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Lidar & Overlapping UTM Zones

Second zone DEM imported

by Rob Plowright

Intro by Ken: Other than Tasmania & ACT, all states & territories have 2 zones. NZ has just one zone. I recall struggling with marrying datasets from 2 zones for a map that was close to the edge of 54/55. So Rob’s experience will be valuable for the few who are faced with this issue. The general process will also apply to other types of data.

Coping with Australia’s 4 zones

Now that didn’t work

The other day I was doing some virtual exploring: processing lidar in OCAD to see if I could find some interesting terrain. One area I was interested in just happened to be on the boundary between UTM zones 55 and 56; first time I had experienced this. Getting adjacent lidar tiles from different zones to line up in one OCAD file proved to be more difficult than expected. After trying several different approaches and getting nowhere I finally managed to do it, with the help of a suggestion from Ken.

This involved processing the tiles in one zone then using Map > Transform > Change Coordinate System to change the map into the next zone, then processing the remaining tiles. There was one problem however: while the map (contours) transformation went well, the background images (hillshade, vegetation, etc)  did not.

Ken asked me to write-up the process for his up for his blog. Since there was the problem with the background images not transforming properly I sent the first draft to OCAD support. Gian-Reto got right back to me saying that while the method I described would work, there was a quicker way – just using the DEM Wizard. “That’s odd” I thought, “I tried that and it didn’t work”. Gian-Reto soon figured out there was a bug that meant southern hemisphere UTM zones did not process properly and he promptly fixed it.

So just in case anyone wants to know, here is how to do it.

The works

The lidar coverage

I will use an example from Kanangra in the Blue Mountains (not the area I was looking at – which shall remain secret for now).

  • I have five lidar tiles: two in zone 55 and three to the east of that in 56. They are:
    • Taralga201611-LID2-C3-AHD_7746232_55_0002_0002
    • Taralga201611-LID2-C3-AHD_7766232_55_0002_0002
    • Burragorang201805-LID2-C3-AHD_2226232_56_0002_0002
    • Burragorang201805-LID2-C3-AHD_2246232_56_0002_0002
    • Burragorang201805-LID2-C3-AHD_226232_56_0002_0002

As you can see from the double digit components above, the Taralga tiles are in zone 55 and the others in 56

Each tile is 2km x 2km and the numbers after ‘AHD’ give you the grid reference for the SW corner of the tile. So the  SW corner of the first Taralga tile is at 774000 6232000. and the first Burragorang tile is at 222000 6232000  You will notice that the Burragorang tiles have the same northings (6232000) as the Taralga tiles but different eastings.

1. Select co-ordinate system

The area is mostly in Zone 56 so I have decided to make the OCAD file zone 56. Set up a map in zone 56.  First process the zone 55 (Taralga)  tiles. (You could just as easily do zone 56 first).

Select co-ordinate system
Selecting co-ordinate system

The map now looks like this.

Lidar image
Lidar image first zone

Contours (5 and 25m)  are in grey and vegetation height is in the background (I have not bothered rotating the map to magnetic north for this exercise). The blue border shows the OCAD DEM boundary (which is oriented to zone 56)  but I have drawn in the actual boundary of the Taralga tiles’ data with the purple dashes. As you can see the Taralga tiles are sightly rotated relative to the Burragorang tiles, as you would expect since they are oriented to zone 55.

Looking closely
Rotation artifacts

If you look closely there is a little bit of junk in the gaps between the OCAD DEM and the actual (rotated) Taralga tiles.

2. Processing the other zone dataset

Now process the Burragorang tiles – but this time, in the DEM Wizard, make sure it says zone 56 for the DEM tiles.

DEM import next zone
Setting co-ordinate systems for next zone

Now the map looks like this…

Second zone DEM imported
Second zone DEM imported

I have made the Burragorang contours red for the sake of this exercise.

If you look closely at the above image, you can see that there is a large overlap between the westernmost Burragorang tile and the easternmost Taralga tile; almost a whole 2 x 2km tile. It is not always this much. In the area I was looking at before, it was only about 500-600m.

