projections and coordinate systems
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Projections and Coordinate Systems. Projections Coordinate systems Datums. Projections. The earth is a spheroid The best model of the earth is a globe. not easy to carry not good for making planimetric measurement (distance, area, angle). Maps are flat easy to carry - PowerPoint PPT PresentationTRANSCRIPT
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Projections and Coordinate Systems
1. Projections2. Coordinate systems3. Datums
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Projections
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The earth is a spheroidThe best model of the earth is a globe
•not easy to carry•not good for making planimetric measurement(distance, area, angle)
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Maps are flateasy to carrygood for measurementscaleable
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A map projection is a method for mapping spatial patterns on a curved surface (the Earth’s surface) to a flat surface.
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an imaginary light is “projected” onto a “developable surface” a variety of different projection models exist
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secant cone
tangent cone
cone as developable surface
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tangent cylinders
cylinder as developable surface
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plane as developable surface
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Map projections always introduce error and distortion
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Map projections always introduce error and distortion
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y)(x,y)(x, ff
input outputunprojected projectedangles (lat/long) Cartesian coordinates
Exactly what are map projections?
Sets of mathematical equations that convert coordinates from one system to another
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How do projections work on a programmatic level?
o each set of "coordinates" is transformed using a specific projection equation from one system to another
o angular measurements can be converted to Cartesian coordinates
o one set of Cartesian coordinates can be converted to a different measurement framework
Projection, zone, datum (units) X Y
geographic, NAD27 (decimal degrees)
-122.35° 47.62°
UTM, Zone 10, NAD27 (meters) 548843.5049 5274052.0957
State Plane, WA-N, NAD83 (feet) 1266092.5471
229783.3093
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How does ArcGIS handle map projections in data frames?
o Project data frames to see or measure features under different projection parameters
o Applying a projection on a data frame projects data “on the fly.”
o ArcGIS’s data frame projection equations can handle any input projection.
o However, sometimes on-the-fly projected data do not properly overlap.
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How does ArcGIS handle map projections for data?
Projecting data creates a new data set on the file system
Data can be projected so that incompatibly projected data sets can be made to match.
ArcGIS’s projection engine can go in and out of a large number of different projections, coordinate systems, and datums.
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Cassini projection of the world
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Coordinate Systems
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Cartesian CoordinatesCartesian Coordinates
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Coordinates
Features on spherical surfaces are not easy to measure
Features on planes are easy to measure and calculate
distance angle area
Coordinate systems provide a measurement framework
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Coordinates
Lat/long system measures angles on spherical surfaces
60º east of PM55º north of equator
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Lat/long values are NOT Cartesian (X, Y) coordinates
constant angular deviations do not have constant distance deviations
1° of longitude at the equator 1° of longitude near the poles
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Coordinate systems
Example of coordinate/projection systems
Universal Transverse Mercator (UTM)
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Coordinate systems
Universal Transverse Mercator (UTM)
Based on the Transverse Mercator projection
60 zones (each 6° wide)
false eastings
Y-0 set at south pole or equator
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Coordinate systems
Every place on earth falls in a particular zone
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Datums
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Datums
A system that allows us to place a coordinate system on the earth’s surface
Initial point
Secondary point
Model of the earth
Known geoidal separation at the initial point
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Datums
Examples of used datums
NAD83 North American Datum World Geodetic System of 1984 (WGS84)
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geodetic datumالمسند الجيوديسي
المساحةهو المرجUع الUذي اشUتقت منUه أنUواع القياسUات. ففي علمي هUUUUوU المس!!!ن!د! الجيوديس!!!ي!، فإن(األرض قياسات) والجيوديسيا
مجموعUة مUن اUلنقUاط اUلمرجعيUة عUلى سUطح األرض توضUعU في مقابلهUا ا UنمUوذج متصUل UلشUكل األرض ( �Uأيًض (UالبUالغU) ع، وفيUموضUات الUقياس
نظام اإلحداثيات الجغرافية)U لتحديUدU مجسم القطع الناقص المرجعيسUنUاUد األفUقيUةU لUوصUف نUقطUة علىU سUطح Uاإل UعUجUاUخدم مرUتUتسUاألرض. و ،
U ا �Uللعرض الجغرافيوفقU ر. والطول الجغرافيUاثي آخUدUام إحUنظU Uو أيUأ رتفاعUات أو األعمUاق. Uودي تقيس االUد العمUناUاإلس UعUمراجU في حين أن
U ن ووالرسم التخطيطي الهندسة التطبيقيةوفيUوUUUUUUمرج!!!!!ع ، يك هUو نقUطUة مرجUعيUة أUو سUطح أو محUور، لهUدف يتم إجUراء اإلس!ناد!
