFIG 1 ( single plane
image)<BR><BR>Now my doubt how do I read the height data stored in this
Geotiff Image <BR>?<BR>And is this height stored relative to some value ( like
any value seen<BR>in ModelTiepointTag .. )<BR><BR>Any
API's in libgeotiff / pointers on handling Digital Elevation
data<BR>in geotiff will be appreciated . <BR><BR><BR><BR>FYI ..<BR>This is the
Geotiff info for the input data<BR><BR>Geotiff_Information:<BR>
Version: 1<BR> Key_Revision: 1.0<BR>
Tagged_Information:<BR> ModelTiepointTag
(2,3):<BR>
0 0 0
<BR>
6.99861111
54.0013889
0<BR> ModelPixelScaleTag
(1,3):<BR>
0.00277778
0.00277778
0<BR> End_Of_Tags.<BR>
Keyed_Information:<BR> GTModelTypeGeoKey
(Short,1): ModelTypeGeographic
<BR> GTRasterTypeGeoKey (Short,1):
RasterPixelIsArea<BR> GeographicTypeGeoKey
(Short,1):
GCS_WGS_84<BR> GeogCitationGeoKey
(Ascii,6):
"wgs84"<BR> GeogAngularUnitsGeoKey
(Short,1): Angular_Degree
<BR> End_Of_Keys.<BR>
End_Of_Geotiff.<BR><BR><BR>Thanks in advance,<BR>--Chandrakant<BR>
<DIV>
<BLOCKQUOTE class=gmail_quote
style="PADDING-LEFT: 1ex; MARGIN: 0pt 0pt 0pt 0.8ex; BORDER-LEFT: rgb(204,204,204) 1px solid"><BR><BR>Today's
Topics:<BR><BR> 1. Processing Elevation data in
Geotiff<BR> (Chandrakant Mohire
(RBIN/ECM2))<BR><BR><BR>----------------------------------------------------------------------
<BR><BR>Message: 1<BR>Date: Wed, 6 Sep 2006 14:58:07 +0530<BR>From:
"Chandrakant Mohire (RBIN/ECM2)" <<A
href="mailto:Chandrakant.M@in.bosch.com">Chandrakant.M@in.bosch.com</A>><BR>Subject:
[Geotiff] Processing Elevation data in Geotiff <BR>To: <<A
href="mailto:geotiff@lists.maptools.org">geotiff@lists.maptools.org</A>><BR>Message-ID:<BR> <<A
href="mailto:6222DD7606D1314C85F63D9CF40207E00304C87C@kormail02.in.bosch.com">6222DD7606D1314C85F63D9CF40207E00304C87C@kormail02.in.bosch.com
</A>><BR>Content-Type: text/plain; charset="us-ascii"<BR><BR>Hello
,<BR><BR>Firstly I am new to the geotiff world .<BR><BR><BR>I am
trying to read DEM data which is supplied in geotiff format.
Its<BR>geotiff image with 181 rows x 181 cols <BR>I wrote some
code to read the basic tags. And they are as
follows<BR><BR>SAMPLESPERPIXEL 1<BR>TIFFTAG_BITSPERSAMPLE 16<BR>TIFFTAG_PHOTOMETRIC 1
(1 /* min value is black */
)<BR>TIFFTAG_PLANARCONFIG 1 ( single plane image)
<BR><BR>Now my doubt how do I read the height data stored in this Geotiff
Image<BR>?<BR>And is this height stored relative to some value ( like any
value seen<BR>in ModelTiepointTag .. )<BR><BR>Any
API's in libgeotiff / pointers on handling Digital Elevation data
<BR>in geotiff will be appreciated .<BR><BR><BR><BR>FYI ..<BR>This is the
Geotiff info for the input data<BR><BR>Geotiff_Information:<BR>
Version: 1<BR> Key_Revision: 1.0<BR>
Tagged_Information:<BR> ModelTiepointTag
(2,3): <BR>
0 0 0<BR>
6.99861111
54.0013889
0<BR> ModelPixelScaleTag
(1,3):<BR>
0.00277778
0.00277778
0<BR> End_Of_Tags.<BR>
Keyed_Information: <BR> GTModelTypeGeoKey
(Short,1):
ModelTypeGeographic<BR> GTRasterTypeGeoKey
(Short,1):
RasterPixelIsArea<BR> GeographicTypeGeoKey
(Short,1):
GCS_WGS_84<BR> GeogCitationGeoKey
(Ascii,6): "wgs84"
<BR> GeogAngularUnitsGeoKey (Short,1):
Angular_Degree<BR> End_Of_Keys.<BR>
End_Of_Geotiff.<BR><BR><BR>Thanks in
advance,<BR>--Chandrakant<BR><BR><BR><BR><BR><BR></BLOCKQUOTE></DIV></BLOCKQUOTE></BODY></HTML>