Also in the close-up below, you can see that the red and grey contours  are not exactly the same. This is because the two lidar sets are from different flights: Taralga 2016 and Burragorang 2018. In the other area I was looking at, both lidar sets (zone 55 and 56) were from the same year, and obviously from the same flight, as they matched exactly.

Difference in contours
Close up of difference in contours

The red contours above are more detailed (noisier) as, being more recent, that lidar is higher resolution. If  this map is just for a base map the slightly different contours is not necessarily a problem. But if you want to eliminate the overlapping contours you can crop one set.

3. Eliminate overlap

Since the Burragorang contours are more recent I am going to crop the Taralga contours. Start by hiding the Burragorang (red) contours and draw an area (light blue in this example)  over the parts you want to crop. Then use the Object > crop objects tool. You can also draw the cropping area so as to remove the junk around the edges.

Cropping the overlap
Cropping the overlap

And I get this…

Cropped overlap
Cropped overlap

Unhide the red contours to get this…

The full picture
The full picture

Up close the border between the zones looks like this…

Close up of the join
Close up of the join

Tips

  1. This process, excluding the DEM aspects, can also be used for non-lidar datasets over 2 zones.
  2. If you are new to lidar processing then download one of my DEM templates for use with the DEM Import Wizard. The template has 15 differentially coloured symbols to cover each of the contour selections in the wizard and to avoid confusion with any brown contours in your main or background map. Get one at ocad.com.au/mapping-resources
  3. If you have distortion in a small area, check out Map > Transform > Local transformation. It makes the adjustment of existing maps to geo-referenced base maps (hillshading, orthophotos etc.) easier and more accurate.
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New OCAD Lidar Features Example

Cornish Hill lidar vegetation height image

ELVIS lidar data processed through OCAD 2018 DEM import

Mark Roberts recently reported

Just a note that I recently downloaded some lidar data from ELVIS and imported to OCAD 2018 and the results are spectacularly good. The vegetation height function depicts clearings and buildings perfectly:

OCAD 2018 import from ELVIS Lidar image
Mark’s OCAD 2018 import from ELVIS Lidar

Mark later remarked that lidar is becoming very readily available and the OCAD processing of lidar is so easy.

VIC lidar data processed through OCAD 2018 DEM import

Following Mark’s report I received ordered lidar data for a permanent orienteering course in Daylesford, VIC. Here in VIC we do not yet have free access, however on behalf of Orienteering Victoria I have established a protocol with DELWP for access to lidar data. As their paid orders take priority it takes some weeks to fulfill an order but the wait is certainly worthwhile.

I processed the ‘irregular points’ las files through OCAD 2018 DEM import wizard, selecting all options. This provided seven background images such as hill shading, slope gradient and hypsometric shading.

Continue reading New OCAD Lidar Features Example

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OCAD Inc’s Advent Calendar

OCAD Inc logo

OCAD’s Advent Calendar of functionsTopo socks

If you are on Facebook or Twitter then it may be well worth your while following OCAD Inc for a stream of useful functions. December 1st is about the DEM Import Wizard.

December  2nd is on moving building edges easily. Bet many of you didn’t know that one.

December 3rd is for course planners being on automatic control descriptions.

These are great introductions to OCAD for tyro OCAD users and reminders for we more mature OCAD users.


Aiming off…

Santa and sack
Santa Jymbo delivers

Free delivery for our Pretex buyers to Canberra. If you will be there then save big on delivery costs.

Jim Russell will be in Canberra on 15th December 2017 and Australia Day 2018. Place your order online and request Jim’s delivery on the order notes.

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Become More Productive with OCAD in 2017 – Part 2

New Year resolutions that will stick

Here are some matters that puzzled me or other mappers, but were eventually resolved. Take a browse to up your OCAD productivity.

Multiple OCAD instances

After an OCAD update to a new version (such as 11 to 12), do not be tempted to run both versions simultaneously on the one PC. The same temporary file names are used by both versions.

Characters inserting/deleting 1 or more places away from cursor?

I use cartographic fonts and a few fonts with slightly quirky styles. For many months while editing blocks of text on maps, I blamed my laptop for letters being inserted and deleted 1 or more places from the insertion point. After moving to a desktop PC and having the same issue, I thought to ask Mark Roberts who replied ‘ligatures’.

