I opened a WORLD table (with a geographical lat/long ‘projection’) in MapInfo, and then added a line object from the latitude of +60N to the latitude of -60S; what I intended to do is to generate a uniform buffer zone of 2500km (spherical distance!) surrounding this line object.
The Buffer function with a “spherical distance” option is used , but MapInfo produces a rectangle-like zone (with 4 rounded corners). I though the buffered zone to be generated would have this feature - widths of the buffer zone in higher latitudes are much larger than those close to the Equator, due to the obvious earth shape. I could not figure out why MapInfo produces this rectangle-like buffer zone, and it seems the buffered zone generated is not being automatically projected to the projection of the underlying table.
In fact, if you change the projection of the underlying table to other world projections, the buffer zone always looks like a rectangle, surrounding the line object added in the beginning. All is not what I expected.
I wish to seek your help for clarification.
Could you please suggest how I can realize what I wanted in MapInfo? If you have resources or websites on buffering algorithms (either for vector-based objects or in a grid/raster environment), could you please suggest?
Thank you very much
kevin
---------------------------------
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RE: MI-L "problem" with spherical distance bufferi
Unfortunately MapInfo Pro's spherical buffers have never worked =
correctly
for larger areas. The problem is that the calculation is not truly =
spherical
in that the buffer distance is transformed into lat/lon units at a =
single
point. The problem here is that a degree of longitude changes size with
varying latitude, so large buffers have an increasing degree of error.
Buffers around a point always come out as ellipse-shaped and do not seem =
to
"spread out" as they approach the poles (using the standard world
projection). The only solution I know, and use, is to develop your own
buffering code for points and then apply this to all nodes in your =
source
objects.
I hope MapInfo support note this message because it's a bug in Pro that =
is
long overdue and cripples the application for use in "long distance" =
uses as
aero, shipping, space systems, etc.
Regards,
Warren Vick
Europa Technologies Ltd.
http://www.europa-tech.com
-----Original Message-----
From: Jennifer Tao [mailto:ttj_tao@yahoo.com.au]=20
Sent: 12 May 2005 13:34
To: mapinfo-l@lists.directionsmag.com
Subject: MI-L "problem" with spherical distance buffering=20
Hi,
=20
I opened a WORLD table (with a geographical lat/long 'projection') in
MapInfo, and then added a line object from the latitude of +60N to the
latitude of -60S; what I intended to do is to generate a uniform buffer =
zone
of 2500km (spherical distance!) surrounding this line object.=20
=20
The Buffer function with a "spherical distance" option is used , but =
MapInfo
produces a rectangle-like zone (with 4 rounded corners). I though the
buffered zone to be generated would have this feature - widths of the =
buffer
zone in higher latitudes are much larger than those close to the =
Equator,
due to the obvious earth shape. I could not figure out why MapInfo =
produces
this rectangle-like buffer zone, and it seems the buffered zone =
generated is
not being automatically projected to the projection of the underlying =
table.
=20
In fact, if you change the projection of the underlying table to other =
world
projections, the buffer zone always looks like a rectangle, surrounding =
the
line object added in the beginning. All is not what I expected.
=20
I wish to seek your help for clarification.=20
=20
Could you please suggest how I can realize what I wanted in MapInfo? If =
you
have resources or websites on buffering algorithms (either for =
vector-based
objects or in a grid/raster environment), could you please suggest?
=20
Thank you very much
=20
kevin
---------------------------------
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To unsubscribe, e-mail: mapinfo-l-unsubscribe@lists.directionsmag.com
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Message number: 16455
RE: MI-L "problem" with spherical distance bufferi
Unfortunately MapInfo Pro's spherical buffers have never worked correctly
for larger areas. The problem is that the calculation is not truly spherical
in that the buffer distance is transformed into lat/lon units at a single
point. The problem here is that a degree of longitude changes size with
varying latitude, so large buffers have an increasing degree of error.
Buffers around a point always come out as ellipse-shaped and do not seem to
"spread out" as they approach the poles (using the standard world
projection). The only solution I know, and use, is to develop your own
buffering code for points and then apply this to all nodes in your source
objects.
I hope MapInfo support note this message because it's a bug in Pro that is
long overdue and cripples the application for use in "long distance" uses as
aero, shipping, space systems, etc.
Regards,
Warren Vick
Europa Technologies Ltd.
http://www.europa-tech.com
-----Original Message-----
From: Jennifer Tao [mailto:ttj_tao@yahoo.com.au]
Sent: 12 May 2005 13:34
To: mapinfo-l@lists.directionsmag.com
Subject: MI-L "problem" with spherical distance buffering
Hi,
I opened a WORLD table (with a geographical lat/long 'projection') in
MapInfo, and then added a line object from the latitude of +60N to the
latitude of -60S; what I intended to do is to generate a uniform buffer zone
of 2500km (spherical distance!) surrounding this line object.
The Buffer function with a "spherical distance" option is used , but MapInfo
produces a rectangle-like zone (with 4 rounded corners). I though the
buffered zone to be generated would have this feature - widths of the buffer
zone in higher latitudes are much larger than those close to the Equator,
due to the obvious earth shape. I could not figure out why MapInfo produces
this rectangle-like buffer zone, and it seems the buffered zone generated is
not being automatically projected to the projection of the underlying table.
In fact, if you change the projection of the underlying table to other world
projections, the buffer zone always looks like a rectangle, surrounding the
line object added in the beginning. All is not what I expected.
I wish to seek your help for clarification.
Could you please suggest how I can realize what I wanted in MapInfo? If you
have resources or websites on buffering algorithms (either for vector-based
objects or in a grid/raster environment), could you please suggest?
Thank you very much
kevin
---------------------------------
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To unsubscribe, e-mail: mapinfo-l-unsubscribe@lists.directionsmag.com
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Message number: 16455
---------------------------------
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