القUيUاسات UفUي مقUابUله.
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نقاط اإلسناد المرجعيه
طحUUة على سUUة وثابتUUاط معروفUUة هي نقUUناد المرجعيUUاط اإلسUUنقرض تسUUتخUدم لوUصUUف مUوقUUع UنقUUاط غUUيرU معروفUUة على األرUض. UاألU ارUف أقطUاUا أنصUون لهUكUد يUق UةUرجعيUالم UنادUاط اإلسUا ألن نق ونUظUر�
ونقUاطU مركUزيUة مخUتلفUة، UفUإن نقطUة معينUة علىU سUطح UاألرUض يكUون ا لنUقطUةU اإلسUناد اUلUمسUتخدمةU في �Uك وفقUلUة وذUتلفUت مخUاUاثيUدUحUا إUلهسUنادU اUلUمرUجعيUة UإلUاU اطUقUمن نU تUاUلمئUد اUتوجU ذاUلهUياس. وUالق UءUاUرUإجU UةUUرجعيUمU UةUUلنقط Uا �UUقUا وفUدهUUديUتح UتمUي يUتUUلUوا U،ل األرضUوUUح UةUUليUالمح
ئمUة. وUتهUدUف نقUاطU UاإلسUنUادU الUمUعاصUرة،U UوالUتي تعUتUمUد بشUكل Uمال UةUيUمحلرUض، إUلىU تغطUيUة منUاUطUق UألUل اUكUلشU ةUدقيقUال UاتUسUاUيUالق UلىUع UدUيUاUزUمتأكUبرU. وUتUعUد أكUثUرU نقUاUط UاإلسUنادU اUلUمUرجعيUةU شUيوUع�Uا Uفي UاالسUتخدام في
.WGS84و،NAD83و، NAD27 هيU أمريكا الشمالية
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Matching Matching DatumsDatums
Revenge of Revenge of the the ShiftShift
I use GPS for all my mapping. I’m using NAD83(1986)
I’m using WGS84
4.3 ft
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WGS 84WGS 84 إنه اإلطار المرجعي الذي 1984هو النظام الجيوديسي العالمي لعام .
والذي حددته الوكالة الوطنية لالستخبارات ) DoDتستخدمه وزارة الدفاع األمريكية (وكالة رسم الخرائط الدفاعية سابق�ا، ثم الوكالة الوطنية ) (NGAاألرضية الفًضائية (
في جميع WGS 84للصور ورسم الخرائط). وتستخدم وزارة الدفاع األمريكية نظام أغراض رسم الخرائط، والمخططات، والمساحة، والمالحة، بما في ذلك مدارات
البثي" و"الدقيق". "GPSالنظام العالمي لتحديد المواقع
وال يستخدم اليوم أي نظام مرجعي عالمي سوى نظام اإلسنادWGS84 ، والمطابق�ا لنظام اإلسناد هو نظام WGS84في أمريكا الشمالية. كما أن نظام NAD83تقريب
الترفيهية GPSاإلسناد القياسي االفتراضي لإلحداثيات المخزنة في وحدات والتجارية
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Projecting spatial data sets
UTM 36
UTM 34
Lake Victoria is not in central Africa
Used for going between projectionsSource data sources may not be compatible
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Projecting spatial data sets
Used for going between projections• Data sets are now compatible
Lake Victoria really is in east Africa
both arenow UTM 34