SOME EXPERI ENCES I N ANALYTI CAL RELI EF SHADI NG Draen Tuti - - PowerPoint PPT Presentation

▶
some experi ences i n analyti cal reli ef shadi ng
SMART_READER_LITE
LIVE PREVIEW

SOME EXPERI ENCES I N ANALYTI CAL RELI EF SHADI NG Draen Tuti - - PowerPoint PPT Presentation

Nov 05, 2022 561 likes •873 views

SOME EXPERI ENCES I N ANALYTI CAL RELI EF SHADI NG Draen Tuti Miljenko Lapaine Vesna Poslon ec-Petri dtutic@geof.hr mlapaine@geof.hr vesna.posloncec@zg.t-com.hr Faculty of Geodesy, University of Zagreb CROATI A INTRODUCTION

slide-1
SLIDE 1

SOME EXPERI ENCES I N ANALYTI CAL RELI EF SHADI NG

Dražen Tutić

dtutic@geof.hr

Miljenko Lapaine

mlapaine@geof.hr

Vesna Poslončec-Petrić

vesna.posloncec@zg.t-com.hr

Faculty of Geodesy, University of Zagreb CROATI A

slide-2
SLIDE 2

INTRODUCTION

  • Croatia has a number of mountains
  • Shaded reliefs in Croatia were done manually

until recent days

  • Today, cartography in Croatia is in expansion

– new series of the official topographic maps – national strategy towards tourism has encouraged publishers to provide all kinds of map products

  • Increasing need for relief shades
slide-3
SLIDE 3

CROATIAN RELIEF (SRTM data)

  • Geomorphology of

Croatian mountains:

– 95 % sediment – 2-4 % metamorphic – 1 % vulcanic

  • Karst (krš) with

it’s irregular shape is difficult to present with shades

slide-4
SLIDE 4

MEDVEDNICA MOUNTAIN

  • Peek – 1035 m – 10 km from Zagreb’s main

square

  • The most visited mountain in Croatia
  • The largest number of cartographic

representations among Croatian mountains

  • DEM of Medvednica derived from contours from

the topographic map at the scale of 1:25 000 will be used for examples

slide-5
SLIDE 5

Perspective view of DEM

The main ridgeline is in SW-NE direction with spurs perpendicular to this direction

slide-6
SLIDE 6

Top of Medvednica (Lovrić, 1993)

N

Average direction of light

Shades are drawn manually. Adaptive direction

  • f light
slide-7
SLIDE 7

Panoramic view

N

Direction of light

Artistic hand drawing

slide-8
SLIDE 8

Bicycle map of Medvednica

N

Direction of light

Analytical shading of digital relief model.

slide-9
SLIDE 9

Photograph of the relief model (source unknown)

N

Direction of light

slide-10
SLIDE 10

Hand drawn shades, by Ante Čala

N

Direction of light

slide-11
SLIDE 11

MOTIVATION

  • Absence of people specialized for manual relief

shading

  • Shades prepared for one map usually cannot be

reused for other maps

  • Investigate analytical relief shading and modify it

to better serve the purpose for topographic and thematic maps

slide-12
SLIDE 12

METHODOLOGY

  • Brassel’s work “Ein Modell zur automatischen

Schräglichtschattierung”, 1974.

  • Modification of the azimuth, height and length of

the vector of light

  • The goal: Weight of shades on the map: as small

as possible while preserving the best perception

  • f the relief
slide-13
SLIDE 13

Weight of shades

  • raster matrix of shaded relief with values [0,255]

calculated weight by this equation have relative meaning and does not represent final weight on printed map.

slide-14
SLIDE 14

Weight calculated by equation

100% 0% 50%

slide-15
SLIDE 15

DIFFUSE SHADING

ij

r v

, ,

  • normal vector of relief surface
  • vector of light

Cosine of the angle between vectors and . Linear transformation from [min(Dij),max(Dij)] to [0,255]

slide-16
SLIDE 16

Vector of light

, ,

triple xij, yij, zij defining the radius vector height above horizon azimuth length

slide-17
SLIDE 17

Diffuse shading A=135° H=45° I=1

N

Direction of light

Weight: 27%

slide-18
SLIDE 18

Modification of azimuth

Calculate the aspect with starting direction (135°)

( )

( )

ij ij

a a sin arcsin =

. const ij

A A =

ij const ij

a A A ± =

. ij

a

Transformation to the first quadrant: Final azimuth of the light:

slide-19
SLIDE 19

First step: aspect map with 135° as starting direction 0° 180° 360°

0° 90° 180° 270°

ij

a

slide-20
SLIDE 20

Azimuth of the light 45° 135°

45° 135° 0°

ij const ij

a A A ± =

.

slide-21
SLIDE 21

Modificaton

  • f azimuth

N

Direction of light

ij const ij

a A A ± =

.

Weight: 28%

slide-22
SLIDE 22

Comparison

slide-23
SLIDE 23

Modification of height

Calculate the slope of relief

ij

S

ij ij

S H − ° = 90

Let the height be perpendicular to the slope:

slide-24
SLIDE 24

0° 90° 0° 90°

Slope Height

slide-25
SLIDE 25

Modification of azimuth and height

N

Direction of light Height of light

Weight: 14%

slide-26
SLIDE 26

Modification of the length of vector

( ) ( )

1 min =

mn

R I

( ) ( )

k R I

mn

= max

( ) ( ) ( )

( ) 1

min min max 1 + − − − =

mn ij mn mn ij

R R R R k I

( ) ( )

( )

mn ij mn flat ij

D D D D R min min 255 − − = 255 >

ij

R

,

255 =

ij

R

  • length of the light vector for minimum elevation
  • length of the light vector for maximun elevation

Linear relationship between the length and elevation Transformation to the grayscale

If then

slide-27
SLIDE 27

All three modifications

Direction of light

N

Height of light

Weight: 9%

Length of vector

slide-28
SLIDE 28

CONCLUSION

  • Light vector as function of relief model can give

different results

  • Presented modifications are simple and easy to

interpret, and applicable to any relief model

  • Modificated results can be used for easier

creation of final shades

slide-29
SLIDE 29

Overlay of the shades on the map

Standard diffuse shading Modification of the azimuth and height

  • f the light (our approach)
slide-30
SLIDE 30

Thank you!