lab 1: projection yingjie hu. what is a projection? a projection is the rendering of the earth’s...
TRANSCRIPT
Lab 1: Projection
Yingjie Hu
What is a projection?
• A projection is the rendering of the earth’s round, three-dimensional surface onto a flat map.
Projection
What do we need to make a projection?
• A surface• A method to project the features of the earth
on our surface
Surface
• Plane surface• Azimuthal projection (planar projection)
Surface
• Cylinder • Cylindrical
Surface
• Cone• Conic
How to project? Surface aspect
• Equatorial
Surface aspect
• Transverse
Surface aspect
• Oblique
Surface aspect
• Polar
Tangency
• Definition– Location at which the projection surface and the
globe touch.
Secancy
• Definition– Location at which the projection surface cuts
through the globe
Distortion
• The earth has a curved surface. When transforming the round globe to a flat surface, we will inevitably lose accuracy at places where the “paper” doesn’t touch the globe.
Map properties
• Conformality (Conformal projection)– Retention of correct angles on a map– Retaining the shapes and directions of the
features on the earth– Lose the accuracy of area– Applied in navigation
Map properties
• Equivalence (Equivalent projection)– Retention the accuracy of the area on a map– Lose shape and direction of the features on the
globe– Applied in area calculation
Map properties
• Compromise projections– Neither conformal nor equivalent– Avoid extreme distortion of one map property
Map properties
• Short summary– Distortion is inevitable, since the globe is round
while paper is flat.– Preserving one property (shape) results in the
distortion of another property (area).– Conformality retains shape and direction, but it
loses area accuracy. Equivalency has the opposite properties.
How can we get the projection information from a map?
• Surface type– From the shapes constituted by longitudes and
latitudes
Cone
How can we get the projection information from a map?
• Surface type– From the shapes constituted by longitudes and
latitudes
Cylinder
How can we get the projection information from a map?
• Surface type– From the shapes constituted by longitudes and
latitudes
Plane
How can we get the projection information from a map?
• Surface aspect– From the area focused by the map
Polar
How can we get the projection information from a map?
• Surface aspect– From the area that has the least distortion.
Equatorial
How can we get the projection information from a map?
• Surface aspect– From the area that has the least distortion.
Transverse
How can we get the projection information from a map?
• Surface aspect– From the area that has the least distortion.
Oblique
How can we get the projection information from a map?
• Conformality – The shape is preserved.– The area of the features is distorted.
How can we get the projection information from a map?
• Equivalence– The area is preserved.– The shape of the continents is distorted.
Assignment
• All the materials are on Gauchospace.• Answer all the questions, print your answer
sheet, and submit it in the next lab class.• Due date: Oct. 6th (Next Thursday).• Homework which is turned in late will lose
10% of the full score each weekday. Homework which is submitted after 5 weekdays will not be accepted.