Pathfinding and region performance – Lorca Linden comments

Nalates Urriah has been keeping an eye on the more technical aspects of pathfinding, and has routinely provided excellent updates and commentary on the project. Her work is largely the reason I’ve not delved overly deeply into the subject here, and why my own Pathfinding overview attempts to cover the subject from a lay user’s perspective.

Alongside yesterday’s roll-out came a lot of confusion regarding pathfinding and its impact on region performance. As a result of this, Nalates published a piece seeking to clarify matters. If you are concerned as to the impact of pathfinding, and you’ve not already done so, I thoroughly recommend you give her article a careful read.

Today, Lorca Linden took the extraordinary step of commenting on Nalates blog in order to lend further clarification on the subject. While I do not agree with his stated reasons as to why Linden Lab did not communicate more on the actually roll-out (which, in fairness, has potentially contributed to the confusion / misinformation circulating about pathfinding), the key points of Lorca’s comments vis-a-vis overall performance are nevertheless important in helping to spread better understanding of the matter. I’m therefore reprinting his comments here in full, with the key paragraph on performance underscored, in the hope that it will help them reach a wider audience.

“Although Lindens do not generally post on Resident blogs, I am going to make an “exception in this one case. Don’t expect us to make a habit of it, though 🙂

“I want to start off by thanking Nalates for what I feel has been even-handed coverage of pathfinding as a whole. While I disagreed with several of the assertions made in the “Tsunami” post, it did make us realize that there were misconceptions about pathfinding that needed clarification (particularly in regards to performance implications) and was a useful data point in identifying Resident concerns while we were still in the development phase.

The 18% performance hit figure referenced on the Phoenix Viewer blog is a worst case scenario that will rarely be seen in practice – eg, you could see that large of a hit on a poorly optimized region that contains hundreds of pathfinding characters running simultaneously. Average perceived (viewer side) fps grid wide was actually .03 fps higher yesterday afternoon than it was the afternoon before. Average server-side performance grid wide was also inline before and after pathfinding server code was rolled out. Region crash rates – excluding a bumpy couple hours during the roll out – remain low. All of this is to say that as far as the Lab can tell, Pathfinding has not had a negative performance or stability impact in the vast majority of situations.

“I also want to make clear that the impact on some vehicles is not directly related to pathfinding per say but rather the underlying physics and terrain optimizations that made pathfinding possible and have benefits beyond pathfinding. As far as we can tell, only a small percentage of existing content is affected by this physics upgrade.

“We do not consider pathfinding to be fully released until the pathfinding viewer tools are out of beta. This is why we have not yet made an official announcement. I agree that we need to do a pass on our pathfinding related wiki as some of the information there has not been updated since we were in alpha. We plan to make a blog post in the near future that will address some common misconceptions we have heard about pathfinding. We also plan to continue updating the “Good Building Practices” guide so that it will be a useful resource for Residents looking to make optimized content.

“We understand that pathfinding can be a confusing topic at times and appreciate the effort interested Residents are making to absorb the technical details. If you have any burning questions about pathfinding, please come to our user group on Pathtest1 (on Aditi) at 4PM SLT Thursdays and ask away. Above all, we are extremely excited to see what you Residents create with the new pathfinding tools and LSL functions!”

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Curiosity: Sol 3: first colour panoramic image

Jut after I pressed my most recent update on the Mars Science Laboratory mission, NASA JPL release the first low-resolution colour panoramic view of Gale Crater captures by Curiosity’s Mastcam.

The images were captured by the Mastcam system’s 34 mm fixed focal length camera mounted towards the top of the rover’s remote sensing mast (it is the Mastcam camera on the left of this image).

First colour panoramic view of Gale Crater from Curiosity’s Mastcam

The mosaic is made up of 130 images each compressed into a 144×144 pixel format for transmission to Earth. The complete set of images has been brightened in the processing as Mars only receives half the sunlight Earth does, and these images were captured in the late Martian afternoon. The black areas denote areas outside the view of the Mastcam. The grey patches on the ground to the left and right of the rover are the result of the blast from the descent stage’s radial motors striking the ground and blowing away the topsoil, and these are already the subject of study by the science team on the mission.

A closer view of one of the blast areas resulting from the MSL’s descent stage motor thrust

The dunes on the horizon are also visible in the black-and-white panoramic view captured by Curiosity’s Navcam on Sol 2, but in this image they reveal some interesting hues that suggest they are comprised of different materials or textures.

Selected high-resolution (1200×1200 pixel) images from the panorama are expected to be returned to Earth later.