Ligatures are 2 or more letters combined into one character. ff, ae, fi, ffi, ft are often combined in a font that enables ligatures. See Wikipedia for more. OCAD recognise ligatures as a single character whereas your OS and you are seeing it as multiple. So if I write difficult in OCAD using a ligature font, OCAD thinks the cursor is 2 characters prior (the ffi being a single character). Note that ligatures in a block of text are cumulative in effect.

A 25 second video showing a normal insertion and then a ligature effected insertion. Deletions are similarly affected.

Solution 1 – do not use fonts with ligatures.

Solution 2 – once you understand there is a pattern, it is fairly easy to edit small blocks of text with ligatures.

A DEM elevation profile is back to front?

OCAD DEM elevation profile image
OCAD DEM elevation profile

You may have merged many segments of track, or drawn a long curvy track, only to find the profile depicts the opposite direction of travel.

This is because the elevation profile function uses the direction in which the line was drawn (or traveled in the case of GPX tracks). Simply Object>Reverse Object Direction and redo the elevation profile. It is also a symbol on the menu that you might know better as the symbol to reverse the direction of fence tags.

 


Aiming off

On a stressful day, this is a calming 5 minute video. Though I’m not sure which is the more calming – the scenery or the voice.

Of all the paths you take in life, make sure a few of them are dirt. [John Muir]

 

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New Hypsometric Ramps for OCAD DEM Based Maps

Hypsometric tinting ramps expand

OCAD DEM colour ramps image
OCAD DEM colour ramps

The mapper of smaller scale maps such as trail maps, may be interested to know that three new colour ramps have been added to the hypsometric tinting choices in a coming OCAD update. One ramp allows choice of colours in up to 10 bands.
 

 

Brown – Yellow colour ramp

Brown - Yellow hypsometric image
Brown – Yellow hypsometric

Brown (high elevation) – Yellow (low) offers a ramp similar to that of the Sustrans UK touring cycle maps. It is easy on the eye yet effective. The ramp in the image is at 50m intervals on a 1:100,000 scale map (and like our Spa Country Explorer trail maps, it is printed on Pretex).

Research shows that many users of hypsometric tinted maps think that colours have meaning for ground content as well as elevation. For example a tint that has green at the lowest level implies to those users that the green also represents forest or farmland. Therefore there has been effort to avoid colour ramps that could give rise to such confusion.

On the full map of the Brown – Yellow image, the cartographers have added a green overlay for specific forest sections. Those are not large areas so it does work well. (See Shaded Relief website below for an article Evaluating Cross Blended Hypsometric Tints)

Red – Yellow colour ramp

Lerderderg Red-Yellow ramp image
Red-Yellow hypsometric

While Brown – Yellow colour ramp tends towards subtle, Red – Yellow is striking yet not glaring. The ramp used in the image is per 100m on part of an 80km trail trial map. The yellow is the Lerderderg Gorge (VIC).

I also trialled showing 50m contours on this 100m ramp. It may well be useful for less expert mountain bike riders who may be more conscious of elevation change when planning trips.

Colour yourself purple

The Greyscale Interval colour ramp is very useful addition. It produces a greyscale 10 segment ramp with each segment at your specified contour interval.

Using an image processing tool you can select each greyscale level in the resulting TIFF background  file and change to a colour of your choosing.

After processing a segmented greyscale, I started up the ubiquitous IrfanView (free but well worth a donation). Sure enough, I found it had the ability to easily select a greyscale and change it to another colour. Below is the before and after image I generated using this process. Not a colour ramp you would use for real but you are welcome to add it to your art collection 🙂

Selectable hypsometric tints OCAD & post-OCAD image
Selectable hypsometric tints OCAD & post-OCAD

Further reading

For those interested in exploring hypsometric tinting specifically or shaded relief generally, then these two websites are good resources.

Shaded Relief website

Relief shading website Some superb hand drawn relief shading including an example produced during 1838-45. I learnt that DEM based relief shading is termed Analytical Relief Shading.

Jim’s Cartography website has some viewable maps that use relief shading effectively without including contours. Jim Lewis is a NZ  OCAD user.