Image credit: NASA / Caltech / Malin Space Science Systems (MSSS)

MSL coverage in this blog

Curiosity: Sol 0 to Sol 2

It’s been an amazing few days since Curiosity landed on Mars. The rover is off to a good start in what is called the “characterisation activity phase” of the mission, which is scheduled to last around a month.

The rover landed on Mars at 15:00 “Mars time”, equating to 06:14 BST on August 6th, or  22:14 PDT August 5th, at NASA’s Jet Propulsion Laboratory in Pasadena, with confirmation being received on Earth at 06:32 / 22:32 respectively .

This marked the start of the rover’s first day on Mars, officially designated Sol 0. Activities during Sol 0 comprised releasing various instruments and protective covers, such as those over the Hazcams at the front and rear of the rover, checking-out the UHF telecommunications system and the rover motor controller, confirming its orientation (facing a heading of 112.7 degrees (+/- 5 degrees) and with a slight tilt) and relaying some 5 Mb of data back to Earth via Mars Odyssey.

Sol 1

Sol 1 saw the rover gather data from the Radiation Assessment Detector and Rover Environmental Monitoring Station instruments and further tests on the high-gain antenna (HGA), located towards the back of the vehicle. This is important, as the HGA enables the rover to communicate directly with Earth when it is above the rover’s horizon, rather than signals having to be relaid via Mars Odyssey and Mars Reconnaissance Orbiter (MRO) – although both of these will continue to be used when direct rover-Earth lines of communications are unavailable.

Curiosity took its first colour image of Mars using the Mars Hand Lens Imager, or MAHLI, located on the robot arm. This image appeared oddly rotated due to the arm being in its stowed position, MAHLI pointing outwards on the front left side of the rover.

First MAHLI image, taken with the camera in its stowed position, looking over the side of the rover. In the distance is the rim of the crater

The image appears cloudy as it was taken before MAHLI’s protective cover was still in place, coated by a film of dust thrown-up by the descent stage motors during landing.  The image is facing north, and the visible ridge is the rim of Gale Crater, with the peak to the left being some 1,150m (3,775 ft) high and 24 km (15 miles) from the rover

Sol 1 also saw the rover complete an initial deployment of the forward remote sensing mast to enable calibration of the navigation cameras (Navcams) to commence. Calibration was expected to take around a Sol to complete, as test images of targets on the rear section of the vehicle had to be returned to Earth in order for any “manual” adjustments yo the camera systems to be calculated and then transmitted back to the rover.

MAHLI’s image (above) given context is a computer simulation of Gale Crater developed from hi-resolution images returned by MRO’s HiRISE and the High Resolution Stereo Camera on Europe’s Mars Express.

During Sol 1, MRO also captured a fabulous image of the landing zone from some 300 km above the surface of Mars, using it’s HiRISE camera system. The image clearly shows the shadow cast by Curiosity, together with parachute and aeroshell to the left and slightly below it (approx. 615m away) and the impact points for the heat shield (some 1.5 km (1 mile) from the rover) and descent stage. The latter, having flown clear of the rover’s landing-zone, impacted on the surface around 650 metres from the rover, leaving a classic oblique impact mark (common to asteroids striking a planet), which forms an arrow pointing back towards the rover. This image was later combined with images of Mars to create a short movie called Zooming in on the scene of Curiosity’s Landing.

Sol 2

Curiosity’s remote sensing mast, seen fully deployed prior to launch in 2011

On Sol 2, Curiosity completed calibration testing on the Navcams, and raised the remote sensing mast to its fully deployed position. An initial high-resolution image was then captured by the Navcam, looking out over the front of the rover (part of an exercise to help confirm the rover’s alignment relative to the sun).

The first image taken by the Navcams following full deployment of the remote sensing mast. The cameras are looking forward and down over the front of the rover, away from the sun (what JPL calls the “anti-sun” image)

Following this, the mast was rotated, allowing the Navcams to be used to capture images of the rover’s immediate surroundings, including a 360-degree panoramic collage of Gale Crater and Aeolis Mons (referred to as “Mount Sharp” by NASA, the unofficial name given to the mound prior to its naming by the IAU). The panoramic view was initially returned to Earth as a collage of thumbnail images.

The first 360-degree panoramic view of the landing site and Gale Crater returned as thumbnails by Curiosity

As it is currently only available at thumbnail resolution, the panoramic view was somewhat overshadowed by high-resolution images also returned by the Navcams, which stand as promise of things to come once the Mastcams start operations.

The Navcams were also used to image elements of the rover itself in order to gain a further indication of the vehicle’s overall condition, and these revealed no nasty surprises, and were later strung together to give and overhead “fish-eye” view of  Curiosity (see the image towards the end of this article).

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